[PATCH v3 0/3] erofs-utils: introduce fuse implementation

[PATCH v3 0/3] erofs-utils: introduce fuse implementation

[Gao Xiang via Linux-erofs]

From: Gao Xiang <hsiangkao@redhat.com>

changes since v2:
 - erofs_dbg() -> erofs_dump() in signal_handle_sigsegv() (Guifu);
 - get rid of unnecessary new lines (Guifu).

changes since v1:
 - fix off-by-one error of namebuf in erofs_fill_dentries();
 - drop unused "struct erofs_super_block super;" in lib/super.c; 
 - fix clang/32-bit build errors founded by travis CI.

Hi all,

I've finished cleaning up erofsfuse - a fuse implementation of erofs
just now. It's now considered as multithread safe since it's
currently stateless by killing useless caches and using high-level
libfuse APIs(also libfuse itself is MT-safe). Therefore, I don't
need to release another liberofs MT-safe version for now as well.

As I said eariler, the main usage of erofsfuse is to support handling
erofs images on older kernels without kernel modification, which
was requested by real vendors (thanks to folks from OPPO to pick
it up).

And to summarize the benefits of erofsfuse, I think it would be:

 - erofs images can be supported on various platforms;
 - an independent unpack tool can be developed based on this;
 - new on-disk feature can be iterated, verified effectively.

erofsfuse will be included in the upcoming erofs-utils v1.2, but
disabled by default for now. Since it still needs sometime to
stablize and also notice LZ4_decompress_safe_partial() was broken
in lz4-1.9.2, which just fixed in lz4-1.9.3 days ago [1].

BTW, recently some other people get in touch with me in private
to ask for some latest micro-benchmark among compression fses,
so I spared some extra time on this as well, see:
https://github.com/erofs/erofs-openbenchmark/wiki/linux_5.10_rc4-compression-FSes-benchmark
I might test on hikey960 board as well yet need to seek more
extra time but I think no much difference on relative
relationship (but yeah, CPU-storage combination is vital for
seqread uplimit).

Thanks,
Gao Xiang

Cc: Li Guifu <blucerlee@gmail.com>
Cc: Huang Jianan <huangjianan@oppo.com>
Cc: Guo Weichao <guoweichao@oppo.com>

Huang Jianan (2):
  erofs-utils: fuse: support symlink & special inode
  erofs-utils: fuse: add compressed file support

Li Guifu (1):
  erofs-utils: introduce fuse implementation

 Makefile.am                |   4 +
 configure.ac               |  22 +-
 fuse/Makefile.am           |  10 +
 fuse/dir.c                 | 103 +++++++++
 fuse/main.c                | 240 +++++++++++++++++++++
 include/erofs/decompress.h |  35 ++++
 include/erofs/defs.h       |   5 +
 include/erofs/internal.h   |  92 +++++++-
 include/erofs/io.h         |   1 +
 include/erofs/trace.h      |  14 ++
 include/erofs_fs.h         |   4 +
 lib/Makefile.am            |   4 +-
 lib/data.c                 | 204 ++++++++++++++++++
 lib/decompress.c           |  87 ++++++++
 lib/io.c                   |  16 ++
 lib/namei.c                | 264 +++++++++++++++++++++++
 lib/super.c                |  78 +++++++
 lib/zmap.c                 | 415 +++++++++++++++++++++++++++++++++++++
 18 files changed, 1594 insertions(+), 4 deletions(-)
 create mode 100644 fuse/Makefile.am
 create mode 100644 fuse/dir.c
 create mode 100644 fuse/main.c
 create mode 100644 include/erofs/decompress.h
 create mode 100644 include/erofs/trace.h
 create mode 100644 lib/data.c
 create mode 100644 lib/decompress.c
 create mode 100644 lib/namei.c
 create mode 100644 lib/super.c
 create mode 100644 lib/zmap.c

-- 
2.24.0

[PATCH v3 1/3] erofs-utils: introduce fuse implementation

[Gao Xiang via Linux-erofs]

From: Li Guifu <blucerlee@gmail.com>

Let's add a simple erofsfuse approach, and benefits are:

 - images can be supported on various platforms;
 - new unpack tool can be developed based on this;
 - new on-disk features can be iterated, verified effectively.

This commit only addresses reading uncompressed regular files.
Other file (e.g. compressed file) support is out of scope here.

Note that erofsfuse is an unstable feature for now (also notice
LZ4_decompress_safe_partial() was broken in lz4-1.9.2, which
just fixed in lz4-1.9.3), let's disable it by default for a while.

Signed-off-by: Li Guifu <blucerlee@gmail.com>
Signed-off-by: Huang Jianan <huangjianan@oppo.com>
Signed-off-by: Guo Weichao <guoweichao@oppo.com>
Signed-off-by: Gao Xiang <hsiangkao@aol.com>
---
 Makefile.am              |   4 +
 configure.ac             |  22 +++-
 fuse/Makefile.am         |  10 ++
 fuse/dir.c               | 103 ++++++++++++++++
 fuse/main.c              | 230 ++++++++++++++++++++++++++++++++++++
 include/erofs/internal.h |  84 ++++++++++++-
 include/erofs/io.h       |   1 +
 include/erofs/trace.h    |  14 +++
 include/erofs_fs.h       |   4 +
 lib/Makefile.am          |   4 +-
 lib/data.c               | 134 +++++++++++++++++++++
 lib/io.c                 |  16 +++
 lib/namei.c              | 246 +++++++++++++++++++++++++++++++++++++++
 lib/super.c              |  78 +++++++++++++
 14 files changed, 946 insertions(+), 4 deletions(-)
 create mode 100644 fuse/Makefile.am
 create mode 100644 fuse/dir.c
 create mode 100644 fuse/main.c
 create mode 100644 include/erofs/trace.h
 create mode 100644 lib/data.c
 create mode 100644 lib/namei.c
 create mode 100644 lib/super.c

diff --git a/Makefile.am b/Makefile.am
index 1d20577068c5..b804aa90efa9 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -4,3 +4,7 @@
 ACLOCAL_AMFLAGS = -I m4
 
 SUBDIRS = man lib mkfs
+if ENABLE_FUSE
+SUBDIRS += fuse
+endif
+
diff --git a/configure.ac b/configure.ac
index bff1e293789a..d5fdfb8a3d17 100644
--- a/configure.ac
+++ b/configure.ac
@@ -63,6 +63,10 @@ AC_ARG_ENABLE(lz4,
    [AS_HELP_STRING([--disable-lz4], [disable LZ4 compression support @<:@default=enabled@:>@])],
    [enable_lz4="$enableval"], [enable_lz4="yes"])
 
+AC_ARG_ENABLE(fuse,
+   [AS_HELP_STRING([--enable-fuse], [enable erofsfuse @<:@default=no@:>@])],
+   [enable_fuse="$enableval"], [enable_fuse="no"])
+
 AC_ARG_WITH(uuid,
    [AS_HELP_STRING([--without-uuid],
       [Ignore presence of libuuid and disable uuid support @<:@default=enabled@:>@])])
@@ -183,6 +187,20 @@ AS_IF([test "x$with_selinux" != "xno"], [
   LIBS="${saved_LIBS}"
   CPPFLAGS="${saved_CPPFLAGS}"], [have_selinux="no"])
 
+# Configure fuse
+AS_IF([test "x$enable_fuse" != "xno"], [
+  PKG_CHECK_MODULES([libfuse], [fuse >= 2.6])
+  # Paranoia: don't trust the result reported by pkgconfig before trying out
+  saved_LIBS="$LIBS"
+  saved_CPPFLAGS=${CPPFLAGS}
+  CPPFLAGS="${libfuse_CFLAGS} ${CPPFLAGS}"
+  LIBS="${libfuse_LIBS} $LIBS"
+  AC_CHECK_LIB(fuse, fuse_main, [
+    have_fuse="yes" ], [
+    AC_MSG_ERROR([libfuse (>= 2.6) doesn't work properly])])
+  LIBS="${saved_LIBS}"
+  CPPFLAGS="${saved_CPPFLAGS}"], [have_fuse="no"])
+
 # Configure lz4
 test -z $LZ4_LIBS && LZ4_LIBS='-llz4'
 
@@ -218,6 +236,7 @@ fi
 # Set up needed symbols, conditionals and compiler/linker flags
 AM_CONDITIONAL([ENABLE_LZ4], [test "x${have_lz4}" = "xyes"])
 AM_CONDITIONAL([ENABLE_LZ4HC], [test "x${have_lz4hc}" = "xyes"])
+AM_CONDITIONAL([ENABLE_FUSE], [test "x${have_fuse}" = "xyes"])
 
 if test "x$have_uuid" = "xyes"; then
   AC_DEFINE([HAVE_LIBUUID], 1, [Define to 1 if libuuid is found])
@@ -247,6 +266,7 @@ AC_SUBST([liblz4_LIBS])
 AC_CONFIG_FILES([Makefile
 		 man/Makefile
 		 lib/Makefile
-		 mkfs/Makefile])
+		 mkfs/Makefile
+		 fuse/Makefile])
 AC_OUTPUT
 
diff --git a/fuse/Makefile.am b/fuse/Makefile.am
new file mode 100644
index 000000000000..6636ee1aec69
--- /dev/null
+++ b/fuse/Makefile.am
@@ -0,0 +1,10 @@
+# SPDX-License-Identifier: GPL-2.0+
+# Makefile.am
+
+AUTOMAKE_OPTIONS = foreign
+bin_PROGRAMS     = erofsfuse
+erofsfuse_SOURCES = dir.c main.c
+erofsfuse_CFLAGS = -Wall -Werror -I$(top_srcdir)/include
+erofsfuse_CFLAGS += -DFUSE_USE_VERSION=26 ${libfuse_CFLAGS}
+erofsfuse_LDADD = $(top_builddir)/lib/liberofs.la ${libfuse_LIBS} ${LZ4_LIBS}
+
diff --git a/fuse/dir.c b/fuse/dir.c
new file mode 100644
index 000000000000..f8fa0f6616a6
--- /dev/null
+++ b/fuse/dir.c
@@ -0,0 +1,103 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * erofs-utils/fuse/dir.c
+ *
+ * Created by Li Guifu <blucerlee@gmail.com>
+ */
+#include <fuse.h>
+#include <fuse_opt.h>
+
+#include "erofs/internal.h"
+#include "erofs/print.h"
+
+static int erofs_fill_dentries(struct erofs_inode *dir,
+			       fuse_fill_dir_t filler, void *buf,
+			       void *dblk, unsigned int nameoff,
+			       unsigned int maxsize)
+{
+	struct erofs_dirent *de = dblk;
+	const struct erofs_dirent *end = dblk + nameoff;
+	char namebuf[EROFS_NAME_LEN + 1];
+
+	while (de < end) {
+		const char *de_name;
+		unsigned int de_namelen;
+
+		nameoff = le16_to_cpu(de->nameoff);
+		de_name = (char *)dblk + nameoff;
+
+		/* the last dirent in the block? */
+		if (de + 1 >= end)
+			de_namelen = strnlen(de_name, maxsize - nameoff);
+		else
+			de_namelen = le16_to_cpu(de[1].nameoff) - nameoff;
+
+		/* a corrupted entry is found */
+		if (nameoff + de_namelen > maxsize ||
+		    de_namelen > EROFS_NAME_LEN) {
+			erofs_err("bogus dirent @ nid %llu", dir->nid | 0ULL);
+			DBG_BUGON(1);
+			return -EFSCORRUPTED;
+		}
+
+		memcpy(namebuf, de_name, de_namelen);
+		namebuf[de_namelen] = '\0';
+
+		filler(buf, namebuf, NULL, 0);
+		++de;
+	}
+	return 0;
+}
+
+int erofsfuse_readdir(const char *path, void *buf, fuse_fill_dir_t filler,
+		      off_t offset, struct fuse_file_info *fi)
+{
+	int ret;
+	struct erofs_inode dir;
+	char dblk[EROFS_BLKSIZ];
+	erofs_off_t pos;
+
+	erofs_dbg("readdir:%s offset=%llu", path, (long long)offset);
+
+	ret = erofs_ilookup(path, &dir);
+	if (ret)
+		return ret;
+
+	erofs_dbg("path=%s nid = %llu", path, dir.nid | 0ULL);
+
+	if (!S_ISDIR(dir.i_mode))
+		return -ENOTDIR;
+
+	if (!dir.i_size)
+		return 0;
+
+	pos = 0;
+	while (pos < dir.i_size) {
+		unsigned int nameoff, maxsize;
+		struct erofs_dirent *de;
+
+		maxsize = min_t(unsigned int, EROFS_BLKSIZ,
+				dir.i_size - pos);
+		ret = erofs_pread(&dir, dblk, maxsize, pos);
+		if (ret)
+			return ret;
+
+		de = (struct erofs_dirent *)dblk;
+		nameoff = le16_to_cpu(de->nameoff);
+		if (nameoff < sizeof(struct erofs_dirent) ||
+		    nameoff >= PAGE_SIZE) {
+			erofs_err("invalid de[0].nameoff %u @ nid %llu",
+				  nameoff, dir.nid | 0ULL);
+			ret = -EFSCORRUPTED;
+			break;
+		}
+
+		ret = erofs_fill_dentries(&dir, filler, buf,
+					  dblk, nameoff, maxsize);
+		if (ret)
+			break;
+		pos += maxsize;
+	}
+	return 0;
+}
+
diff --git a/fuse/main.c b/fuse/main.c
new file mode 100644
index 000000000000..ab8a90aadf8a
--- /dev/null
+++ b/fuse/main.c
@@ -0,0 +1,230 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * erofs-utils/fuse/main.c
+ *
+ * Created by Li Guifu <blucerlee@gmail.com>
+ */
+#include <stdlib.h>
+#include <string.h>
+#include <execinfo.h>
+#include <signal.h>
+#include <libgen.h>
+#include <fuse.h>
+#include <fuse_opt.h>
+
+#include "erofs/config.h"
+#include "erofs/print.h"
+#include "erofs/io.h"
+
+int erofsfuse_readdir(const char *path, void *buffer, fuse_fill_dir_t filler,
+		      off_t offset, struct fuse_file_info *fi);
+
+static void *erofsfuse_init(struct fuse_conn_info *info)
+{
+	erofs_info("Using FUSE protocol %d.%d", info->proto_major, info->proto_minor);
+	return NULL;
+}
+
+static int erofsfuse_open(const char *path, struct fuse_file_info *fi)
+{
+	erofs_dbg("open path=%s", path);
+
+	if ((fi->flags & O_ACCMODE) != O_RDONLY)
+		return -EACCES;
+
+	return 0;
+}
+
+static int erofsfuse_getattr(const char *path, struct stat *stbuf)
+{
+	struct erofs_inode vi = {};
+	int ret;
+
+	erofs_dbg("getattr(%s)", path);
+	ret = erofs_ilookup(path, &vi);
+	if (ret)
+		return -ENOENT;
+
+	stbuf->st_mode  = vi.i_mode;
+	stbuf->st_nlink = vi.i_nlink;
+	stbuf->st_size  = vi.i_size;
+	stbuf->st_blocks = roundup(vi.i_size, EROFS_BLKSIZ) >> 9;
+	stbuf->st_uid = vi.i_uid;
+	stbuf->st_gid = vi.i_gid;
+	if (S_ISBLK(vi.i_mode) || S_ISCHR(vi.i_mode))
+		stbuf->st_rdev = vi.u.i_rdev;
+	stbuf->st_ctime = vi.i_ctime;
+	stbuf->st_mtime = stbuf->st_ctime;
+	stbuf->st_atime = stbuf->st_ctime;
+	return 0;
+}
+
+static int erofsfuse_read(const char *path, char *buffer,
+			  size_t size, off_t offset,
+			  struct fuse_file_info *fi)
+{
+	int ret;
+	struct erofs_inode vi;
+
+	erofs_dbg("path:%s size=%zd offset=%llu", path, size, (long long)offset);
+
+	ret = erofs_ilookup(path, &vi);
+	if (ret)
+		return ret;
+
+	ret = erofs_pread(&vi, buffer, size, offset);
+	if (ret)
+		return ret;
+	return size;
+}
+
+static struct fuse_operations erofs_ops = {
+	.getattr = erofsfuse_getattr,
+	.readdir = erofsfuse_readdir,
+	.open = erofsfuse_open,
+	.read = erofsfuse_read,
+	.init = erofsfuse_init,
+};
+
+static struct options {
+	const char *disk;
+	const char *mountpoint;
+	unsigned int debug_lvl;
+	bool show_help;
+	bool odebug;
+} fusecfg;
+
+#define OPTION(t, p)                           \
+    { t, offsetof(struct options, p), 1 }
+static const struct fuse_opt option_spec[] = {
+	OPTION("--dbglevel=%u", debug_lvl),
+	OPTION("--help", show_help),
+	FUSE_OPT_END
+};
+
+#define OPTION(t, p)    { t, offsetof(struct options, p), 1 }
+
+static void usage(void)
+{
+	struct fuse_args args = FUSE_ARGS_INIT(0, NULL);
+
+	fputs("usage: [options] IMAGE MOUNTPOINT\n\n"
+	      "Options:\n"
+	      "    --dbglevel=#           set output message level to # (maximum 9)\n"
+#if FUSE_MAJOR_VERSION < 3
+	      "    --help                 display this help and exit\n"
+#endif
+	      "\n", stderr);
+
+#if FUSE_MAJOR_VERSION >= 3
+	fuse_cmdline_help();
+#else
+	fuse_opt_add_arg(&args, ""); /* progname */
+	fuse_opt_add_arg(&args, "-ho"); /* progname */
+	fuse_parse_cmdline(&args, NULL, NULL, NULL);
+#endif
+	exit(EXIT_FAILURE);
+}
+
+static void erofsfuse_dumpcfg(void)
+{
+	erofs_dump("disk: %s\n", fusecfg.disk);
+	erofs_dump("mountpoint: %s\n", fusecfg.mountpoint);
+	erofs_dump("dbglevel: %u\n", cfg.c_dbg_lvl);
+}
+
+static int optional_opt_func(void *data, const char *arg, int key,
+			     struct fuse_args *outargs)
+{
+	switch (key) {
+	case FUSE_OPT_KEY_NONOPT:
+		if (fusecfg.mountpoint)
+			return -1; /* Too many args */
+
+		if (!fusecfg.disk) {
+			fusecfg.disk = strdup(arg);
+			return 0;
+		}
+		if (!fusecfg.mountpoint)
+			fusecfg.mountpoint = strdup(arg);
+	case FUSE_OPT_KEY_OPT:
+		if (!strcmp(arg, "-d"))
+			fusecfg.odebug = true;
+		break;
+	default:
+		DBG_BUGON(1);
+		break;
+	}
+	return 1;
+}
+
+static void signal_handle_sigsegv(int signal)
+{
+	void *array[10];
+	size_t nptrs;
+	char **strings;
+	size_t i;
+
+	erofs_dump("========================================\n");
+	erofs_dump("Segmentation Fault.  Starting backtrace:\n");
+	nptrs = backtrace(array, 10);
+	strings = backtrace_symbols(array, nptrs);
+	if (strings) {
+		for (i = 0; i < nptrs; i++)
+			erofs_dump("%s\n", strings[i]);
+		free(strings);
+	}
+	erofs_dump("========================================\n");
+	abort();
+}
+
+
+int main(int argc, char *argv[])
+{
+	int ret;
+	struct fuse_args args = FUSE_ARGS_INIT(argc, argv);
+
+	erofs_init_configure();
+	fprintf(stderr, "%s %s\n", basename(argv[0]), cfg.c_version);
+
+	if (signal(SIGSEGV, signal_handle_sigsegv) == SIG_ERR) {
+		fprintf(stderr, "failed to initialize signals\n");
+		ret = -errno;
+		goto err;
+	}
+
+	/* parse options */
+	ret = fuse_opt_parse(&args, &fusecfg, option_spec, optional_opt_func);
+	if (ret)
+		goto err;
+
+	if (fusecfg.show_help || !fusecfg.mountpoint)
+		usage();
+	cfg.c_dbg_lvl = fusecfg.debug_lvl;
+
+	if (fusecfg.odebug && cfg.c_dbg_lvl < EROFS_DBG)
+		cfg.c_dbg_lvl = EROFS_DBG;
+
+	erofsfuse_dumpcfg();
+	ret = dev_open_ro(fusecfg.disk);
+	if (ret) {
+		fprintf(stderr, "failed to open: %s\n", fusecfg.disk);
+		goto err_fuse_free_args;
+	}
+
+	ret = erofs_read_superblock();
+	if (ret) {
+		fprintf(stderr, "failed to read erofs super block\n");
+		goto err_dev_close;
+	}
+
+	ret = fuse_main(args.argc, args.argv, &erofs_ops, NULL);
+err_dev_close:
+	dev_close();
+err_fuse_free_args:
+	fuse_opt_free_args(&args);
+err:
+	erofs_exit_configure();
+	return ret ? EXIT_FAILURE : EXIT_SUCCESS;
+}
+
diff --git a/include/erofs/internal.h b/include/erofs/internal.h
index cabb2faa0072..ec2646c23b78 100644
--- a/include/erofs/internal.h
+++ b/include/erofs/internal.h
@@ -36,6 +36,8 @@ typedef unsigned short umode_t;
 #error incompatible PAGE_SIZE is already defined
 #endif
 
+#define PAGE_MASK		(~(PAGE_SIZE-1))
+
 #define LOG_BLOCK_SIZE          (12)
 #define EROFS_BLKSIZ            (1U << LOG_BLOCK_SIZE)
 
@@ -59,6 +61,8 @@ typedef u32 erofs_blk_t;
 struct erofs_buffer_head;
 
 struct erofs_sb_info {
+	u64 blocks;
+
 	erofs_blk_t meta_blkaddr;
 	erofs_blk_t xattr_blkaddr;
 
@@ -66,12 +70,25 @@ struct erofs_sb_info {
 	u32 feature_incompat;
 	u64 build_time;
 	u32 build_time_nsec;
+
+	unsigned char islotbits;
+
+	/* what we really care is nid, rather than ino.. */
+	erofs_nid_t root_nid;
+	/* used for statfs, f_files - f_favail */
+	u64 inos;
+
 	u8 uuid[16];
 };
 
 /* global sbi */
 extern struct erofs_sb_info sbi;
 
+static inline erofs_off_t iloc(erofs_nid_t nid)
+{
+	return blknr_to_addr(sbi.meta_blkaddr) + (nid << sbi.islotbits);
+}
+
 #define EROFS_FEATURE_FUNCS(name, compat, feature) \
 static inline bool erofs_sb_has_##name(void) \
 { \
@@ -126,7 +143,16 @@ struct erofs_inode {
 	struct erofs_buffer_head *bh_inline, *bh_data;
 
 	void *idata;
-	void *compressmeta;
+
+	union {
+		void *compressmeta;
+		struct {
+			uint16_t z_advise;
+			uint8_t  z_algorithmtype[2];
+			uint8_t  z_logical_clusterbits;
+			uint8_t  z_physical_clusterbits[2];
+		};
+	};
 #ifdef WITH_ANDROID
 	uint64_t capabilities;
 #endif
@@ -137,6 +163,24 @@ static inline bool is_inode_layout_compression(struct erofs_inode *inode)
 	return erofs_inode_is_data_compressed(inode->datalayout);
 }
 
+static inline unsigned int erofs_bitrange(unsigned int value, unsigned int bit,
+					  unsigned int bits)
+{
+	return (value >> bit) & ((1 << bits) - 1);
+}
+
+static inline unsigned int erofs_inode_version(unsigned int value)
+{
+	return erofs_bitrange(value, EROFS_I_VERSION_BIT,
+			      EROFS_I_VERSION_BITS);
+}
+
+static inline unsigned int erofs_inode_datalayout(unsigned int value)
+{
+	return erofs_bitrange(value, EROFS_I_DATALAYOUT_BIT,
+			      EROFS_I_DATALAYOUT_BITS);
+}
+
 #define IS_ROOT(x)	((x) == (x)->i_parent)
 
 struct erofs_dentry {
@@ -169,5 +213,43 @@ static inline const char *erofs_strerror(int err)
 	return msg;
 }
 
+enum {
+	BH_Meta,
+	BH_Mapped,
+	BH_Zipped,
+	BH_FullMapped,
+};
+
+/* Has a disk mapping */
+#define EROFS_MAP_MAPPED	(1 << BH_Mapped)
+/* Located in metadata (could be copied from bd_inode) */
+#define EROFS_MAP_META		(1 << BH_Meta)
+/* The extent has been compressed */
+#define EROFS_MAP_ZIPPED	(1 << BH_Zipped)
+/* The length of extent is full */
+#define EROFS_MAP_FULL_MAPPED	(1 << BH_FullMapped)
+
+struct erofs_map_blocks {
+	char mpage[EROFS_BLKSIZ];
+
+	erofs_off_t m_pa, m_la;
+	u64 m_plen, m_llen;
+
+	unsigned int m_flags;
+	erofs_blk_t index;
+};
+
+/* super.c */
+int erofs_read_superblock(void);
+
+/* namei.c */
+int erofs_ilookup(const char *path, struct erofs_inode *vi);
+
+/* data.c */
+int erofs_pread(struct erofs_inode *inode, char *buf,
+		erofs_off_t count, erofs_off_t offset);
+
+#define EFSCORRUPTED	EUCLEAN		/* Filesystem is corrupted */
+
 #endif
 
diff --git a/include/erofs/io.h b/include/erofs/io.h
index a23de64541c6..557424578ece 100644
--- a/include/erofs/io.h
+++ b/include/erofs/io.h
@@ -17,6 +17,7 @@
 #endif
 
 int dev_open(const char *devname);
+int dev_open_ro(const char *dev);
 void dev_close(void);
 int dev_write(const void *buf, u64 offset, size_t len);
 int dev_read(void *buf, u64 offset, size_t len);
diff --git a/include/erofs/trace.h b/include/erofs/trace.h
new file mode 100644
index 000000000000..5a12da753d70
--- /dev/null
+++ b/include/erofs/trace.h
@@ -0,0 +1,14 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * erofs-utils/include/erofs/trace.h
+ *
+ * Copyright (C) 2020 Gao Xiang <hsiangkao@aol.com>
+ */
+#ifndef __EROFS_TRACE_H
+#define __EROFS_TRACE_H
+
+#define trace_erofs_map_blocks_flatmode_enter(inode, map, flags) ((void)0)
+#define trace_erofs_map_blocks_flatmode_exit(inode, map, flags, ret) ((void)0)
+
+#endif
+
diff --git a/include/erofs_fs.h b/include/erofs_fs.h
index 4cd79f01d820..a69f179a51a5 100644
--- a/include/erofs_fs.h
+++ b/include/erofs_fs.h
@@ -279,6 +279,10 @@ struct z_erofs_vle_decompressed_index {
 	} di_u;
 };
 
+#define Z_EROFS_VLE_LEGACY_INDEX_ALIGN(size) \
+	(round_up(size, sizeof(struct z_erofs_vle_decompressed_index)) + \
+	 sizeof(struct z_erofs_map_header) + Z_EROFS_VLE_LEGACY_HEADER_PADDING)
+
 #define Z_EROFS_VLE_EXTENT_ALIGN(size) round_up(size, \
 	sizeof(struct z_erofs_vle_decompressed_index))
 
diff --git a/lib/Makefile.am b/lib/Makefile.am
index e4b51e65f053..e1c43fa89009 100644
--- a/lib/Makefile.am
+++ b/lib/Makefile.am
@@ -2,8 +2,8 @@
 # Makefile.am
 
 noinst_LTLIBRARIES = liberofs.la
-liberofs_la_SOURCES = config.c io.c cache.c inode.c xattr.c \
-		      compress.c compressor.c exclude.c
+liberofs_la_SOURCES = config.c io.c cache.c super.c inode.c xattr.c exclude.c \
+		      namei.c data.c compress.c compressor.c
 liberofs_la_CFLAGS = -Wall -Werror -I$(top_srcdir)/include
 if ENABLE_LZ4
 liberofs_la_CFLAGS += ${LZ4_CFLAGS}
diff --git a/lib/data.c b/lib/data.c
new file mode 100644
index 000000000000..0337521f560e
--- /dev/null
+++ b/lib/data.c
@@ -0,0 +1,134 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * erofs-utils/lib/data.c
+ *
+ * Copyright (C) 2020 Gao Xiang <hsiangkao@aol.com>
+ * Compression support by Huang Jianan <huangjianan@oppo.com>
+ */
+#include "erofs/print.h"
+#include "erofs/internal.h"
+#include "erofs/io.h"
+#include "erofs/trace.h"
+
+static int erofs_map_blocks_flatmode(struct erofs_inode *inode,
+				     struct erofs_map_blocks *map,
+				     int flags)
+{
+	int err = 0;
+	erofs_blk_t nblocks, lastblk;
+	u64 offset = map->m_la;
+	struct erofs_inode *vi = inode;
+	bool tailendpacking = (vi->datalayout == EROFS_INODE_FLAT_INLINE);
+
+	trace_erofs_map_blocks_flatmode_enter(inode, map, flags);
+
+	nblocks = DIV_ROUND_UP(inode->i_size, PAGE_SIZE);
+	lastblk = nblocks - tailendpacking;
+
+	if (offset >= inode->i_size) {
+		/* leave out-of-bound access unmapped */
+		map->m_flags = 0;
+		goto out;
+	}
+
+	/* there is no hole in flatmode */
+	map->m_flags = EROFS_MAP_MAPPED;
+
+	if (offset < blknr_to_addr(lastblk)) {
+		map->m_pa = blknr_to_addr(vi->u.i_blkaddr) + map->m_la;
+		map->m_plen = blknr_to_addr(lastblk) - offset;
+	} else if (tailendpacking) {
+		/* 2 - inode inline B: inode, [xattrs], inline last blk... */
+		map->m_pa = iloc(vi->nid) + vi->inode_isize +
+			vi->xattr_isize + erofs_blkoff(map->m_la);
+		map->m_plen = inode->i_size - offset;
+
+		/* inline data should be located in one meta block */
+		if (erofs_blkoff(map->m_pa) + map->m_plen > PAGE_SIZE) {
+			erofs_err("inline data cross block boundary @ nid %" PRIu64,
+				  vi->nid);
+			DBG_BUGON(1);
+			err = -EFSCORRUPTED;
+			goto err_out;
+		}
+
+		map->m_flags |= EROFS_MAP_META;
+	} else {
+		erofs_err("internal error @ nid: %" PRIu64 " (size %llu), m_la 0x%" PRIx64,
+			  vi->nid, (unsigned long long)inode->i_size, map->m_la);
+		DBG_BUGON(1);
+		err = -EIO;
+		goto err_out;
+	}
+
+out:
+	map->m_llen = map->m_plen;
+
+err_out:
+	trace_erofs_map_blocks_flatmode_exit(inode, map, flags, 0);
+	return err;
+}
+
+static int erofs_read_raw_data(struct erofs_inode *inode, char *buffer,
+			       erofs_off_t size, erofs_off_t offset)
+{
+	struct erofs_map_blocks map = {
+		.index = UINT_MAX,
+	};
+	int ret;
+	erofs_off_t ptr = offset;
+
+	while (ptr < offset + size) {
+		erofs_off_t eend;
+
+		map.m_la = ptr;
+		ret = erofs_map_blocks_flatmode(inode, &map, 0);
+		if (ret)
+			return ret;
+
+		DBG_BUGON(map.m_plen != map.m_llen);
+
+		if (!(map.m_flags & EROFS_MAP_MAPPED)) {
+			if (!map.m_llen) {
+				ptr = offset + size;
+				continue;
+			}
+			ptr = map.m_la + map.m_llen;
+			continue;
+		}
+
+		/* trim extent */
+		eend = min(offset + size, map.m_la + map.m_llen);
+		DBG_BUGON(ptr < map.m_la);
+
+		if (ptr > map.m_la) {
+			map.m_pa += ptr - map.m_la;
+			map.m_la = ptr;
+		}
+
+		ret = dev_read(buffer + ptr - offset,
+			       map.m_pa, eend - map.m_la);
+		if (ret < 0)
+			return -EIO;
+
+		ptr = eend;
+	}
+	return 0;
+}
+
+int erofs_pread(struct erofs_inode *inode, char *buf,
+		erofs_off_t count, erofs_off_t offset)
+{
+	switch (inode->datalayout) {
+	case EROFS_INODE_FLAT_PLAIN:
+	case EROFS_INODE_FLAT_INLINE:
+		return erofs_read_raw_data(inode, buf, count, offset);
+	case EROFS_INODE_FLAT_COMPRESSION_LEGACY:
+	case EROFS_INODE_FLAT_COMPRESSION:
+		return -EOPNOTSUPP;
+	default:
+		break;
+	}
+	return -EINVAL;
+}
+
diff --git a/lib/io.c b/lib/io.c
index 4f5d9a6edaa4..d835f34da50f 100644
--- a/lib/io.c
+++ b/lib/io.c
@@ -108,6 +108,22 @@ int dev_open(const char *dev)
 	return 0;
 }
 
+/* XXX: temporary soluation. Disk I/O implementation needs to be refactored. */
+int dev_open_ro(const char *dev)
+{
+	int fd = open(dev, O_RDONLY | O_BINARY);
+
+	if (fd < 0) {
+		erofs_err("failed to open(%s).", dev);
+		return -errno;
+	}
+
+	erofs_devfd = fd;
+	erofs_devname = dev;
+	erofs_devsz = INT64_MAX;
+	return 0;
+}
+
 u64 dev_length(void)
 {
 	return erofs_devsz;
diff --git a/lib/namei.c b/lib/namei.c
new file mode 100644
index 000000000000..b05f5c421d54
--- /dev/null
+++ b/lib/namei.c
@@ -0,0 +1,246 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * erofs-utils/lib/namei.c
+ *
+ * Created by Li Guifu <blucerlee@gmail.com>
+ */
+#include <linux/kdev_t.h>
+#include <sys/types.h>
+#include <unistd.h>
+#include <stdio.h>
+#include <errno.h>
+#include <sys/stat.h>
+#include <sys/sysmacros.h>
+
+#include "erofs/print.h"
+#include "erofs/io.h"
+
+static int erofs_read_inode_from_disk(struct erofs_inode *vi)
+{
+	int ret, ifmt;
+	char buf[sizeof(struct erofs_inode_extended)];
+	struct erofs_inode_compact *dic;
+	struct erofs_inode_extended *die;
+	const erofs_off_t inode_loc = iloc(vi->nid);
+
+	ret = dev_read(buf, inode_loc, sizeof(*dic));
+	if (ret < 0)
+		return -EIO;
+
+	dic = (struct erofs_inode_compact *)buf;
+	ifmt = le16_to_cpu(dic->i_format);
+
+	vi->datalayout = erofs_inode_datalayout(ifmt);
+	if (vi->datalayout >= EROFS_INODE_DATALAYOUT_MAX) {
+		erofs_err("unsupported datalayout %u of nid %llu",
+			  vi->datalayout, vi->nid | 0ULL);
+		return -EOPNOTSUPP;
+	}
+	switch (erofs_inode_version(ifmt)) {
+	case EROFS_INODE_LAYOUT_EXTENDED:
+		vi->inode_isize = sizeof(struct erofs_inode_extended);
+
+		ret = dev_read(buf + sizeof(*dic), inode_loc + sizeof(*dic),
+			       sizeof(*die) - sizeof(*dic));
+		if (ret < 0)
+			return -EIO;
+
+		die = (struct erofs_inode_extended *)buf;
+		vi->xattr_isize = erofs_xattr_ibody_size(die->i_xattr_icount);
+		vi->i_mode = le16_to_cpu(die->i_mode);
+
+		switch (vi->i_mode & S_IFMT) {
+		case S_IFREG:
+		case S_IFDIR:
+		case S_IFLNK:
+			vi->u.i_blkaddr = le32_to_cpu(die->i_u.raw_blkaddr);
+			break;
+		case S_IFCHR:
+		case S_IFBLK:
+			return -EOPNOTSUPP;
+		case S_IFIFO:
+		case S_IFSOCK:
+			return -EOPNOTSUPP;
+		default:
+			goto bogusimode;
+		}
+
+		vi->i_uid = le32_to_cpu(die->i_uid);
+		vi->i_gid = le32_to_cpu(die->i_gid);
+		vi->i_nlink = le32_to_cpu(die->i_nlink);
+
+		vi->i_ctime = le64_to_cpu(die->i_ctime);
+		vi->i_ctime_nsec = le64_to_cpu(die->i_ctime_nsec);
+		vi->i_size = le64_to_cpu(die->i_size);
+		break;
+	case EROFS_INODE_LAYOUT_COMPACT:
+		vi->inode_isize = sizeof(struct erofs_inode_compact);
+		vi->xattr_isize = erofs_xattr_ibody_size(dic->i_xattr_icount);
+		vi->i_mode = le16_to_cpu(dic->i_mode);
+
+		switch (vi->i_mode & S_IFMT) {
+		case S_IFREG:
+		case S_IFDIR:
+		case S_IFLNK:
+			vi->u.i_blkaddr = le32_to_cpu(dic->i_u.raw_blkaddr);
+			break;
+		case S_IFCHR:
+		case S_IFBLK:
+			return -EOPNOTSUPP;
+		case S_IFIFO:
+		case S_IFSOCK:
+			return -EOPNOTSUPP;
+		default:
+			goto bogusimode;
+		}
+
+		vi->i_uid = le16_to_cpu(dic->i_uid);
+		vi->i_gid = le16_to_cpu(dic->i_gid);
+		vi->i_nlink = le16_to_cpu(dic->i_nlink);
+
+		vi->i_ctime = sbi.build_time;
+		vi->i_ctime_nsec = sbi.build_time_nsec;
+
+		vi->i_size = le32_to_cpu(dic->i_size);
+		break;
+	default:
+		erofs_err("unsupported on-disk inode version %u of nid %llu",
+			  erofs_inode_version(ifmt), vi->nid | 0ULL);
+		return -EOPNOTSUPP;
+	}
+	return 0;
+bogusimode:
+	erofs_err("bogus i_mode (%o) @ nid %llu", vi->i_mode, vi->nid | 0ULL);
+	return -EFSCORRUPTED;
+}
+
+
+struct erofs_dirent *find_target_dirent(erofs_nid_t pnid,
+					void *dentry_blk,
+					const char *name, unsigned int len,
+					unsigned int nameoff,
+					unsigned int maxsize)
+{
+	struct erofs_dirent *de = dentry_blk;
+	const struct erofs_dirent *end = dentry_blk + nameoff;
+
+	while (de < end) {
+		const char *de_name;
+		unsigned int de_namelen;
+
+		nameoff = le16_to_cpu(de->nameoff);
+		de_name = (char *)dentry_blk + nameoff;
+
+		/* the last dirent in the block? */
+		if (de + 1 >= end)
+			de_namelen = strnlen(de_name, maxsize - nameoff);
+		else
+			de_namelen = le16_to_cpu(de[1].nameoff) - nameoff;
+
+		/* a corrupted entry is found */
+		if (nameoff + de_namelen > maxsize ||
+		    de_namelen > EROFS_NAME_LEN) {
+			erofs_err("bogus dirent @ nid %llu", pnid | 0ULL);
+			DBG_BUGON(1);
+			return ERR_PTR(-EFSCORRUPTED);
+		}
+
+		if (len == de_namelen && !memcmp(de_name, name, de_namelen))
+			return de;
+		++de;
+	}
+	return NULL;
+}
+
+struct nameidata {
+	erofs_nid_t	nid;
+	unsigned int	ftype;
+};
+
+int erofs_namei(struct nameidata *nd,
+		const char *name, unsigned int len)
+{
+	erofs_nid_t nid = nd->nid;
+	int ret;
+	char buf[EROFS_BLKSIZ];
+	struct erofs_inode vi = { .nid = nid };
+	erofs_off_t offset;
+
+	ret = erofs_read_inode_from_disk(&vi);
+	if (ret)
+		return ret;
+
+	offset = 0;
+	while (offset < vi.i_size) {
+		erofs_off_t maxsize = min_t(erofs_off_t,
+					    vi.i_size - offset, EROFS_BLKSIZ);
+		struct erofs_dirent *de = (void *)buf;
+		unsigned int nameoff;
+
+		ret = erofs_pread(&vi, buf, maxsize, offset);
+		if (ret)
+			return ret;
+
+		nameoff = le16_to_cpu(de->nameoff);
+		if (nameoff < sizeof(struct erofs_dirent) ||
+		    nameoff >= PAGE_SIZE) {
+			erofs_err("invalid de[0].nameoff %u @ nid %llu",
+				  nameoff, nid | 0ULL);
+			return -EFSCORRUPTED;
+		}
+
+		de = find_target_dirent(nid, buf, name, len,
+					nameoff, maxsize);
+		if (IS_ERR(de))
+			return PTR_ERR(de);
+
+		if (de) {
+			nd->nid = le64_to_cpu(de->nid);
+			return 0;
+		}
+		offset += maxsize;
+	}
+	return -ENOENT;
+}
+
+static int link_path_walk(const char *name, struct nameidata *nd)
+{
+	nd->nid = sbi.root_nid;
+
+	while (*name == '/')
+		name++;
+
+	/* At this point we know we have a real path component. */
+	while (*name != '\0') {
+		const char *p = name;
+		int ret;
+
+		do {
+			++p;
+		} while (*p != '\0' && *p != '/');
+
+		DBG_BUGON(p <= name);
+		ret = erofs_namei(nd, name, p - name);
+		if (ret)
+			return ret;
+
+		name = p;
+		/* Skip until no more slashes. */
+		for (name = p; *name == '/'; ++name);
+	}
+	return 0;
+}
+
+int erofs_ilookup(const char *path, struct erofs_inode *vi)
+{
+	int ret;
+	struct nameidata nd;
+
+	ret = link_path_walk(path, &nd);
+	if (ret)
+		return ret;
+
+	vi->nid = nd.nid;
+	return erofs_read_inode_from_disk(vi);
+}
+
diff --git a/lib/super.c b/lib/super.c
new file mode 100644
index 000000000000..2d366928e12b
--- /dev/null
+++ b/lib/super.c
@@ -0,0 +1,78 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * erofs-utils/lib/super.c
+ *
+ * Created by Li Guifu <blucerlee@gmail.com>
+ */
+#include <string.h>
+#include <stdlib.h>
+#include <asm-generic/errno-base.h>
+
+#include "erofs/io.h"
+#include "erofs/print.h"
+
+struct erofs_sb_info sbi;
+
+static bool check_layout_compatibility(struct erofs_sb_info *sbi,
+				       struct erofs_super_block *dsb)
+{
+	const unsigned int feature = le32_to_cpu(dsb->feature_incompat);
+
+	sbi->feature_incompat = feature;
+
+	/* check if current kernel meets all mandatory requirements */
+	if (feature & (~EROFS_ALL_FEATURE_INCOMPAT)) {
+		erofs_err("unidentified incompatible feature %x, please upgrade kernel version",
+			  feature & ~EROFS_ALL_FEATURE_INCOMPAT);
+		return false;
+	}
+	return true;
+}
+
+int erofs_read_superblock(void)
+{
+	char data[EROFS_BLKSIZ];
+	struct erofs_super_block *dsb;
+	unsigned int blkszbits;
+	int ret;
+
+	ret = blk_read(data, 0, 1);
+	if (ret < 0) {
+		erofs_err("cannot read erofs superblock: %d", ret);
+		return -EIO;
+	}
+	dsb = (struct erofs_super_block *)(data + EROFS_SUPER_OFFSET);
+
+	ret = -EINVAL;
+	if (le32_to_cpu(dsb->magic) != EROFS_SUPER_MAGIC_V1) {
+		erofs_err("cannot find valid erofs superblock");
+		return ret;
+	}
+
+	sbi.feature_compat = le32_to_cpu(dsb->feature_compat);
+
+	blkszbits = dsb->blkszbits;
+	/* 9(512 bytes) + LOG_SECTORS_PER_BLOCK == LOG_BLOCK_SIZE */
+	if (blkszbits != LOG_BLOCK_SIZE) {
+		erofs_err("blksize %u isn't supported on this platform",
+			  1 << blkszbits);
+		return ret;
+	}
+
+	if (!check_layout_compatibility(&sbi, dsb))
+		return ret;
+
+	sbi.blocks = le32_to_cpu(dsb->blocks);
+	sbi.meta_blkaddr = le32_to_cpu(dsb->meta_blkaddr);
+	sbi.xattr_blkaddr = le32_to_cpu(dsb->xattr_blkaddr);
+	sbi.islotbits = EROFS_ISLOTBITS;
+	sbi.root_nid = le16_to_cpu(dsb->root_nid);
+	sbi.inos = le64_to_cpu(dsb->inos);
+
+	sbi.build_time = le64_to_cpu(dsb->build_time);
+	sbi.build_time_nsec = le32_to_cpu(dsb->build_time_nsec);
+
+	memcpy(&sbi.uuid, dsb->uuid, sizeof(dsb->uuid));
+	return 0;
+}
+
-- 
2.24.0

[PATCH v4 1/3] erofs-utils: introduce fuse implementation

[Gao Xiang via Linux-erofs]

From: Li Guifu <blucerlee@gmail.com>

Let's add a simple erofsfuse approach, and benefits are:

 - images can be supported on various platforms;
 - new unpack tool can be developed based on this;
 - new on-disk features can be iterated, verified effectively.

This commit only addresses reading uncompressed regular files.
Other file (e.g. compressed file) support is out of scope here.

Note that erofsfuse is an unstable feature for now (also notice
LZ4_decompress_safe_partial() was broken in lz4-1.9.2, which
just fixed in lz4-1.9.3), let's disable it by default for a while.

Signed-off-by: Li Guifu <blucerlee@gmail.com>
Signed-off-by: Huang Jianan <huangjianan@oppo.com>
Signed-off-by: Guo Weichao <guoweichao@oppo.com>
Signed-off-by: Gao Xiang <hsiangkao@aol.com>
---
changes since v3:
 - fix build error without lz4 library.

 Makefile.am              |   4 +
 configure.ac             |  22 +++-
 fuse/Makefile.am         |  10 ++
 fuse/dir.c               | 103 ++++++++++++++++
 fuse/main.c              | 230 ++++++++++++++++++++++++++++++++++++
 include/erofs/internal.h |  84 ++++++++++++-
 include/erofs/io.h       |   1 +
 include/erofs/trace.h    |  14 +++
 include/erofs_fs.h       |   4 +
 lib/Makefile.am          |   4 +-
 lib/data.c               | 134 +++++++++++++++++++++
 lib/io.c                 |  16 +++
 lib/namei.c              | 246 +++++++++++++++++++++++++++++++++++++++
 lib/super.c              |  78 +++++++++++++
 14 files changed, 946 insertions(+), 4 deletions(-)
 create mode 100644 fuse/Makefile.am
 create mode 100644 fuse/dir.c
 create mode 100644 fuse/main.c
 create mode 100644 include/erofs/trace.h
 create mode 100644 lib/data.c
 create mode 100644 lib/namei.c
 create mode 100644 lib/super.c

diff --git a/Makefile.am b/Makefile.am
index 1d20577068c5..b804aa90efa9 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -4,3 +4,7 @@
 ACLOCAL_AMFLAGS = -I m4
 
 SUBDIRS = man lib mkfs
+if ENABLE_FUSE
+SUBDIRS += fuse
+endif
+
diff --git a/configure.ac b/configure.ac
index bff1e293789a..d5fdfb8a3d17 100644
--- a/configure.ac
+++ b/configure.ac
@@ -63,6 +63,10 @@ AC_ARG_ENABLE(lz4,
    [AS_HELP_STRING([--disable-lz4], [disable LZ4 compression support @<:@default=enabled@:>@])],
    [enable_lz4="$enableval"], [enable_lz4="yes"])
 
+AC_ARG_ENABLE(fuse,
+   [AS_HELP_STRING([--enable-fuse], [enable erofsfuse @<:@default=no@:>@])],
+   [enable_fuse="$enableval"], [enable_fuse="no"])
+
 AC_ARG_WITH(uuid,
    [AS_HELP_STRING([--without-uuid],
       [Ignore presence of libuuid and disable uuid support @<:@default=enabled@:>@])])
@@ -183,6 +187,20 @@ AS_IF([test "x$with_selinux" != "xno"], [
   LIBS="${saved_LIBS}"
   CPPFLAGS="${saved_CPPFLAGS}"], [have_selinux="no"])
 
+# Configure fuse
+AS_IF([test "x$enable_fuse" != "xno"], [
+  PKG_CHECK_MODULES([libfuse], [fuse >= 2.6])
+  # Paranoia: don't trust the result reported by pkgconfig before trying out
+  saved_LIBS="$LIBS"
+  saved_CPPFLAGS=${CPPFLAGS}
+  CPPFLAGS="${libfuse_CFLAGS} ${CPPFLAGS}"
+  LIBS="${libfuse_LIBS} $LIBS"
+  AC_CHECK_LIB(fuse, fuse_main, [
+    have_fuse="yes" ], [
+    AC_MSG_ERROR([libfuse (>= 2.6) doesn't work properly])])
+  LIBS="${saved_LIBS}"
+  CPPFLAGS="${saved_CPPFLAGS}"], [have_fuse="no"])
+
 # Configure lz4
 test -z $LZ4_LIBS && LZ4_LIBS='-llz4'
 
@@ -218,6 +236,7 @@ fi
 # Set up needed symbols, conditionals and compiler/linker flags
 AM_CONDITIONAL([ENABLE_LZ4], [test "x${have_lz4}" = "xyes"])
 AM_CONDITIONAL([ENABLE_LZ4HC], [test "x${have_lz4hc}" = "xyes"])
+AM_CONDITIONAL([ENABLE_FUSE], [test "x${have_fuse}" = "xyes"])
 
 if test "x$have_uuid" = "xyes"; then
   AC_DEFINE([HAVE_LIBUUID], 1, [Define to 1 if libuuid is found])
@@ -247,6 +266,7 @@ AC_SUBST([liblz4_LIBS])
 AC_CONFIG_FILES([Makefile
 		 man/Makefile
 		 lib/Makefile
-		 mkfs/Makefile])
+		 mkfs/Makefile
+		 fuse/Makefile])
 AC_OUTPUT
 
diff --git a/fuse/Makefile.am b/fuse/Makefile.am
new file mode 100644
index 000000000000..f14f6fd3141b
--- /dev/null
+++ b/fuse/Makefile.am
@@ -0,0 +1,10 @@
+# SPDX-License-Identifier: GPL-2.0+
+# Makefile.am
+
+AUTOMAKE_OPTIONS = foreign
+bin_PROGRAMS     = erofsfuse
+erofsfuse_SOURCES = dir.c main.c
+erofsfuse_CFLAGS = -Wall -Werror -I$(top_srcdir)/include
+erofsfuse_CFLAGS += -DFUSE_USE_VERSION=26 ${libfuse_CFLAGS}
+erofsfuse_LDADD = $(top_builddir)/lib/liberofs.la ${libfuse_LIBS} ${liblz4_LIBS}
+
diff --git a/fuse/dir.c b/fuse/dir.c
new file mode 100644
index 000000000000..f8fa0f6616a6
--- /dev/null
+++ b/fuse/dir.c
@@ -0,0 +1,103 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * erofs-utils/fuse/dir.c
+ *
+ * Created by Li Guifu <blucerlee@gmail.com>
+ */
+#include <fuse.h>
+#include <fuse_opt.h>
+
+#include "erofs/internal.h"
+#include "erofs/print.h"
+
+static int erofs_fill_dentries(struct erofs_inode *dir,
+			       fuse_fill_dir_t filler, void *buf,
+			       void *dblk, unsigned int nameoff,
+			       unsigned int maxsize)
+{
+	struct erofs_dirent *de = dblk;
+	const struct erofs_dirent *end = dblk + nameoff;
+	char namebuf[EROFS_NAME_LEN + 1];
+
+	while (de < end) {
+		const char *de_name;
+		unsigned int de_namelen;
+
+		nameoff = le16_to_cpu(de->nameoff);
+		de_name = (char *)dblk + nameoff;
+
+		/* the last dirent in the block? */
+		if (de + 1 >= end)
+			de_namelen = strnlen(de_name, maxsize - nameoff);
+		else
+			de_namelen = le16_to_cpu(de[1].nameoff) - nameoff;
+
+		/* a corrupted entry is found */
+		if (nameoff + de_namelen > maxsize ||
+		    de_namelen > EROFS_NAME_LEN) {
+			erofs_err("bogus dirent @ nid %llu", dir->nid | 0ULL);
+			DBG_BUGON(1);
+			return -EFSCORRUPTED;
+		}
+
+		memcpy(namebuf, de_name, de_namelen);
+		namebuf[de_namelen] = '\0';
+
+		filler(buf, namebuf, NULL, 0);
+		++de;
+	}
+	return 0;
+}
+
+int erofsfuse_readdir(const char *path, void *buf, fuse_fill_dir_t filler,
+		      off_t offset, struct fuse_file_info *fi)
+{
+	int ret;
+	struct erofs_inode dir;
+	char dblk[EROFS_BLKSIZ];
+	erofs_off_t pos;
+
+	erofs_dbg("readdir:%s offset=%llu", path, (long long)offset);
+
+	ret = erofs_ilookup(path, &dir);
+	if (ret)
+		return ret;
+
+	erofs_dbg("path=%s nid = %llu", path, dir.nid | 0ULL);
+
+	if (!S_ISDIR(dir.i_mode))
+		return -ENOTDIR;
+
+	if (!dir.i_size)
+		return 0;
+
+	pos = 0;
+	while (pos < dir.i_size) {
+		unsigned int nameoff, maxsize;
+		struct erofs_dirent *de;
+
+		maxsize = min_t(unsigned int, EROFS_BLKSIZ,
+				dir.i_size - pos);
+		ret = erofs_pread(&dir, dblk, maxsize, pos);
+		if (ret)
+			return ret;
+
+		de = (struct erofs_dirent *)dblk;
+		nameoff = le16_to_cpu(de->nameoff);
+		if (nameoff < sizeof(struct erofs_dirent) ||
+		    nameoff >= PAGE_SIZE) {
+			erofs_err("invalid de[0].nameoff %u @ nid %llu",
+				  nameoff, dir.nid | 0ULL);
+			ret = -EFSCORRUPTED;
+			break;
+		}
+
+		ret = erofs_fill_dentries(&dir, filler, buf,
+					  dblk, nameoff, maxsize);
+		if (ret)
+			break;
+		pos += maxsize;
+	}
+	return 0;
+}
+
diff --git a/fuse/main.c b/fuse/main.c
new file mode 100644
index 000000000000..ab8a90aadf8a
--- /dev/null
+++ b/fuse/main.c
@@ -0,0 +1,230 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * erofs-utils/fuse/main.c
+ *
+ * Created by Li Guifu <blucerlee@gmail.com>
+ */
+#include <stdlib.h>
+#include <string.h>
+#include <execinfo.h>
+#include <signal.h>
+#include <libgen.h>
+#include <fuse.h>
+#include <fuse_opt.h>
+
+#include "erofs/config.h"
+#include "erofs/print.h"
+#include "erofs/io.h"
+
+int erofsfuse_readdir(const char *path, void *buffer, fuse_fill_dir_t filler,
+		      off_t offset, struct fuse_file_info *fi);
+
+static void *erofsfuse_init(struct fuse_conn_info *info)
+{
+	erofs_info("Using FUSE protocol %d.%d", info->proto_major, info->proto_minor);
+	return NULL;
+}
+
+static int erofsfuse_open(const char *path, struct fuse_file_info *fi)
+{
+	erofs_dbg("open path=%s", path);
+
+	if ((fi->flags & O_ACCMODE) != O_RDONLY)
+		return -EACCES;
+
+	return 0;
+}
+
+static int erofsfuse_getattr(const char *path, struct stat *stbuf)
+{
+	struct erofs_inode vi = {};
+	int ret;
+
+	erofs_dbg("getattr(%s)", path);
+	ret = erofs_ilookup(path, &vi);
+	if (ret)
+		return -ENOENT;
+
+	stbuf->st_mode  = vi.i_mode;
+	stbuf->st_nlink = vi.i_nlink;
+	stbuf->st_size  = vi.i_size;
+	stbuf->st_blocks = roundup(vi.i_size, EROFS_BLKSIZ) >> 9;
+	stbuf->st_uid = vi.i_uid;
+	stbuf->st_gid = vi.i_gid;
+	if (S_ISBLK(vi.i_mode) || S_ISCHR(vi.i_mode))
+		stbuf->st_rdev = vi.u.i_rdev;
+	stbuf->st_ctime = vi.i_ctime;
+	stbuf->st_mtime = stbuf->st_ctime;
+	stbuf->st_atime = stbuf->st_ctime;
+	return 0;
+}
+
+static int erofsfuse_read(const char *path, char *buffer,
+			  size_t size, off_t offset,
+			  struct fuse_file_info *fi)
+{
+	int ret;
+	struct erofs_inode vi;
+
+	erofs_dbg("path:%s size=%zd offset=%llu", path, size, (long long)offset);
+
+	ret = erofs_ilookup(path, &vi);
+	if (ret)
+		return ret;
+
+	ret = erofs_pread(&vi, buffer, size, offset);
+	if (ret)
+		return ret;
+	return size;
+}
+
+static struct fuse_operations erofs_ops = {
+	.getattr = erofsfuse_getattr,
+	.readdir = erofsfuse_readdir,
+	.open = erofsfuse_open,
+	.read = erofsfuse_read,
+	.init = erofsfuse_init,
+};
+
+static struct options {
+	const char *disk;
+	const char *mountpoint;
+	unsigned int debug_lvl;
+	bool show_help;
+	bool odebug;
+} fusecfg;
+
+#define OPTION(t, p)                           \
+    { t, offsetof(struct options, p), 1 }
+static const struct fuse_opt option_spec[] = {
+	OPTION("--dbglevel=%u", debug_lvl),
+	OPTION("--help", show_help),
+	FUSE_OPT_END
+};
+
+#define OPTION(t, p)    { t, offsetof(struct options, p), 1 }
+
+static void usage(void)
+{
+	struct fuse_args args = FUSE_ARGS_INIT(0, NULL);
+
+	fputs("usage: [options] IMAGE MOUNTPOINT\n\n"
+	      "Options:\n"
+	      "    --dbglevel=#           set output message level to # (maximum 9)\n"
+#if FUSE_MAJOR_VERSION < 3
+	      "    --help                 display this help and exit\n"
+#endif
+	      "\n", stderr);
+
+#if FUSE_MAJOR_VERSION >= 3
+	fuse_cmdline_help();
+#else
+	fuse_opt_add_arg(&args, ""); /* progname */
+	fuse_opt_add_arg(&args, "-ho"); /* progname */
+	fuse_parse_cmdline(&args, NULL, NULL, NULL);
+#endif
+	exit(EXIT_FAILURE);
+}
+
+static void erofsfuse_dumpcfg(void)
+{
+	erofs_dump("disk: %s\n", fusecfg.disk);
+	erofs_dump("mountpoint: %s\n", fusecfg.mountpoint);
+	erofs_dump("dbglevel: %u\n", cfg.c_dbg_lvl);
+}
+
+static int optional_opt_func(void *data, const char *arg, int key,
+			     struct fuse_args *outargs)
+{
+	switch (key) {
+	case FUSE_OPT_KEY_NONOPT:
+		if (fusecfg.mountpoint)
+			return -1; /* Too many args */
+
+		if (!fusecfg.disk) {
+			fusecfg.disk = strdup(arg);
+			return 0;
+		}
+		if (!fusecfg.mountpoint)
+			fusecfg.mountpoint = strdup(arg);
+	case FUSE_OPT_KEY_OPT:
+		if (!strcmp(arg, "-d"))
+			fusecfg.odebug = true;
+		break;
+	default:
+		DBG_BUGON(1);
+		break;
+	}
+	return 1;
+}
+
+static void signal_handle_sigsegv(int signal)
+{
+	void *array[10];
+	size_t nptrs;
+	char **strings;
+	size_t i;
+
+	erofs_dump("========================================\n");
+	erofs_dump("Segmentation Fault.  Starting backtrace:\n");
+	nptrs = backtrace(array, 10);
+	strings = backtrace_symbols(array, nptrs);
+	if (strings) {
+		for (i = 0; i < nptrs; i++)
+			erofs_dump("%s\n", strings[i]);
+		free(strings);
+	}
+	erofs_dump("========================================\n");
+	abort();
+}
+
+
+int main(int argc, char *argv[])
+{
+	int ret;
+	struct fuse_args args = FUSE_ARGS_INIT(argc, argv);
+
+	erofs_init_configure();
+	fprintf(stderr, "%s %s\n", basename(argv[0]), cfg.c_version);
+
+	if (signal(SIGSEGV, signal_handle_sigsegv) == SIG_ERR) {
+		fprintf(stderr, "failed to initialize signals\n");
+		ret = -errno;
+		goto err;
+	}
+
+	/* parse options */
+	ret = fuse_opt_parse(&args, &fusecfg, option_spec, optional_opt_func);
+	if (ret)
+		goto err;
+
+	if (fusecfg.show_help || !fusecfg.mountpoint)
+		usage();
+	cfg.c_dbg_lvl = fusecfg.debug_lvl;
+
+	if (fusecfg.odebug && cfg.c_dbg_lvl < EROFS_DBG)
+		cfg.c_dbg_lvl = EROFS_DBG;
+
+	erofsfuse_dumpcfg();
+	ret = dev_open_ro(fusecfg.disk);
+	if (ret) {
+		fprintf(stderr, "failed to open: %s\n", fusecfg.disk);
+		goto err_fuse_free_args;
+	}
+
+	ret = erofs_read_superblock();
+	if (ret) {
+		fprintf(stderr, "failed to read erofs super block\n");
+		goto err_dev_close;
+	}
+
+	ret = fuse_main(args.argc, args.argv, &erofs_ops, NULL);
+err_dev_close:
+	dev_close();
+err_fuse_free_args:
+	fuse_opt_free_args(&args);
+err:
+	erofs_exit_configure();
+	return ret ? EXIT_FAILURE : EXIT_SUCCESS;
+}
+
diff --git a/include/erofs/internal.h b/include/erofs/internal.h
index cabb2faa0072..ec2646c23b78 100644
--- a/include/erofs/internal.h
+++ b/include/erofs/internal.h
@@ -36,6 +36,8 @@ typedef unsigned short umode_t;
 #error incompatible PAGE_SIZE is already defined
 #endif
 
+#define PAGE_MASK		(~(PAGE_SIZE-1))
+
 #define LOG_BLOCK_SIZE          (12)
 #define EROFS_BLKSIZ            (1U << LOG_BLOCK_SIZE)
 
@@ -59,6 +61,8 @@ typedef u32 erofs_blk_t;
 struct erofs_buffer_head;
 
 struct erofs_sb_info {
+	u64 blocks;
+
 	erofs_blk_t meta_blkaddr;
 	erofs_blk_t xattr_blkaddr;
 
@@ -66,12 +70,25 @@ struct erofs_sb_info {
 	u32 feature_incompat;
 	u64 build_time;
 	u32 build_time_nsec;
+
+	unsigned char islotbits;
+
+	/* what we really care is nid, rather than ino.. */
+	erofs_nid_t root_nid;
+	/* used for statfs, f_files - f_favail */
+	u64 inos;
+
 	u8 uuid[16];
 };
 
 /* global sbi */
 extern struct erofs_sb_info sbi;
 
+static inline erofs_off_t iloc(erofs_nid_t nid)
+{
+	return blknr_to_addr(sbi.meta_blkaddr) + (nid << sbi.islotbits);
+}
+
 #define EROFS_FEATURE_FUNCS(name, compat, feature) \
 static inline bool erofs_sb_has_##name(void) \
 { \
@@ -126,7 +143,16 @@ struct erofs_inode {
 	struct erofs_buffer_head *bh_inline, *bh_data;
 
 	void *idata;
-	void *compressmeta;
+
+	union {
+		void *compressmeta;
+		struct {
+			uint16_t z_advise;
+			uint8_t  z_algorithmtype[2];
+			uint8_t  z_logical_clusterbits;
+			uint8_t  z_physical_clusterbits[2];
+		};
+	};
 #ifdef WITH_ANDROID
 	uint64_t capabilities;
 #endif
@@ -137,6 +163,24 @@ static inline bool is_inode_layout_compression(struct erofs_inode *inode)
 	return erofs_inode_is_data_compressed(inode->datalayout);
 }
 
+static inline unsigned int erofs_bitrange(unsigned int value, unsigned int bit,
+					  unsigned int bits)
+{
+	return (value >> bit) & ((1 << bits) - 1);
+}
+
+static inline unsigned int erofs_inode_version(unsigned int value)
+{
+	return erofs_bitrange(value, EROFS_I_VERSION_BIT,
+			      EROFS_I_VERSION_BITS);
+}
+
+static inline unsigned int erofs_inode_datalayout(unsigned int value)
+{
+	return erofs_bitrange(value, EROFS_I_DATALAYOUT_BIT,
+			      EROFS_I_DATALAYOUT_BITS);
+}
+
 #define IS_ROOT(x)	((x) == (x)->i_parent)
 
 struct erofs_dentry {
@@ -169,5 +213,43 @@ static inline const char *erofs_strerror(int err)
 	return msg;
 }
 
+enum {
+	BH_Meta,
+	BH_Mapped,
+	BH_Zipped,
+	BH_FullMapped,
+};
+
+/* Has a disk mapping */
+#define EROFS_MAP_MAPPED	(1 << BH_Mapped)
+/* Located in metadata (could be copied from bd_inode) */
+#define EROFS_MAP_META		(1 << BH_Meta)
+/* The extent has been compressed */
+#define EROFS_MAP_ZIPPED	(1 << BH_Zipped)
+/* The length of extent is full */
+#define EROFS_MAP_FULL_MAPPED	(1 << BH_FullMapped)
+
+struct erofs_map_blocks {
+	char mpage[EROFS_BLKSIZ];
+
+	erofs_off_t m_pa, m_la;
+	u64 m_plen, m_llen;
+
+	unsigned int m_flags;
+	erofs_blk_t index;
+};
+
+/* super.c */
+int erofs_read_superblock(void);
+
+/* namei.c */
+int erofs_ilookup(const char *path, struct erofs_inode *vi);
+
+/* data.c */
+int erofs_pread(struct erofs_inode *inode, char *buf,
+		erofs_off_t count, erofs_off_t offset);
+
+#define EFSCORRUPTED	EUCLEAN		/* Filesystem is corrupted */
+
 #endif
 
diff --git a/include/erofs/io.h b/include/erofs/io.h
index a23de64541c6..557424578ece 100644
--- a/include/erofs/io.h
+++ b/include/erofs/io.h
@@ -17,6 +17,7 @@
 #endif
 
 int dev_open(const char *devname);
+int dev_open_ro(const char *dev);
 void dev_close(void);
 int dev_write(const void *buf, u64 offset, size_t len);
 int dev_read(void *buf, u64 offset, size_t len);
diff --git a/include/erofs/trace.h b/include/erofs/trace.h
new file mode 100644
index 000000000000..5a12da753d70
--- /dev/null
+++ b/include/erofs/trace.h
@@ -0,0 +1,14 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * erofs-utils/include/erofs/trace.h
+ *
+ * Copyright (C) 2020 Gao Xiang <hsiangkao@aol.com>
+ */
+#ifndef __EROFS_TRACE_H
+#define __EROFS_TRACE_H
+
+#define trace_erofs_map_blocks_flatmode_enter(inode, map, flags) ((void)0)
+#define trace_erofs_map_blocks_flatmode_exit(inode, map, flags, ret) ((void)0)
+
+#endif
+
diff --git a/include/erofs_fs.h b/include/erofs_fs.h
index 4cd79f01d820..a69f179a51a5 100644
--- a/include/erofs_fs.h
+++ b/include/erofs_fs.h
@@ -279,6 +279,10 @@ struct z_erofs_vle_decompressed_index {
 	} di_u;
 };
 
+#define Z_EROFS_VLE_LEGACY_INDEX_ALIGN(size) \
+	(round_up(size, sizeof(struct z_erofs_vle_decompressed_index)) + \
+	 sizeof(struct z_erofs_map_header) + Z_EROFS_VLE_LEGACY_HEADER_PADDING)
+
 #define Z_EROFS_VLE_EXTENT_ALIGN(size) round_up(size, \
 	sizeof(struct z_erofs_vle_decompressed_index))
 
diff --git a/lib/Makefile.am b/lib/Makefile.am
index e4b51e65f053..e1c43fa89009 100644
--- a/lib/Makefile.am
+++ b/lib/Makefile.am
@@ -2,8 +2,8 @@
 # Makefile.am
 
 noinst_LTLIBRARIES = liberofs.la
-liberofs_la_SOURCES = config.c io.c cache.c inode.c xattr.c \
-		      compress.c compressor.c exclude.c
+liberofs_la_SOURCES = config.c io.c cache.c super.c inode.c xattr.c exclude.c \
+		      namei.c data.c compress.c compressor.c
 liberofs_la_CFLAGS = -Wall -Werror -I$(top_srcdir)/include
 if ENABLE_LZ4
 liberofs_la_CFLAGS += ${LZ4_CFLAGS}
diff --git a/lib/data.c b/lib/data.c
new file mode 100644
index 000000000000..0337521f560e
--- /dev/null
+++ b/lib/data.c
@@ -0,0 +1,134 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * erofs-utils/lib/data.c
+ *
+ * Copyright (C) 2020 Gao Xiang <hsiangkao@aol.com>
+ * Compression support by Huang Jianan <huangjianan@oppo.com>
+ */
+#include "erofs/print.h"
+#include "erofs/internal.h"
+#include "erofs/io.h"
+#include "erofs/trace.h"
+
+static int erofs_map_blocks_flatmode(struct erofs_inode *inode,
+				     struct erofs_map_blocks *map,
+				     int flags)
+{
+	int err = 0;
+	erofs_blk_t nblocks, lastblk;
+	u64 offset = map->m_la;
+	struct erofs_inode *vi = inode;
+	bool tailendpacking = (vi->datalayout == EROFS_INODE_FLAT_INLINE);
+
+	trace_erofs_map_blocks_flatmode_enter(inode, map, flags);
+
+	nblocks = DIV_ROUND_UP(inode->i_size, PAGE_SIZE);
+	lastblk = nblocks - tailendpacking;
+
+	if (offset >= inode->i_size) {
+		/* leave out-of-bound access unmapped */
+		map->m_flags = 0;
+		goto out;
+	}
+
+	/* there is no hole in flatmode */
+	map->m_flags = EROFS_MAP_MAPPED;
+
+	if (offset < blknr_to_addr(lastblk)) {
+		map->m_pa = blknr_to_addr(vi->u.i_blkaddr) + map->m_la;
+		map->m_plen = blknr_to_addr(lastblk) - offset;
+	} else if (tailendpacking) {
+		/* 2 - inode inline B: inode, [xattrs], inline last blk... */
+		map->m_pa = iloc(vi->nid) + vi->inode_isize +
+			vi->xattr_isize + erofs_blkoff(map->m_la);
+		map->m_plen = inode->i_size - offset;
+
+		/* inline data should be located in one meta block */
+		if (erofs_blkoff(map->m_pa) + map->m_plen > PAGE_SIZE) {
+			erofs_err("inline data cross block boundary @ nid %" PRIu64,
+				  vi->nid);
+			DBG_BUGON(1);
+			err = -EFSCORRUPTED;
+			goto err_out;
+		}
+
+		map->m_flags |= EROFS_MAP_META;
+	} else {
+		erofs_err("internal error @ nid: %" PRIu64 " (size %llu), m_la 0x%" PRIx64,
+			  vi->nid, (unsigned long long)inode->i_size, map->m_la);
+		DBG_BUGON(1);
+		err = -EIO;
+		goto err_out;
+	}
+
+out:
+	map->m_llen = map->m_plen;
+
+err_out:
+	trace_erofs_map_blocks_flatmode_exit(inode, map, flags, 0);
+	return err;
+}
+
+static int erofs_read_raw_data(struct erofs_inode *inode, char *buffer,
+			       erofs_off_t size, erofs_off_t offset)
+{
+	struct erofs_map_blocks map = {
+		.index = UINT_MAX,
+	};
+	int ret;
+	erofs_off_t ptr = offset;
+
+	while (ptr < offset + size) {
+		erofs_off_t eend;
+
+		map.m_la = ptr;
+		ret = erofs_map_blocks_flatmode(inode, &map, 0);
+		if (ret)
+			return ret;
+
+		DBG_BUGON(map.m_plen != map.m_llen);
+
+		if (!(map.m_flags & EROFS_MAP_MAPPED)) {
+			if (!map.m_llen) {
+				ptr = offset + size;
+				continue;
+			}
+			ptr = map.m_la + map.m_llen;
+			continue;
+		}
+
+		/* trim extent */
+		eend = min(offset + size, map.m_la + map.m_llen);
+		DBG_BUGON(ptr < map.m_la);
+
+		if (ptr > map.m_la) {
+			map.m_pa += ptr - map.m_la;
+			map.m_la = ptr;
+		}
+
+		ret = dev_read(buffer + ptr - offset,
+			       map.m_pa, eend - map.m_la);
+		if (ret < 0)
+			return -EIO;
+
+		ptr = eend;
+	}
+	return 0;
+}
+
+int erofs_pread(struct erofs_inode *inode, char *buf,
+		erofs_off_t count, erofs_off_t offset)
+{
+	switch (inode->datalayout) {
+	case EROFS_INODE_FLAT_PLAIN:
+	case EROFS_INODE_FLAT_INLINE:
+		return erofs_read_raw_data(inode, buf, count, offset);
+	case EROFS_INODE_FLAT_COMPRESSION_LEGACY:
+	case EROFS_INODE_FLAT_COMPRESSION:
+		return -EOPNOTSUPP;
+	default:
+		break;
+	}
+	return -EINVAL;
+}
+
diff --git a/lib/io.c b/lib/io.c
index 4f5d9a6edaa4..d835f34da50f 100644
--- a/lib/io.c
+++ b/lib/io.c
@@ -108,6 +108,22 @@ int dev_open(const char *dev)
 	return 0;
 }
 
+/* XXX: temporary soluation. Disk I/O implementation needs to be refactored. */
+int dev_open_ro(const char *dev)
+{
+	int fd = open(dev, O_RDONLY | O_BINARY);
+
+	if (fd < 0) {
+		erofs_err("failed to open(%s).", dev);
+		return -errno;
+	}
+
+	erofs_devfd = fd;
+	erofs_devname = dev;
+	erofs_devsz = INT64_MAX;
+	return 0;
+}
+
 u64 dev_length(void)
 {
 	return erofs_devsz;
diff --git a/lib/namei.c b/lib/namei.c
new file mode 100644
index 000000000000..b05f5c421d54
--- /dev/null
+++ b/lib/namei.c
@@ -0,0 +1,246 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * erofs-utils/lib/namei.c
+ *
+ * Created by Li Guifu <blucerlee@gmail.com>
+ */
+#include <linux/kdev_t.h>
+#include <sys/types.h>
+#include <unistd.h>
+#include <stdio.h>
+#include <errno.h>
+#include <sys/stat.h>
+#include <sys/sysmacros.h>
+
+#include "erofs/print.h"
+#include "erofs/io.h"
+
+static int erofs_read_inode_from_disk(struct erofs_inode *vi)
+{
+	int ret, ifmt;
+	char buf[sizeof(struct erofs_inode_extended)];
+	struct erofs_inode_compact *dic;
+	struct erofs_inode_extended *die;
+	const erofs_off_t inode_loc = iloc(vi->nid);
+
+	ret = dev_read(buf, inode_loc, sizeof(*dic));
+	if (ret < 0)
+		return -EIO;
+
+	dic = (struct erofs_inode_compact *)buf;
+	ifmt = le16_to_cpu(dic->i_format);
+
+	vi->datalayout = erofs_inode_datalayout(ifmt);
+	if (vi->datalayout >= EROFS_INODE_DATALAYOUT_MAX) {
+		erofs_err("unsupported datalayout %u of nid %llu",
+			  vi->datalayout, vi->nid | 0ULL);
+		return -EOPNOTSUPP;
+	}
+	switch (erofs_inode_version(ifmt)) {
+	case EROFS_INODE_LAYOUT_EXTENDED:
+		vi->inode_isize = sizeof(struct erofs_inode_extended);
+
+		ret = dev_read(buf + sizeof(*dic), inode_loc + sizeof(*dic),
+			       sizeof(*die) - sizeof(*dic));
+		if (ret < 0)
+			return -EIO;
+
+		die = (struct erofs_inode_extended *)buf;
+		vi->xattr_isize = erofs_xattr_ibody_size(die->i_xattr_icount);
+		vi->i_mode = le16_to_cpu(die->i_mode);
+
+		switch (vi->i_mode & S_IFMT) {
+		case S_IFREG:
+		case S_IFDIR:
+		case S_IFLNK:
+			vi->u.i_blkaddr = le32_to_cpu(die->i_u.raw_blkaddr);
+			break;
+		case S_IFCHR:
+		case S_IFBLK:
+			return -EOPNOTSUPP;
+		case S_IFIFO:
+		case S_IFSOCK:
+			return -EOPNOTSUPP;
+		default:
+			goto bogusimode;
+		}
+
+		vi->i_uid = le32_to_cpu(die->i_uid);
+		vi->i_gid = le32_to_cpu(die->i_gid);
+		vi->i_nlink = le32_to_cpu(die->i_nlink);
+
+		vi->i_ctime = le64_to_cpu(die->i_ctime);
+		vi->i_ctime_nsec = le64_to_cpu(die->i_ctime_nsec);
+		vi->i_size = le64_to_cpu(die->i_size);
+		break;
+	case EROFS_INODE_LAYOUT_COMPACT:
+		vi->inode_isize = sizeof(struct erofs_inode_compact);
+		vi->xattr_isize = erofs_xattr_ibody_size(dic->i_xattr_icount);
+		vi->i_mode = le16_to_cpu(dic->i_mode);
+
+		switch (vi->i_mode & S_IFMT) {
+		case S_IFREG:
+		case S_IFDIR:
+		case S_IFLNK:
+			vi->u.i_blkaddr = le32_to_cpu(dic->i_u.raw_blkaddr);
+			break;
+		case S_IFCHR:
+		case S_IFBLK:
+			return -EOPNOTSUPP;
+		case S_IFIFO:
+		case S_IFSOCK:
+			return -EOPNOTSUPP;
+		default:
+			goto bogusimode;
+		}
+
+		vi->i_uid = le16_to_cpu(dic->i_uid);
+		vi->i_gid = le16_to_cpu(dic->i_gid);
+		vi->i_nlink = le16_to_cpu(dic->i_nlink);
+
+		vi->i_ctime = sbi.build_time;
+		vi->i_ctime_nsec = sbi.build_time_nsec;
+
+		vi->i_size = le32_to_cpu(dic->i_size);
+		break;
+	default:
+		erofs_err("unsupported on-disk inode version %u of nid %llu",
+			  erofs_inode_version(ifmt), vi->nid | 0ULL);
+		return -EOPNOTSUPP;
+	}
+	return 0;
+bogusimode:
+	erofs_err("bogus i_mode (%o) @ nid %llu", vi->i_mode, vi->nid | 0ULL);
+	return -EFSCORRUPTED;
+}
+
+
+struct erofs_dirent *find_target_dirent(erofs_nid_t pnid,
+					void *dentry_blk,
+					const char *name, unsigned int len,
+					unsigned int nameoff,
+					unsigned int maxsize)
+{
+	struct erofs_dirent *de = dentry_blk;
+	const struct erofs_dirent *end = dentry_blk + nameoff;
+
+	while (de < end) {
+		const char *de_name;
+		unsigned int de_namelen;
+
+		nameoff = le16_to_cpu(de->nameoff);
+		de_name = (char *)dentry_blk + nameoff;
+
+		/* the last dirent in the block? */
+		if (de + 1 >= end)
+			de_namelen = strnlen(de_name, maxsize - nameoff);
+		else
+			de_namelen = le16_to_cpu(de[1].nameoff) - nameoff;
+
+		/* a corrupted entry is found */
+		if (nameoff + de_namelen > maxsize ||
+		    de_namelen > EROFS_NAME_LEN) {
+			erofs_err("bogus dirent @ nid %llu", pnid | 0ULL);
+			DBG_BUGON(1);
+			return ERR_PTR(-EFSCORRUPTED);
+		}
+
+		if (len == de_namelen && !memcmp(de_name, name, de_namelen))
+			return de;
+		++de;
+	}
+	return NULL;
+}
+
+struct nameidata {
+	erofs_nid_t	nid;
+	unsigned int	ftype;
+};
+
+int erofs_namei(struct nameidata *nd,
+		const char *name, unsigned int len)
+{
+	erofs_nid_t nid = nd->nid;
+	int ret;
+	char buf[EROFS_BLKSIZ];
+	struct erofs_inode vi = { .nid = nid };
+	erofs_off_t offset;
+
+	ret = erofs_read_inode_from_disk(&vi);
+	if (ret)
+		return ret;
+
+	offset = 0;
+	while (offset < vi.i_size) {
+		erofs_off_t maxsize = min_t(erofs_off_t,
+					    vi.i_size - offset, EROFS_BLKSIZ);
+		struct erofs_dirent *de = (void *)buf;
+		unsigned int nameoff;
+
+		ret = erofs_pread(&vi, buf, maxsize, offset);
+		if (ret)
+			return ret;
+
+		nameoff = le16_to_cpu(de->nameoff);
+		if (nameoff < sizeof(struct erofs_dirent) ||
+		    nameoff >= PAGE_SIZE) {
+			erofs_err("invalid de[0].nameoff %u @ nid %llu",
+				  nameoff, nid | 0ULL);
+			return -EFSCORRUPTED;
+		}
+
+		de = find_target_dirent(nid, buf, name, len,
+					nameoff, maxsize);
+		if (IS_ERR(de))
+			return PTR_ERR(de);
+
+		if (de) {
+			nd->nid = le64_to_cpu(de->nid);
+			return 0;
+		}
+		offset += maxsize;
+	}
+	return -ENOENT;
+}
+
+static int link_path_walk(const char *name, struct nameidata *nd)
+{
+	nd->nid = sbi.root_nid;
+
+	while (*name == '/')
+		name++;
+
+	/* At this point we know we have a real path component. */
+	while (*name != '\0') {
+		const char *p = name;
+		int ret;
+
+		do {
+			++p;
+		} while (*p != '\0' && *p != '/');
+
+		DBG_BUGON(p <= name);
+		ret = erofs_namei(nd, name, p - name);
+		if (ret)
+			return ret;
+
+		name = p;
+		/* Skip until no more slashes. */
+		for (name = p; *name == '/'; ++name);
+	}
+	return 0;
+}
+
+int erofs_ilookup(const char *path, struct erofs_inode *vi)
+{
+	int ret;
+	struct nameidata nd;
+
+	ret = link_path_walk(path, &nd);
+	if (ret)
+		return ret;
+
+	vi->nid = nd.nid;
+	return erofs_read_inode_from_disk(vi);
+}
+
diff --git a/lib/super.c b/lib/super.c
new file mode 100644
index 000000000000..2d366928e12b
--- /dev/null
+++ b/lib/super.c
@@ -0,0 +1,78 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * erofs-utils/lib/super.c
+ *
+ * Created by Li Guifu <blucerlee@gmail.com>
+ */
+#include <string.h>
+#include <stdlib.h>
+#include <asm-generic/errno-base.h>
+
+#include "erofs/io.h"
+#include "erofs/print.h"
+
+struct erofs_sb_info sbi;
+
+static bool check_layout_compatibility(struct erofs_sb_info *sbi,
+				       struct erofs_super_block *dsb)
+{
+	const unsigned int feature = le32_to_cpu(dsb->feature_incompat);
+
+	sbi->feature_incompat = feature;
+
+	/* check if current kernel meets all mandatory requirements */
+	if (feature & (~EROFS_ALL_FEATURE_INCOMPAT)) {
+		erofs_err("unidentified incompatible feature %x, please upgrade kernel version",
+			  feature & ~EROFS_ALL_FEATURE_INCOMPAT);
+		return false;
+	}
+	return true;
+}
+
+int erofs_read_superblock(void)
+{
+	char data[EROFS_BLKSIZ];
+	struct erofs_super_block *dsb;
+	unsigned int blkszbits;
+	int ret;
+
+	ret = blk_read(data, 0, 1);
+	if (ret < 0) {
+		erofs_err("cannot read erofs superblock: %d", ret);
+		return -EIO;
+	}
+	dsb = (struct erofs_super_block *)(data + EROFS_SUPER_OFFSET);
+
+	ret = -EINVAL;
+	if (le32_to_cpu(dsb->magic) != EROFS_SUPER_MAGIC_V1) {
+		erofs_err("cannot find valid erofs superblock");
+		return ret;
+	}
+
+	sbi.feature_compat = le32_to_cpu(dsb->feature_compat);
+
+	blkszbits = dsb->blkszbits;
+	/* 9(512 bytes) + LOG_SECTORS_PER_BLOCK == LOG_BLOCK_SIZE */
+	if (blkszbits != LOG_BLOCK_SIZE) {
+		erofs_err("blksize %u isn't supported on this platform",
+			  1 << blkszbits);
+		return ret;
+	}
+
+	if (!check_layout_compatibility(&sbi, dsb))
+		return ret;
+
+	sbi.blocks = le32_to_cpu(dsb->blocks);
+	sbi.meta_blkaddr = le32_to_cpu(dsb->meta_blkaddr);
+	sbi.xattr_blkaddr = le32_to_cpu(dsb->xattr_blkaddr);
+	sbi.islotbits = EROFS_ISLOTBITS;
+	sbi.root_nid = le16_to_cpu(dsb->root_nid);
+	sbi.inos = le64_to_cpu(dsb->inos);
+
+	sbi.build_time = le64_to_cpu(dsb->build_time);
+	sbi.build_time_nsec = le32_to_cpu(dsb->build_time_nsec);
+
+	memcpy(&sbi.uuid, dsb->uuid, sizeof(dsb->uuid));
+	return 0;
+}
+
-- 
2.24.0

[PATCH v3 2/3] erofs-utils: fuse: support symlink & special inode

[Gao Xiang via Linux-erofs]

From: Huang Jianan <huangjianan@oppo.com>

This patch adds symlink and special inode (e.g. block dev, char,
socket, pipe inode) support.

Signed-off-by: Huang Jianan <huangjianan@oppo.com>
Signed-off-by: Guo Weichao <guoweichao@oppo.com>
Signed-off-by: Gao Xiang <hsiangkao@aol.com>
---
 fuse/main.c | 10 ++++++++++
 lib/namei.c | 22 ++++++++++++++++++----
 2 files changed, 28 insertions(+), 4 deletions(-)

diff --git a/fuse/main.c b/fuse/main.c
index ab8a90aadf8a..1e24efe110c2 100644
--- a/fuse/main.c
+++ b/fuse/main.c
@@ -78,7 +78,17 @@ static int erofsfuse_read(const char *path, char *buffer,
 	return size;
 }
 
+static int erofsfuse_readlink(const char *path, char *buffer, size_t size)
+{
+	int ret = erofsfuse_read(path, buffer, size, 0, NULL);
+
+	if (ret < 0)
+		return ret;
+	return 0;
+}
+
 static struct fuse_operations erofs_ops = {
+	.readlink = erofsfuse_readlink,
 	.getattr = erofsfuse_getattr,
 	.readdir = erofsfuse_readdir,
 	.open = erofsfuse_open,
diff --git a/lib/namei.c b/lib/namei.c
index b05f5c421d54..e8275a42f090 100644
--- a/lib/namei.c
+++ b/lib/namei.c
@@ -15,6 +15,14 @@
 #include "erofs/print.h"
 #include "erofs/io.h"
 
+static dev_t erofs_new_decode_dev(u32 dev)
+{
+	const unsigned int major = (dev & 0xfff00) >> 8;
+	const unsigned int minor = (dev & 0xff) | ((dev >> 12) & 0xfff00);
+
+	return makedev(major, minor);
+}
+
 static int erofs_read_inode_from_disk(struct erofs_inode *vi)
 {
 	int ret, ifmt;
@@ -57,10 +65,13 @@ static int erofs_read_inode_from_disk(struct erofs_inode *vi)
 			break;
 		case S_IFCHR:
 		case S_IFBLK:
-			return -EOPNOTSUPP;
+			vi->u.i_rdev =
+				erofs_new_decode_dev(le32_to_cpu(die->i_u.rdev));
+			break;
 		case S_IFIFO:
 		case S_IFSOCK:
-			return -EOPNOTSUPP;
+			vi->u.i_rdev = 0;
+			break;
 		default:
 			goto bogusimode;
 		}
@@ -86,10 +97,13 @@ static int erofs_read_inode_from_disk(struct erofs_inode *vi)
 			break;
 		case S_IFCHR:
 		case S_IFBLK:
-			return -EOPNOTSUPP;
+			vi->u.i_rdev =
+				erofs_new_decode_dev(le32_to_cpu(dic->i_u.rdev));
+			break;
 		case S_IFIFO:
 		case S_IFSOCK:
-			return -EOPNOTSUPP;
+			vi->u.i_rdev = 0;
+			break;
 		default:
 			goto bogusimode;
 		}
-- 
2.24.0

Re: [PATCH v3 2/3] erofs-utils: fuse: support symlink & special inode

[Li GuiFu via Linux-erofs]

On 2020/11/27 19:46, Gao Xiang via Linux-erofs wrote:
> From: Huang Jianan <huangjianan@oppo.com>
> 
> This patch adds symlink and special inode (e.g. block dev, char,
> socket, pipe inode) support.
> 
> Signed-off-by: Huang Jianan <huangjianan@oppo.com>
> Signed-off-by: Guo Weichao <guoweichao@oppo.com>
> Signed-off-by: Gao Xiang <hsiangkao@aol.com>
> ---
>  fuse/main.c | 10 ++++++++++
>  lib/namei.c | 22 ++++++++++++++++++----
>  2 files changed, 28 insertions(+), 4 deletions(-)
> 

It looks good
Reviewed-by: Li Guifu <bluce.lee@aliyun.com>
Tested-by: Li Guifu <bluce.lee@aliyun.com>
Thanks,

Re: [PATCH v3 2/3] erofs-utils: fuse: support symlink & special inode

[Gao Xiang]

Hi Guifu,

On Sat, Dec 05, 2020 at 04:42:04PM +0800, Li GuiFu via Linux-erofs wrote:
> 
> 
> On 2020/11/27 19:46, Gao Xiang via Linux-erofs wrote:
> > From: Huang Jianan <huangjianan@oppo.com>
> > 
> > This patch adds symlink and special inode (e.g. block dev, char,
> > socket, pipe inode) support.
> > 
> > Signed-off-by: Huang Jianan <huangjianan@oppo.com>
> > Signed-off-by: Guo Weichao <guoweichao@oppo.com>
> > Signed-off-by: Gao Xiang <hsiangkao@aol.com>
> > ---
> >  fuse/main.c | 10 ++++++++++
> >  lib/namei.c | 22 ++++++++++++++++++----
> >  2 files changed, 28 insertions(+), 4 deletions(-)
> > 
> 
> It looks good
> Reviewed-by: Li Guifu <bluce.lee@aliyun.com>
> Tested-by: Li Guifu <bluce.lee@aliyun.com>

My tendency is that once a patch is merged to dev branch from
experimental. There is no chance to apply more tags since we need to
stablize the commit ID for dev/master branch (git commit --amend will
modify the original commit ID). So I have to ignore these RVB tags
for the reason above.

And the merging route is "experimental" (can rebase) -> "dev" (cannot
rebase) -> "master".

Also, it's actually hard to carefully review erofsfuse code here with
limited time if your bandwidth is limited as well, so I applied directly
as what I said in
https://lore.kernel.org/r/20201127131630.GA654423@xiangao.remote.csb/

But yeah, more testing is always welcome, and thanks for the testing :)

Finally, my suggestion is that it's better to use erofsfuse rather than
customized ".ko" for older linux x86 versions at HUAWEI as well, since
the old internal ".ko" versions are quite hacky and messy (at least due
to many kernel API changes).

Thanks,
Gao Xiang

[PATCH v3 3/3] erofs-utils: fuse: add compressed file support

[Gao Xiang via Linux-erofs]

From: Huang Jianan <huangjianan@oppo.com>

This patch adds a simple approach (~ 700 LOC) to EROFS fixed-sized
output decompression without inplace I/O or decompression inplace
so it's easy to be ported everywhere with less constraint.

However, the on-disk compressed index parser (aka. zmap) is largely
kept in line with the kernel side, therefore new on-disk features
under development can be verified effectively first here.

Signed-off-by: Huang Jianan <huangjianan@oppo.com>
Signed-off-by: Guo Weichao <guoweichao@oppo.com>
Signed-off-by: Gao Xiang <hsiangkao@aol.com>
---
 include/erofs/decompress.h |  35 ++++
 include/erofs/defs.h       |   5 +
 include/erofs/internal.h   |   8 +
 lib/Makefile.am            |   2 +-
 lib/data.c                 |  72 ++++++-
 lib/decompress.c           |  87 ++++++++
 lib/namei.c                |   4 +
 lib/zmap.c                 | 415 +++++++++++++++++++++++++++++++++++++
 8 files changed, 626 insertions(+), 2 deletions(-)
 create mode 100644 include/erofs/decompress.h
 create mode 100644 lib/decompress.c
 create mode 100644 lib/zmap.c

diff --git a/include/erofs/decompress.h b/include/erofs/decompress.h
new file mode 100644
index 000000000000..beaac359b21f
--- /dev/null
+++ b/include/erofs/decompress.h
@@ -0,0 +1,35 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * erofs-utils/include/erofs/decompress.h
+ *
+ * Copyright (C), 2008-2020, OPPO Mobile Comm Corp., Ltd.
+ * Created by Huang Jianan <huangjianan@oppo.com>
+ */
+#ifndef __EROFS_DECOMPRESS_H
+#define __EROFS_DECOMPRESS_H
+
+#include "internal.h"
+
+enum {
+	Z_EROFS_COMPRESSION_SHIFTED = Z_EROFS_COMPRESSION_MAX,
+	Z_EROFS_COMPRESSION_RUNTIME_MAX
+};
+
+struct z_erofs_decompress_req {
+	char *in, *out;
+
+	/*
+	 * initial decompressed bytes that need to be skipped
+	 * when finally copying to output buffer
+	 */
+	unsigned int decodedskip;
+	unsigned int inputsize, decodedlength;
+
+	/* indicate the algorithm will be used for decompression */
+	unsigned int alg;
+	bool partial_decoding;
+};
+
+int z_erofs_decompress(struct z_erofs_decompress_req *rq);
+
+#endif
diff --git a/include/erofs/defs.h b/include/erofs/defs.h
index 8dee661ab9f0..b54cd9d99981 100644
--- a/include/erofs/defs.h
+++ b/include/erofs/defs.h
@@ -170,5 +170,10 @@ typedef int64_t         s64;
 #define __maybe_unused      __attribute__((__unused__))
 #endif
 
+static inline u32 get_unaligned_le32(const u8 *p)
+{
+	return p[0] | p[1] << 8 | p[2] << 16 | p[3] << 24;
+}
+
 #endif
 
diff --git a/include/erofs/internal.h b/include/erofs/internal.h
index ec2646c23b78..bf13c166ba16 100644
--- a/include/erofs/internal.h
+++ b/include/erofs/internal.h
@@ -106,9 +106,13 @@ static inline void erofs_sb_clear_##name(void) \
 EROFS_FEATURE_FUNCS(lz4_0padding, incompat, INCOMPAT_LZ4_0PADDING)
 EROFS_FEATURE_FUNCS(sb_chksum, compat, COMPAT_SB_CHKSUM)
 
+#define EROFS_I_EA_INITED	(1 << 0)
+#define EROFS_I_Z_INITED	(1 << 1)
+
 struct erofs_inode {
 	struct list_head i_hash, i_subdirs, i_xattrs;
 
+	unsigned int flags;
 	unsigned int i_count;
 	struct erofs_inode *i_parent;
 
@@ -248,6 +252,10 @@ int erofs_ilookup(const char *path, struct erofs_inode *vi);
 /* data.c */
 int erofs_pread(struct erofs_inode *inode, char *buf,
 		erofs_off_t count, erofs_off_t offset);
+/* zmap.c */
+int z_erofs_fill_inode(struct erofs_inode *vi);
+int z_erofs_map_blocks_iter(struct erofs_inode *vi,
+			    struct erofs_map_blocks *map);
 
 #define EFSCORRUPTED	EUCLEAN		/* Filesystem is corrupted */
 
diff --git a/lib/Makefile.am b/lib/Makefile.am
index e1c43fa89009..f21dc35eda51 100644
--- a/lib/Makefile.am
+++ b/lib/Makefile.am
@@ -3,7 +3,7 @@
 
 noinst_LTLIBRARIES = liberofs.la
 liberofs_la_SOURCES = config.c io.c cache.c super.c inode.c xattr.c exclude.c \
-		      namei.c data.c compress.c compressor.c
+		      namei.c data.c compress.c compressor.c zmap.c decompress.c
 liberofs_la_CFLAGS = -Wall -Werror -I$(top_srcdir)/include
 if ENABLE_LZ4
 liberofs_la_CFLAGS += ${LZ4_CFLAGS}
diff --git a/lib/data.c b/lib/data.c
index 0337521f560e..3781846743aa 100644
--- a/lib/data.c
+++ b/lib/data.c
@@ -9,6 +9,7 @@
 #include "erofs/internal.h"
 #include "erofs/io.h"
 #include "erofs/trace.h"
+#include "erofs/decompress.h"
 
 static int erofs_map_blocks_flatmode(struct erofs_inode *inode,
 				     struct erofs_map_blocks *map,
@@ -116,6 +117,75 @@ static int erofs_read_raw_data(struct erofs_inode *inode, char *buffer,
 	return 0;
 }
 
+static int z_erofs_read_data(struct erofs_inode *inode, char *buffer,
+			     erofs_off_t size, erofs_off_t offset)
+{
+	int ret;
+	erofs_off_t end, length, skip;
+	struct erofs_map_blocks map = {
+		.index = UINT_MAX,
+	};
+	bool partial;
+	unsigned int algorithmformat;
+	char raw[EROFS_BLKSIZ];
+
+	end = offset + size;
+	while (end > offset) {
+		map.m_la = end - 1;
+
+		ret = z_erofs_map_blocks_iter(inode, &map);
+		if (ret)
+			return ret;
+
+		if (!(map.m_flags & EROFS_MAP_MAPPED)) {
+			end = map.m_la;
+			continue;
+		}
+
+		ret = dev_read(raw, map.m_pa, EROFS_BLKSIZ);
+		if (ret < 0)
+			return -EIO;
+
+		algorithmformat = map.m_flags & EROFS_MAP_ZIPPED ?
+						Z_EROFS_COMPRESSION_LZ4 :
+						Z_EROFS_COMPRESSION_SHIFTED;
+
+		/*
+		 * trim to the needed size if the returned extent is quite
+		 * larger than requested, and set up partial flag as well.
+		 */
+		if (end < map.m_la + map.m_llen) {
+			length = end - map.m_la;
+			partial = true;
+		} else {
+			DBG_BUGON(end != map.m_la + map.m_llen);
+			length = map.m_llen;
+			partial = !(map.m_flags & EROFS_MAP_FULL_MAPPED);
+		}
+
+		if (map.m_la < offset) {
+			skip = offset - map.m_la;
+			end = offset;
+		} else {
+			skip = 0;
+			end = map.m_la;
+		}
+
+		ret = z_erofs_decompress(&(struct z_erofs_decompress_req) {
+					.in = raw,
+					.out = buffer + end - offset,
+					.decodedskip = skip,
+					.inputsize = map.m_plen,
+					.decodedlength = length,
+					.alg = algorithmformat,
+					.partial_decoding = partial
+					 });
+		if (ret < 0)
+			return ret;
+	}
+	return 0;
+}
+
 int erofs_pread(struct erofs_inode *inode, char *buf,
 		erofs_off_t count, erofs_off_t offset)
 {
@@ -125,7 +195,7 @@ int erofs_pread(struct erofs_inode *inode, char *buf,
 		return erofs_read_raw_data(inode, buf, count, offset);
 	case EROFS_INODE_FLAT_COMPRESSION_LEGACY:
 	case EROFS_INODE_FLAT_COMPRESSION:
-		return -EOPNOTSUPP;
+		return z_erofs_read_data(inode, buf, count, offset);
 	default:
 		break;
 	}
diff --git a/lib/decompress.c b/lib/decompress.c
new file mode 100644
index 000000000000..870b85430dd1
--- /dev/null
+++ b/lib/decompress.c
@@ -0,0 +1,87 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * erofs-utils/lib/decompress.c
+ *
+ * Copyright (C), 2008-2020, OPPO Mobile Comm Corp., Ltd.
+ * Created by Huang Jianan <huangjianan@oppo.com>
+ */
+#include <stdlib.h>
+#include <lz4.h>
+
+#include "erofs/decompress.h"
+#include "erofs/err.h"
+
+#ifdef LZ4_ENABLED
+static int z_erofs_decompress_lz4(struct z_erofs_decompress_req *rq)
+{
+	int ret = 0;
+	char *dest = rq->out;
+	char *src = rq->in;
+	char *buff = NULL;
+	bool support_0padding = false;
+	unsigned int inputmargin = 0;
+
+	if (erofs_sb_has_lz4_0padding()) {
+		support_0padding = true;
+
+		while (!src[inputmargin & ~PAGE_MASK])
+			if (!(++inputmargin & ~PAGE_MASK))
+				break;
+
+		if (inputmargin >= rq->inputsize)
+			return -EIO;
+	}
+
+	if (rq->decodedskip) {
+		buff = malloc(rq->decodedlength);
+		if (!buff)
+			return -ENOMEM;
+		dest = buff;
+	}
+
+	if (rq->partial_decoding || !support_0padding)
+		ret = LZ4_decompress_safe_partial(src + inputmargin, dest,
+				rq->inputsize - inputmargin,
+				rq->decodedlength, rq->decodedlength);
+	else
+		ret = LZ4_decompress_safe(src + inputmargin, dest,
+					  rq->inputsize - inputmargin,
+					  rq->decodedlength);
+
+	if (ret != (int)rq->decodedlength) {
+		ret = -EIO;
+		goto out;
+	}
+
+	if (rq->decodedskip)
+		memcpy(rq->out, dest + rq->decodedskip,
+		       rq->decodedlength - rq->decodedskip);
+
+out:
+	if (buff)
+		free(buff);
+
+	return ret;
+}
+#endif
+
+int z_erofs_decompress(struct z_erofs_decompress_req *rq)
+{
+	if (rq->alg == Z_EROFS_COMPRESSION_SHIFTED) {
+		if (rq->inputsize != EROFS_BLKSIZ)
+			return -EFSCORRUPTED;
+
+		DBG_BUGON(rq->decodedlength > EROFS_BLKSIZ);
+		DBG_BUGON(rq->decodedlength < rq->decodedskip);
+
+		memcpy(rq->out, rq->in + rq->decodedskip,
+		       rq->decodedlength - rq->decodedskip);
+		return 0;
+	}
+
+#ifdef LZ4_ENABLED
+	if (rq->alg == Z_EROFS_COMPRESSION_LZ4)
+		return z_erofs_decompress_lz4(rq);
+#endif
+	return -EOPNOTSUPP;
+}
diff --git a/lib/namei.c b/lib/namei.c
index e8275a42f090..4e06ba468dc4 100644
--- a/lib/namei.c
+++ b/lib/namei.c
@@ -122,6 +122,10 @@ static int erofs_read_inode_from_disk(struct erofs_inode *vi)
 			  erofs_inode_version(ifmt), vi->nid | 0ULL);
 		return -EOPNOTSUPP;
 	}
+
+	vi->flags = 0;
+	if (erofs_inode_is_data_compressed(vi->datalayout))
+		z_erofs_fill_inode(vi);
 	return 0;
 bogusimode:
 	erofs_err("bogus i_mode (%o) @ nid %llu", vi->i_mode, vi->nid | 0ULL);
diff --git a/lib/zmap.c b/lib/zmap.c
new file mode 100644
index 000000000000..ee63de74cab2
--- /dev/null
+++ b/lib/zmap.c
@@ -0,0 +1,415 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * erofs-utils/lib/zmap.c
+ *
+ * (a large amount of code was adapted from Linux kernel. )
+ *
+ * Copyright (C) 2018-2019 HUAWEI, Inc.
+ *             https://www.huawei.com/
+ * Created by Gao Xiang <gaoxiang25@huawei.com>
+ * Modified by Huang Jianan <huangjianan@oppo.com>
+ */
+#include "erofs/io.h"
+#include "erofs/print.h"
+
+int z_erofs_fill_inode(struct erofs_inode *vi)
+{
+	if (vi->datalayout == EROFS_INODE_FLAT_COMPRESSION_LEGACY) {
+		vi->z_advise = 0;
+		vi->z_algorithmtype[0] = 0;
+		vi->z_algorithmtype[1] = 0;
+		vi->z_logical_clusterbits = LOG_BLOCK_SIZE;
+		vi->z_physical_clusterbits[0] = vi->z_logical_clusterbits;
+		vi->z_physical_clusterbits[1] = vi->z_logical_clusterbits;
+
+		vi->flags |= EROFS_I_Z_INITED;
+	}
+	return 0;
+}
+
+static int z_erofs_fill_inode_lazy(struct erofs_inode *vi)
+{
+	int ret;
+	erofs_off_t pos;
+	struct z_erofs_map_header *h;
+	char buf[sizeof(struct z_erofs_map_header)];
+
+	if (vi->flags & EROFS_I_Z_INITED)
+		return 0;
+
+	DBG_BUGON(vi->datalayout == EROFS_INODE_FLAT_COMPRESSION_LEGACY);
+	pos = round_up(iloc(vi->nid) + vi->inode_isize + vi->xattr_isize, 8);
+
+	ret = dev_read(buf, pos, sizeof(buf));
+	if (ret < 0)
+		return -EIO;
+
+	h = (struct z_erofs_map_header *)buf;
+	vi->z_advise = le16_to_cpu(h->h_advise);
+	vi->z_algorithmtype[0] = h->h_algorithmtype & 15;
+	vi->z_algorithmtype[1] = h->h_algorithmtype >> 4;
+
+	if (vi->z_algorithmtype[0] >= Z_EROFS_COMPRESSION_MAX) {
+		erofs_err("unknown compression format %u for nid %llu",
+			  vi->z_algorithmtype[0], (unsigned long long)vi->nid);
+		return -EOPNOTSUPP;
+	}
+
+	vi->z_logical_clusterbits = LOG_BLOCK_SIZE + (h->h_clusterbits & 7);
+	vi->z_physical_clusterbits[0] = vi->z_logical_clusterbits +
+					((h->h_clusterbits >> 3) & 3);
+
+	if (vi->z_physical_clusterbits[0] != LOG_BLOCK_SIZE) {
+		erofs_err("unsupported physical clusterbits %u for nid %llu",
+			  vi->z_physical_clusterbits[0], (unsigned long long)vi->nid);
+		return -EOPNOTSUPP;
+	}
+
+	vi->z_physical_clusterbits[1] = vi->z_logical_clusterbits +
+					((h->h_clusterbits >> 5) & 7);
+	vi->flags |= EROFS_I_Z_INITED;
+	return 0;
+}
+
+struct z_erofs_maprecorder {
+	struct erofs_inode *inode;
+	struct erofs_map_blocks *map;
+	void *kaddr;
+
+	unsigned long lcn;
+	/* compression extent information gathered */
+	u8  type;
+	u16 clusterofs;
+	u16 delta[2];
+	erofs_blk_t pblk;
+};
+
+static int z_erofs_reload_indexes(struct z_erofs_maprecorder *m,
+				  erofs_blk_t eblk)
+{
+	int ret;
+	struct erofs_map_blocks *const map = m->map;
+	char *mpage = map->mpage;
+
+	if (map->index == eblk)
+		return 0;
+
+	ret = blk_read(mpage, eblk, 1);
+	if (ret < 0)
+		return -EIO;
+
+	map->index = eblk;
+
+	return 0;
+}
+
+static int legacy_load_cluster_from_disk(struct z_erofs_maprecorder *m,
+					 unsigned long lcn)
+{
+	struct erofs_inode *const vi = m->inode;
+	const erofs_off_t ibase = iloc(vi->nid);
+	const erofs_off_t pos =
+		Z_EROFS_VLE_LEGACY_INDEX_ALIGN(ibase + vi->inode_isize +
+					       vi->xattr_isize) +
+		lcn * sizeof(struct z_erofs_vle_decompressed_index);
+	struct z_erofs_vle_decompressed_index *di;
+	unsigned int advise, type;
+	int err;
+
+	err = z_erofs_reload_indexes(m, erofs_blknr(pos));
+	if (err)
+		return err;
+
+	m->lcn = lcn;
+	di = m->kaddr + erofs_blkoff(pos);
+
+	advise = le16_to_cpu(di->di_advise);
+	type = (advise >> Z_EROFS_VLE_DI_CLUSTER_TYPE_BIT) &
+		((1 << Z_EROFS_VLE_DI_CLUSTER_TYPE_BITS) - 1);
+	switch (type) {
+	case Z_EROFS_VLE_CLUSTER_TYPE_NONHEAD:
+		m->clusterofs = 1 << vi->z_logical_clusterbits;
+		m->delta[0] = le16_to_cpu(di->di_u.delta[0]);
+		m->delta[1] = le16_to_cpu(di->di_u.delta[1]);
+		break;
+	case Z_EROFS_VLE_CLUSTER_TYPE_PLAIN:
+	case Z_EROFS_VLE_CLUSTER_TYPE_HEAD:
+		m->clusterofs = le16_to_cpu(di->di_clusterofs);
+		m->pblk = le32_to_cpu(di->di_u.blkaddr);
+		break;
+	default:
+		DBG_BUGON(1);
+		return -EOPNOTSUPP;
+	}
+	m->type = type;
+	return 0;
+}
+
+static unsigned int decode_compactedbits(unsigned int lobits,
+					 unsigned int lomask,
+					 u8 *in, unsigned int pos, u8 *type)
+{
+	const unsigned int v = get_unaligned_le32(in + pos / 8) >> (pos & 7);
+	const unsigned int lo = v & lomask;
+
+	*type = (v >> lobits) & 3;
+	return lo;
+}
+
+static int unpack_compacted_index(struct z_erofs_maprecorder *m,
+				  unsigned int amortizedshift,
+				  unsigned int eofs)
+{
+	struct erofs_inode *const vi = m->inode;
+	const unsigned int lclusterbits = vi->z_logical_clusterbits;
+	const unsigned int lomask = (1 << lclusterbits) - 1;
+	unsigned int vcnt, base, lo, encodebits, nblk;
+	int i;
+	u8 *in, type;
+
+	if (1 << amortizedshift == 4)
+		vcnt = 2;
+	else if (1 << amortizedshift == 2 && lclusterbits == 12)
+		vcnt = 16;
+	else
+		return -EOPNOTSUPP;
+
+	encodebits = ((vcnt << amortizedshift) - sizeof(__le32)) * 8 / vcnt;
+	base = round_down(eofs, vcnt << amortizedshift);
+	in = m->kaddr + base;
+
+	i = (eofs - base) >> amortizedshift;
+
+	lo = decode_compactedbits(lclusterbits, lomask,
+				  in, encodebits * i, &type);
+	m->type = type;
+	if (type == Z_EROFS_VLE_CLUSTER_TYPE_NONHEAD) {
+		m->clusterofs = 1 << lclusterbits;
+		if (i + 1 != (int)vcnt) {
+			m->delta[0] = lo;
+			return 0;
+		}
+		/*
+		 * since the last lcluster in the pack is special,
+		 * of which lo saves delta[1] rather than delta[0].
+		 * Hence, get delta[0] by the previous lcluster indirectly.
+		 */
+		lo = decode_compactedbits(lclusterbits, lomask,
+					  in, encodebits * (i - 1), &type);
+		if (type != Z_EROFS_VLE_CLUSTER_TYPE_NONHEAD)
+			lo = 0;
+		m->delta[0] = lo + 1;
+		return 0;
+	}
+	m->clusterofs = lo;
+	m->delta[0] = 0;
+	/* figout out blkaddr (pblk) for HEAD lclusters */
+	nblk = 1;
+	while (i > 0) {
+		--i;
+		lo = decode_compactedbits(lclusterbits, lomask,
+					  in, encodebits * i, &type);
+		if (type == Z_EROFS_VLE_CLUSTER_TYPE_NONHEAD)
+			i -= lo;
+
+		if (i >= 0)
+			++nblk;
+	}
+	in += (vcnt << amortizedshift) - sizeof(__le32);
+	m->pblk = le32_to_cpu(*(__le32 *)in) + nblk;
+	return 0;
+}
+
+static int compacted_load_cluster_from_disk(struct z_erofs_maprecorder *m,
+					    unsigned long lcn)
+{
+	struct erofs_inode *const vi = m->inode;
+	const unsigned int lclusterbits = vi->z_logical_clusterbits;
+	const erofs_off_t ebase = round_up(iloc(vi->nid) + vi->inode_isize +
+					   vi->xattr_isize, 8) +
+		sizeof(struct z_erofs_map_header);
+	const unsigned int totalidx = DIV_ROUND_UP(vi->i_size, EROFS_BLKSIZ);
+	unsigned int compacted_4b_initial, compacted_2b;
+	unsigned int amortizedshift;
+	erofs_off_t pos;
+	int err;
+
+	if (lclusterbits != 12)
+		return -EOPNOTSUPP;
+
+	if (lcn >= totalidx)
+		return -EINVAL;
+
+	m->lcn = lcn;
+	/* used to align to 32-byte (compacted_2b) alignment */
+	compacted_4b_initial = (32 - ebase % 32) / 4;
+	if (compacted_4b_initial == 32 / 4)
+		compacted_4b_initial = 0;
+
+	if (vi->z_advise & Z_EROFS_ADVISE_COMPACTED_2B)
+		compacted_2b = rounddown(totalidx - compacted_4b_initial, 16);
+	else
+		compacted_2b = 0;
+
+	pos = ebase;
+	if (lcn < compacted_4b_initial) {
+		amortizedshift = 2;
+		goto out;
+	}
+	pos += compacted_4b_initial * 4;
+	lcn -= compacted_4b_initial;
+
+	if (lcn < compacted_2b) {
+		amortizedshift = 1;
+		goto out;
+	}
+	pos += compacted_2b * 2;
+	lcn -= compacted_2b;
+	amortizedshift = 2;
+out:
+	pos += lcn * (1 << amortizedshift);
+	err = z_erofs_reload_indexes(m, erofs_blknr(pos));
+	if (err)
+		return err;
+	return unpack_compacted_index(m, amortizedshift, erofs_blkoff(pos));
+}
+
+static int z_erofs_load_cluster_from_disk(struct z_erofs_maprecorder *m,
+					  unsigned int lcn)
+{
+	const unsigned int datamode = m->inode->datalayout;
+
+	if (datamode == EROFS_INODE_FLAT_COMPRESSION_LEGACY)
+		return legacy_load_cluster_from_disk(m, lcn);
+
+	if (datamode == EROFS_INODE_FLAT_COMPRESSION)
+		return compacted_load_cluster_from_disk(m, lcn);
+
+	return -EINVAL;
+}
+
+static int z_erofs_extent_lookback(struct z_erofs_maprecorder *m,
+				   unsigned int lookback_distance)
+{
+	struct erofs_inode *const vi = m->inode;
+	struct erofs_map_blocks *const map = m->map;
+	const unsigned int lclusterbits = vi->z_logical_clusterbits;
+	unsigned long lcn = m->lcn;
+	int err;
+
+	if (lcn < lookback_distance) {
+		erofs_err("bogus lookback distance @ nid %llu",
+			  (unsigned long long)vi->nid);
+		DBG_BUGON(1);
+		return -EFSCORRUPTED;
+	}
+
+	/* load extent head logical cluster if needed */
+	lcn -= lookback_distance;
+	err = z_erofs_load_cluster_from_disk(m, lcn);
+	if (err)
+		return err;
+
+	switch (m->type) {
+	case Z_EROFS_VLE_CLUSTER_TYPE_NONHEAD:
+		if (!m->delta[0]) {
+			erofs_err("invalid lookback distance 0 @ nid %llu",
+				  (unsigned long long)vi->nid);
+			DBG_BUGON(1);
+			return -EFSCORRUPTED;
+		}
+		return z_erofs_extent_lookback(m, m->delta[0]);
+	case Z_EROFS_VLE_CLUSTER_TYPE_PLAIN:
+		map->m_flags &= ~EROFS_MAP_ZIPPED;
+	case Z_EROFS_VLE_CLUSTER_TYPE_HEAD:
+		map->m_la = (lcn << lclusterbits) | m->clusterofs;
+		break;
+	default:
+		erofs_err("unknown type %u @ lcn %lu of nid %llu",
+			  m->type, lcn, (unsigned long long)vi->nid);
+		DBG_BUGON(1);
+		return -EOPNOTSUPP;
+	}
+	return 0;
+}
+
+int z_erofs_map_blocks_iter(struct erofs_inode *vi,
+			    struct erofs_map_blocks *map)
+{
+	struct z_erofs_maprecorder m = {
+		.inode = vi,
+		.map = map,
+		.kaddr = map->mpage,
+	};
+	int err = 0;
+	unsigned int lclusterbits, endoff;
+	unsigned long long ofs, end;
+
+	/* when trying to read beyond EOF, leave it unmapped */
+	if (map->m_la >= vi->i_size) {
+		map->m_llen = map->m_la + 1 - vi->i_size;
+		map->m_la = vi->i_size;
+		map->m_flags = 0;
+		goto out;
+	}
+
+	err = z_erofs_fill_inode_lazy(vi);
+	if (err)
+		goto out;
+
+	lclusterbits = vi->z_logical_clusterbits;
+	ofs = map->m_la;
+	m.lcn = ofs >> lclusterbits;
+	endoff = ofs & ((1 << lclusterbits) - 1);
+
+	err = z_erofs_load_cluster_from_disk(&m, m.lcn);
+	if (err)
+		goto out;
+
+	map->m_flags = EROFS_MAP_ZIPPED;	/* by default, compressed */
+	end = (m.lcn + 1ULL) << lclusterbits;
+	switch (m.type) {
+	case Z_EROFS_VLE_CLUSTER_TYPE_PLAIN:
+		if (endoff >= m.clusterofs)
+			map->m_flags &= ~EROFS_MAP_ZIPPED;
+	case Z_EROFS_VLE_CLUSTER_TYPE_HEAD:
+		if (endoff >= m.clusterofs) {
+			map->m_la = (m.lcn << lclusterbits) | m.clusterofs;
+			break;
+		}
+		/* m.lcn should be >= 1 if endoff < m.clusterofs */
+		if (!m.lcn) {
+			erofs_err("invalid logical cluster 0 at nid %llu",
+				  (unsigned long long)vi->nid);
+			err = -EFSCORRUPTED;
+			goto out;
+		}
+		end = (m.lcn << lclusterbits) | m.clusterofs;
+		map->m_flags |= EROFS_MAP_FULL_MAPPED;
+		m.delta[0] = 1;
+	case Z_EROFS_VLE_CLUSTER_TYPE_NONHEAD:
+		/* get the correspoinding first chunk */
+		err = z_erofs_extent_lookback(&m, m.delta[0]);
+		if (err)
+			goto out;
+		break;
+	default:
+		erofs_err("unknown type %u @ offset %llu of nid %llu",
+			  m.type, ofs, (unsigned long long)vi->nid);
+		err = -EOPNOTSUPP;
+		goto out;
+	}
+
+	map->m_llen = end - map->m_la;
+	map->m_plen = 1 << lclusterbits;
+	map->m_pa = blknr_to_addr(m.pblk);
+	map->m_flags |= EROFS_MAP_MAPPED;
+
+out:
+	erofs_dbg("m_la %" PRIu64 " m_pa %" PRIu64 " m_llen %" PRIu64 " m_plen %" PRIu64 " m_flags 0%o",
+		  map->m_la, map->m_pa,
+		  map->m_llen, map->m_plen, map->m_flags);
+
+	DBG_BUGON(err < 0 && err != -ENOMEM);
+	return err;
+}
-- 
2.24.0

[PATCH v4 3/3] erofs-utils: fuse: add compressed file support

[Gao Xiang via Linux-erofs]

From: Huang Jianan <huangjianan@oppo.com>

This patch adds a simple approach (~ 700 LOC) to EROFS fixed-sized
output decompression without inplace I/O or decompression inplace
so it's easy to be ported everywhere with less constraint.

However, the on-disk compressed index parser (aka. zmap) is largely
kept in line with the kernel side, therefore new on-disk features
under development can be verified effectively first here.

Signed-off-by: Huang Jianan <huangjianan@oppo.com>
Signed-off-by: Guo Weichao <guoweichao@oppo.com>
Signed-off-by: Gao Xiang <hsiangkao@aol.com>
---
changes since v3:
 - fix build error without lz4 library.

 include/erofs/decompress.h |  35 ++++
 include/erofs/defs.h       |   5 +
 include/erofs/internal.h   |   8 +
 lib/Makefile.am            |   2 +-
 lib/data.c                 |  72 ++++++-
 lib/decompress.c           |  87 ++++++++
 lib/namei.c                |   4 +
 lib/zmap.c                 | 415 +++++++++++++++++++++++++++++++++++++
 8 files changed, 626 insertions(+), 2 deletions(-)
 create mode 100644 include/erofs/decompress.h
 create mode 100644 lib/decompress.c
 create mode 100644 lib/zmap.c

diff --git a/include/erofs/decompress.h b/include/erofs/decompress.h
new file mode 100644
index 000000000000..beaac359b21f
--- /dev/null
+++ b/include/erofs/decompress.h
@@ -0,0 +1,35 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * erofs-utils/include/erofs/decompress.h
+ *
+ * Copyright (C), 2008-2020, OPPO Mobile Comm Corp., Ltd.
+ * Created by Huang Jianan <huangjianan@oppo.com>
+ */
+#ifndef __EROFS_DECOMPRESS_H
+#define __EROFS_DECOMPRESS_H
+
+#include "internal.h"
+
+enum {
+	Z_EROFS_COMPRESSION_SHIFTED = Z_EROFS_COMPRESSION_MAX,
+	Z_EROFS_COMPRESSION_RUNTIME_MAX
+};
+
+struct z_erofs_decompress_req {
+	char *in, *out;
+
+	/*
+	 * initial decompressed bytes that need to be skipped
+	 * when finally copying to output buffer
+	 */
+	unsigned int decodedskip;
+	unsigned int inputsize, decodedlength;
+
+	/* indicate the algorithm will be used for decompression */
+	unsigned int alg;
+	bool partial_decoding;
+};
+
+int z_erofs_decompress(struct z_erofs_decompress_req *rq);
+
+#endif
diff --git a/include/erofs/defs.h b/include/erofs/defs.h
index 8dee661ab9f0..b54cd9d99981 100644
--- a/include/erofs/defs.h
+++ b/include/erofs/defs.h
@@ -170,5 +170,10 @@ typedef int64_t         s64;
 #define __maybe_unused      __attribute__((__unused__))
 #endif
 
+static inline u32 get_unaligned_le32(const u8 *p)
+{
+	return p[0] | p[1] << 8 | p[2] << 16 | p[3] << 24;
+}
+
 #endif
 
diff --git a/include/erofs/internal.h b/include/erofs/internal.h
index ec2646c23b78..bf13c166ba16 100644
--- a/include/erofs/internal.h
+++ b/include/erofs/internal.h
@@ -106,9 +106,13 @@ static inline void erofs_sb_clear_##name(void) \
 EROFS_FEATURE_FUNCS(lz4_0padding, incompat, INCOMPAT_LZ4_0PADDING)
 EROFS_FEATURE_FUNCS(sb_chksum, compat, COMPAT_SB_CHKSUM)
 
+#define EROFS_I_EA_INITED	(1 << 0)
+#define EROFS_I_Z_INITED	(1 << 1)
+
 struct erofs_inode {
 	struct list_head i_hash, i_subdirs, i_xattrs;
 
+	unsigned int flags;
 	unsigned int i_count;
 	struct erofs_inode *i_parent;
 
@@ -248,6 +252,10 @@ int erofs_ilookup(const char *path, struct erofs_inode *vi);
 /* data.c */
 int erofs_pread(struct erofs_inode *inode, char *buf,
 		erofs_off_t count, erofs_off_t offset);
+/* zmap.c */
+int z_erofs_fill_inode(struct erofs_inode *vi);
+int z_erofs_map_blocks_iter(struct erofs_inode *vi,
+			    struct erofs_map_blocks *map);
 
 #define EFSCORRUPTED	EUCLEAN		/* Filesystem is corrupted */
 
diff --git a/lib/Makefile.am b/lib/Makefile.am
index e1c43fa89009..f21dc35eda51 100644
--- a/lib/Makefile.am
+++ b/lib/Makefile.am
@@ -3,7 +3,7 @@
 
 noinst_LTLIBRARIES = liberofs.la
 liberofs_la_SOURCES = config.c io.c cache.c super.c inode.c xattr.c exclude.c \
-		      namei.c data.c compress.c compressor.c
+		      namei.c data.c compress.c compressor.c zmap.c decompress.c
 liberofs_la_CFLAGS = -Wall -Werror -I$(top_srcdir)/include
 if ENABLE_LZ4
 liberofs_la_CFLAGS += ${LZ4_CFLAGS}
diff --git a/lib/data.c b/lib/data.c
index 0337521f560e..3781846743aa 100644
--- a/lib/data.c
+++ b/lib/data.c
@@ -9,6 +9,7 @@
 #include "erofs/internal.h"
 #include "erofs/io.h"
 #include "erofs/trace.h"
+#include "erofs/decompress.h"
 
 static int erofs_map_blocks_flatmode(struct erofs_inode *inode,
 				     struct erofs_map_blocks *map,
@@ -116,6 +117,75 @@ static int erofs_read_raw_data(struct erofs_inode *inode, char *buffer,
 	return 0;
 }
 
+static int z_erofs_read_data(struct erofs_inode *inode, char *buffer,
+			     erofs_off_t size, erofs_off_t offset)
+{
+	int ret;
+	erofs_off_t end, length, skip;
+	struct erofs_map_blocks map = {
+		.index = UINT_MAX,
+	};
+	bool partial;
+	unsigned int algorithmformat;
+	char raw[EROFS_BLKSIZ];
+
+	end = offset + size;
+	while (end > offset) {
+		map.m_la = end - 1;
+
+		ret = z_erofs_map_blocks_iter(inode, &map);
+		if (ret)
+			return ret;
+
+		if (!(map.m_flags & EROFS_MAP_MAPPED)) {
+			end = map.m_la;
+			continue;
+		}
+
+		ret = dev_read(raw, map.m_pa, EROFS_BLKSIZ);
+		if (ret < 0)
+			return -EIO;
+
+		algorithmformat = map.m_flags & EROFS_MAP_ZIPPED ?
+						Z_EROFS_COMPRESSION_LZ4 :
+						Z_EROFS_COMPRESSION_SHIFTED;
+
+		/*
+		 * trim to the needed size if the returned extent is quite
+		 * larger than requested, and set up partial flag as well.
+		 */
+		if (end < map.m_la + map.m_llen) {
+			length = end - map.m_la;
+			partial = true;
+		} else {
+			DBG_BUGON(end != map.m_la + map.m_llen);
+			length = map.m_llen;
+			partial = !(map.m_flags & EROFS_MAP_FULL_MAPPED);
+		}
+
+		if (map.m_la < offset) {
+			skip = offset - map.m_la;
+			end = offset;
+		} else {
+			skip = 0;
+			end = map.m_la;
+		}
+
+		ret = z_erofs_decompress(&(struct z_erofs_decompress_req) {
+					.in = raw,
+					.out = buffer + end - offset,
+					.decodedskip = skip,
+					.inputsize = map.m_plen,
+					.decodedlength = length,
+					.alg = algorithmformat,
+					.partial_decoding = partial
+					 });
+		if (ret < 0)
+			return ret;
+	}
+	return 0;
+}
+
 int erofs_pread(struct erofs_inode *inode, char *buf,
 		erofs_off_t count, erofs_off_t offset)
 {
@@ -125,7 +195,7 @@ int erofs_pread(struct erofs_inode *inode, char *buf,
 		return erofs_read_raw_data(inode, buf, count, offset);
 	case EROFS_INODE_FLAT_COMPRESSION_LEGACY:
 	case EROFS_INODE_FLAT_COMPRESSION:
-		return -EOPNOTSUPP;
+		return z_erofs_read_data(inode, buf, count, offset);
 	default:
 		break;
 	}
diff --git a/lib/decompress.c b/lib/decompress.c
new file mode 100644
index 000000000000..870b85430dd1
--- /dev/null
+++ b/lib/decompress.c
@@ -0,0 +1,87 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * erofs-utils/lib/decompress.c
+ *
+ * Copyright (C), 2008-2020, OPPO Mobile Comm Corp., Ltd.
+ * Created by Huang Jianan <huangjianan@oppo.com>
+ */
+#include <stdlib.h>
+#include <lz4.h>
+
+#include "erofs/decompress.h"
+#include "erofs/err.h"
+
+#ifdef LZ4_ENABLED
+static int z_erofs_decompress_lz4(struct z_erofs_decompress_req *rq)
+{
+	int ret = 0;
+	char *dest = rq->out;
+	char *src = rq->in;
+	char *buff = NULL;
+	bool support_0padding = false;
+	unsigned int inputmargin = 0;
+
+	if (erofs_sb_has_lz4_0padding()) {
+		support_0padding = true;
+
+		while (!src[inputmargin & ~PAGE_MASK])
+			if (!(++inputmargin & ~PAGE_MASK))
+				break;
+
+		if (inputmargin >= rq->inputsize)
+			return -EIO;
+	}
+
+	if (rq->decodedskip) {
+		buff = malloc(rq->decodedlength);
+		if (!buff)
+			return -ENOMEM;
+		dest = buff;
+	}
+
+	if (rq->partial_decoding || !support_0padding)
+		ret = LZ4_decompress_safe_partial(src + inputmargin, dest,
+				rq->inputsize - inputmargin,
+				rq->decodedlength, rq->decodedlength);
+	else
+		ret = LZ4_decompress_safe(src + inputmargin, dest,
+					  rq->inputsize - inputmargin,
+					  rq->decodedlength);
+
+	if (ret != (int)rq->decodedlength) {
+		ret = -EIO;
+		goto out;
+	}
+
+	if (rq->decodedskip)
+		memcpy(rq->out, dest + rq->decodedskip,
+		       rq->decodedlength - rq->decodedskip);
+
+out:
+	if (buff)
+		free(buff);
+
+	return ret;
+}
+#endif
+
+int z_erofs_decompress(struct z_erofs_decompress_req *rq)
+{
+	if (rq->alg == Z_EROFS_COMPRESSION_SHIFTED) {
+		if (rq->inputsize != EROFS_BLKSIZ)
+			return -EFSCORRUPTED;
+
+		DBG_BUGON(rq->decodedlength > EROFS_BLKSIZ);
+		DBG_BUGON(rq->decodedlength < rq->decodedskip);
+
+		memcpy(rq->out, rq->in + rq->decodedskip,
+		       rq->decodedlength - rq->decodedskip);
+		return 0;
+	}
+
+#ifdef LZ4_ENABLED
+	if (rq->alg == Z_EROFS_COMPRESSION_LZ4)
+		return z_erofs_decompress_lz4(rq);
+#endif
+	return -EOPNOTSUPP;
+}
diff --git a/lib/namei.c b/lib/namei.c
index e8275a42f090..4e06ba468dc4 100644
--- a/lib/namei.c
+++ b/lib/namei.c
@@ -122,6 +122,10 @@ static int erofs_read_inode_from_disk(struct erofs_inode *vi)
 			  erofs_inode_version(ifmt), vi->nid | 0ULL);
 		return -EOPNOTSUPP;
 	}
+
+	vi->flags = 0;
+	if (erofs_inode_is_data_compressed(vi->datalayout))
+		z_erofs_fill_inode(vi);
 	return 0;
 bogusimode:
 	erofs_err("bogus i_mode (%o) @ nid %llu", vi->i_mode, vi->nid | 0ULL);
diff --git a/lib/zmap.c b/lib/zmap.c
new file mode 100644
index 000000000000..ee63de74cab2
--- /dev/null
+++ b/lib/zmap.c
@@ -0,0 +1,415 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * erofs-utils/lib/zmap.c
+ *
+ * (a large amount of code was adapted from Linux kernel. )
+ *
+ * Copyright (C) 2018-2019 HUAWEI, Inc.
+ *             https://www.huawei.com/
+ * Created by Gao Xiang <gaoxiang25@huawei.com>
+ * Modified by Huang Jianan <huangjianan@oppo.com>
+ */
+#include "erofs/io.h"
+#include "erofs/print.h"
+
+int z_erofs_fill_inode(struct erofs_inode *vi)
+{
+	if (vi->datalayout == EROFS_INODE_FLAT_COMPRESSION_LEGACY) {
+		vi->z_advise = 0;
+		vi->z_algorithmtype[0] = 0;
+		vi->z_algorithmtype[1] = 0;
+		vi->z_logical_clusterbits = LOG_BLOCK_SIZE;
+		vi->z_physical_clusterbits[0] = vi->z_logical_clusterbits;
+		vi->z_physical_clusterbits[1] = vi->z_logical_clusterbits;
+
+		vi->flags |= EROFS_I_Z_INITED;
+	}
+	return 0;
+}
+
+static int z_erofs_fill_inode_lazy(struct erofs_inode *vi)
+{
+	int ret;
+	erofs_off_t pos;
+	struct z_erofs_map_header *h;
+	char buf[sizeof(struct z_erofs_map_header)];
+
+	if (vi->flags & EROFS_I_Z_INITED)
+		return 0;
+
+	DBG_BUGON(vi->datalayout == EROFS_INODE_FLAT_COMPRESSION_LEGACY);
+	pos = round_up(iloc(vi->nid) + vi->inode_isize + vi->xattr_isize, 8);
+
+	ret = dev_read(buf, pos, sizeof(buf));
+	if (ret < 0)
+		return -EIO;
+
+	h = (struct z_erofs_map_header *)buf;
+	vi->z_advise = le16_to_cpu(h->h_advise);
+	vi->z_algorithmtype[0] = h->h_algorithmtype & 15;
+	vi->z_algorithmtype[1] = h->h_algorithmtype >> 4;
+
+	if (vi->z_algorithmtype[0] >= Z_EROFS_COMPRESSION_MAX) {
+		erofs_err("unknown compression format %u for nid %llu",
+			  vi->z_algorithmtype[0], (unsigned long long)vi->nid);
+		return -EOPNOTSUPP;
+	}
+
+	vi->z_logical_clusterbits = LOG_BLOCK_SIZE + (h->h_clusterbits & 7);
+	vi->z_physical_clusterbits[0] = vi->z_logical_clusterbits +
+					((h->h_clusterbits >> 3) & 3);
+
+	if (vi->z_physical_clusterbits[0] != LOG_BLOCK_SIZE) {
+		erofs_err("unsupported physical clusterbits %u for nid %llu",
+			  vi->z_physical_clusterbits[0], (unsigned long long)vi->nid);
+		return -EOPNOTSUPP;
+	}
+
+	vi->z_physical_clusterbits[1] = vi->z_logical_clusterbits +
+					((h->h_clusterbits >> 5) & 7);
+	vi->flags |= EROFS_I_Z_INITED;
+	return 0;
+}
+
+struct z_erofs_maprecorder {
+	struct erofs_inode *inode;
+	struct erofs_map_blocks *map;
+	void *kaddr;
+
+	unsigned long lcn;
+	/* compression extent information gathered */
+	u8  type;
+	u16 clusterofs;
+	u16 delta[2];
+	erofs_blk_t pblk;
+};
+
+static int z_erofs_reload_indexes(struct z_erofs_maprecorder *m,
+				  erofs_blk_t eblk)
+{
+	int ret;
+	struct erofs_map_blocks *const map = m->map;
+	char *mpage = map->mpage;
+
+	if (map->index == eblk)
+		return 0;
+
+	ret = blk_read(mpage, eblk, 1);
+	if (ret < 0)
+		return -EIO;
+
+	map->index = eblk;
+
+	return 0;
+}
+
+static int legacy_load_cluster_from_disk(struct z_erofs_maprecorder *m,
+					 unsigned long lcn)
+{
+	struct erofs_inode *const vi = m->inode;
+	const erofs_off_t ibase = iloc(vi->nid);
+	const erofs_off_t pos =
+		Z_EROFS_VLE_LEGACY_INDEX_ALIGN(ibase + vi->inode_isize +
+					       vi->xattr_isize) +
+		lcn * sizeof(struct z_erofs_vle_decompressed_index);
+	struct z_erofs_vle_decompressed_index *di;
+	unsigned int advise, type;
+	int err;
+
+	err = z_erofs_reload_indexes(m, erofs_blknr(pos));
+	if (err)
+		return err;
+
+	m->lcn = lcn;
+	di = m->kaddr + erofs_blkoff(pos);
+
+	advise = le16_to_cpu(di->di_advise);
+	type = (advise >> Z_EROFS_VLE_DI_CLUSTER_TYPE_BIT) &
+		((1 << Z_EROFS_VLE_DI_CLUSTER_TYPE_BITS) - 1);
+	switch (type) {
+	case Z_EROFS_VLE_CLUSTER_TYPE_NONHEAD:
+		m->clusterofs = 1 << vi->z_logical_clusterbits;
+		m->delta[0] = le16_to_cpu(di->di_u.delta[0]);
+		m->delta[1] = le16_to_cpu(di->di_u.delta[1]);
+		break;
+	case Z_EROFS_VLE_CLUSTER_TYPE_PLAIN:
+	case Z_EROFS_VLE_CLUSTER_TYPE_HEAD:
+		m->clusterofs = le16_to_cpu(di->di_clusterofs);
+		m->pblk = le32_to_cpu(di->di_u.blkaddr);
+		break;
+	default:
+		DBG_BUGON(1);
+		return -EOPNOTSUPP;
+	}
+	m->type = type;
+	return 0;
+}
+
+static unsigned int decode_compactedbits(unsigned int lobits,
+					 unsigned int lomask,
+					 u8 *in, unsigned int pos, u8 *type)
+{
+	const unsigned int v = get_unaligned_le32(in + pos / 8) >> (pos & 7);
+	const unsigned int lo = v & lomask;
+
+	*type = (v >> lobits) & 3;
+	return lo;
+}
+
+static int unpack_compacted_index(struct z_erofs_maprecorder *m,
+				  unsigned int amortizedshift,
+				  unsigned int eofs)
+{
+	struct erofs_inode *const vi = m->inode;
+	const unsigned int lclusterbits = vi->z_logical_clusterbits;
+	const unsigned int lomask = (1 << lclusterbits) - 1;
+	unsigned int vcnt, base, lo, encodebits, nblk;
+	int i;
+	u8 *in, type;
+
+	if (1 << amortizedshift == 4)
+		vcnt = 2;
+	else if (1 << amortizedshift == 2 && lclusterbits == 12)
+		vcnt = 16;
+	else
+		return -EOPNOTSUPP;
+
+	encodebits = ((vcnt << amortizedshift) - sizeof(__le32)) * 8 / vcnt;
+	base = round_down(eofs, vcnt << amortizedshift);
+	in = m->kaddr + base;
+
+	i = (eofs - base) >> amortizedshift;
+
+	lo = decode_compactedbits(lclusterbits, lomask,
+				  in, encodebits * i, &type);
+	m->type = type;
+	if (type == Z_EROFS_VLE_CLUSTER_TYPE_NONHEAD) {
+		m->clusterofs = 1 << lclusterbits;
+		if (i + 1 != (int)vcnt) {
+			m->delta[0] = lo;
+			return 0;
+		}
+		/*
+		 * since the last lcluster in the pack is special,
+		 * of which lo saves delta[1] rather than delta[0].
+		 * Hence, get delta[0] by the previous lcluster indirectly.
+		 */
+		lo = decode_compactedbits(lclusterbits, lomask,
+					  in, encodebits * (i - 1), &type);
+		if (type != Z_EROFS_VLE_CLUSTER_TYPE_NONHEAD)
+			lo = 0;
+		m->delta[0] = lo + 1;
+		return 0;
+	}
+	m->clusterofs = lo;
+	m->delta[0] = 0;
+	/* figout out blkaddr (pblk) for HEAD lclusters */
+	nblk = 1;
+	while (i > 0) {
+		--i;
+		lo = decode_compactedbits(lclusterbits, lomask,
+					  in, encodebits * i, &type);
+		if (type == Z_EROFS_VLE_CLUSTER_TYPE_NONHEAD)
+			i -= lo;
+
+		if (i >= 0)
+			++nblk;
+	}
+	in += (vcnt << amortizedshift) - sizeof(__le32);
+	m->pblk = le32_to_cpu(*(__le32 *)in) + nblk;
+	return 0;
+}
+
+static int compacted_load_cluster_from_disk(struct z_erofs_maprecorder *m,
+					    unsigned long lcn)
+{
+	struct erofs_inode *const vi = m->inode;
+	const unsigned int lclusterbits = vi->z_logical_clusterbits;
+	const erofs_off_t ebase = round_up(iloc(vi->nid) + vi->inode_isize +
+					   vi->xattr_isize, 8) +
+		sizeof(struct z_erofs_map_header);
+	const unsigned int totalidx = DIV_ROUND_UP(vi->i_size, EROFS_BLKSIZ);
+	unsigned int compacted_4b_initial, compacted_2b;
+	unsigned int amortizedshift;
+	erofs_off_t pos;
+	int err;
+
+	if (lclusterbits != 12)
+		return -EOPNOTSUPP;
+
+	if (lcn >= totalidx)
+		return -EINVAL;
+
+	m->lcn = lcn;
+	/* used to align to 32-byte (compacted_2b) alignment */
+	compacted_4b_initial = (32 - ebase % 32) / 4;
+	if (compacted_4b_initial == 32 / 4)
+		compacted_4b_initial = 0;
+
+	if (vi->z_advise & Z_EROFS_ADVISE_COMPACTED_2B)
+		compacted_2b = rounddown(totalidx - compacted_4b_initial, 16);
+	else
+		compacted_2b = 0;
+
+	pos = ebase;
+	if (lcn < compacted_4b_initial) {
+		amortizedshift = 2;
+		goto out;
+	}
+	pos += compacted_4b_initial * 4;
+	lcn -= compacted_4b_initial;
+
+	if (lcn < compacted_2b) {
+		amortizedshift = 1;
+		goto out;
+	}
+	pos += compacted_2b * 2;
+	lcn -= compacted_2b;
+	amortizedshift = 2;
+out:
+	pos += lcn * (1 << amortizedshift);
+	err = z_erofs_reload_indexes(m, erofs_blknr(pos));
+	if (err)
+		return err;
+	return unpack_compacted_index(m, amortizedshift, erofs_blkoff(pos));
+}
+
+static int z_erofs_load_cluster_from_disk(struct z_erofs_maprecorder *m,
+					  unsigned int lcn)
+{
+	const unsigned int datamode = m->inode->datalayout;
+
+	if (datamode == EROFS_INODE_FLAT_COMPRESSION_LEGACY)
+		return legacy_load_cluster_from_disk(m, lcn);
+
+	if (datamode == EROFS_INODE_FLAT_COMPRESSION)
+		return compacted_load_cluster_from_disk(m, lcn);
+
+	return -EINVAL;
+}
+
+static int z_erofs_extent_lookback(struct z_erofs_maprecorder *m,
+				   unsigned int lookback_distance)
+{
+	struct erofs_inode *const vi = m->inode;
+	struct erofs_map_blocks *const map = m->map;
+	const unsigned int lclusterbits = vi->z_logical_clusterbits;
+	unsigned long lcn = m->lcn;
+	int err;
+
+	if (lcn < lookback_distance) {
+		erofs_err("bogus lookback distance @ nid %llu",
+			  (unsigned long long)vi->nid);
+		DBG_BUGON(1);
+		return -EFSCORRUPTED;
+	}
+
+	/* load extent head logical cluster if needed */
+	lcn -= lookback_distance;
+	err = z_erofs_load_cluster_from_disk(m, lcn);
+	if (err)
+		return err;
+
+	switch (m->type) {
+	case Z_EROFS_VLE_CLUSTER_TYPE_NONHEAD:
+		if (!m->delta[0]) {
+			erofs_err("invalid lookback distance 0 @ nid %llu",
+				  (unsigned long long)vi->nid);
+			DBG_BUGON(1);
+			return -EFSCORRUPTED;
+		}
+		return z_erofs_extent_lookback(m, m->delta[0]);
+	case Z_EROFS_VLE_CLUSTER_TYPE_PLAIN:
+		map->m_flags &= ~EROFS_MAP_ZIPPED;
+	case Z_EROFS_VLE_CLUSTER_TYPE_HEAD:
+		map->m_la = (lcn << lclusterbits) | m->clusterofs;
+		break;
+	default:
+		erofs_err("unknown type %u @ lcn %lu of nid %llu",
+			  m->type, lcn, (unsigned long long)vi->nid);
+		DBG_BUGON(1);
+		return -EOPNOTSUPP;
+	}
+	return 0;
+}
+
+int z_erofs_map_blocks_iter(struct erofs_inode *vi,
+			    struct erofs_map_blocks *map)
+{
+	struct z_erofs_maprecorder m = {
+		.inode = vi,
+		.map = map,
+		.kaddr = map->mpage,
+	};
+	int err = 0;
+	unsigned int lclusterbits, endoff;
+	unsigned long long ofs, end;
+
+	/* when trying to read beyond EOF, leave it unmapped */
+	if (map->m_la >= vi->i_size) {
+		map->m_llen = map->m_la + 1 - vi->i_size;
+		map->m_la = vi->i_size;
+		map->m_flags = 0;
+		goto out;
+	}
+
+	err = z_erofs_fill_inode_lazy(vi);
+	if (err)
+		goto out;
+
+	lclusterbits = vi->z_logical_clusterbits;
+	ofs = map->m_la;
+	m.lcn = ofs >> lclusterbits;
+	endoff = ofs & ((1 << lclusterbits) - 1);
+
+	err = z_erofs_load_cluster_from_disk(&m, m.lcn);
+	if (err)
+		goto out;
+
+	map->m_flags = EROFS_MAP_ZIPPED;	/* by default, compressed */
+	end = (m.lcn + 1ULL) << lclusterbits;
+	switch (m.type) {
+	case Z_EROFS_VLE_CLUSTER_TYPE_PLAIN:
+		if (endoff >= m.clusterofs)
+			map->m_flags &= ~EROFS_MAP_ZIPPED;
+	case Z_EROFS_VLE_CLUSTER_TYPE_HEAD:
+		if (endoff >= m.clusterofs) {
+			map->m_la = (m.lcn << lclusterbits) | m.clusterofs;
+			break;
+		}
+		/* m.lcn should be >= 1 if endoff < m.clusterofs */
+		if (!m.lcn) {
+			erofs_err("invalid logical cluster 0 at nid %llu",
+				  (unsigned long long)vi->nid);
+			err = -EFSCORRUPTED;
+			goto out;
+		}
+		end = (m.lcn << lclusterbits) | m.clusterofs;
+		map->m_flags |= EROFS_MAP_FULL_MAPPED;
+		m.delta[0] = 1;
+	case Z_EROFS_VLE_CLUSTER_TYPE_NONHEAD:
+		/* get the correspoinding first chunk */
+		err = z_erofs_extent_lookback(&m, m.delta[0]);
+		if (err)
+			goto out;
+		break;
+	default:
+		erofs_err("unknown type %u @ offset %llu of nid %llu",
+			  m.type, ofs, (unsigned long long)vi->nid);
+		err = -EOPNOTSUPP;
+		goto out;
+	}
+
+	map->m_llen = end - map->m_la;
+	map->m_plen = 1 << lclusterbits;
+	map->m_pa = blknr_to_addr(m.pblk);
+	map->m_flags |= EROFS_MAP_MAPPED;
+
+out:
+	erofs_dbg("m_la %" PRIu64 " m_pa %" PRIu64 " m_llen %" PRIu64 " m_plen %" PRIu64 " m_flags 0%o",
+		  map->m_la, map->m_pa,
+		  map->m_llen, map->m_plen, map->m_flags);
+
+	DBG_BUGON(err < 0 && err != -ENOMEM);
+	return err;
+}
-- 
2.24.0

Re: [PATCH v4 3/3] erofs-utils: fuse: add compressed file support

[Li GuiFu via Linux-erofs]

On 2020/11/27 20:24, Gao Xiang via Linux-erofs wrote:
> From: Huang Jianan <huangjianan@oppo.com>
> 
> This patch adds a simple approach (~ 700 LOC) to EROFS fixed-sized
> output decompression without inplace I/O or decompression inplace
> so it's easy to be ported everywhere with less constraint.
> 
> However, the on-disk compressed index parser (aka. zmap) is largely
> kept in line with the kernel side, therefore new on-disk features
> under development can be verified effectively first here.
> 
> Signed-off-by: Huang Jianan <huangjianan@oppo.com>
> Signed-off-by: Guo Weichao <guoweichao@oppo.com>
> Signed-off-by: Gao Xiang <hsiangkao@aol.com>
> ---
> changes since v3:
>  - fix build error without lz4 library.
> 
>  include/erofs/decompress.h |  35 ++++
>  include/erofs/defs.h       |   5 +
>  include/erofs/internal.h   |   8 +
>  lib/Makefile.am            |   2 +-
>  lib/data.c                 |  72 ++++++-
>  lib/decompress.c           |  87 ++++++++
>  lib/namei.c                |   4 +
>  lib/zmap.c                 | 415 +++++++++++++++++++++++++++++++++++++
>  8 files changed, 626 insertions(+), 2 deletions(-)
>  create mode 100644 include/erofs/decompress.h
>  create mode 100644 lib/decompress.c
>  create mode 100644 lib/zmap.c
> 

It looks good
Reviewed-by: Li Guifu <bluce.lee@aliyun.com>
Tested-by: Li Guifu <bluce.lee@aliyun.com>
Thanks,

Re: [PATCH v3 0/3] erofs-utils: introduce fuse implementation

[Gao Xiang]

On Fri, Nov 27, 2020 at 07:46:14PM +0800, Gao Xiang via Linux-erofs wrote:
> From: Gao Xiang <hsiangkao@redhat.com>
> 
> changes since v2:
>  - erofs_dbg() -> erofs_dump() in signal_handle_sigsegv() (Guifu);
>  - get rid of unnecessary new lines (Guifu).
> 
> changes since v1:
>  - fix off-by-one error of namebuf in erofs_fill_dentries();
>  - drop unused "struct erofs_super_block super;" in lib/super.c; 
>  - fix clang/32-bit build errors founded by travis CI.

FYI, I will apply this to dev branch since it has been of some
preliminary deployment by some vendor, plus it's disabled
by default for the upcoming erofs-utils 1.2. And it's already
in shape after several rounds cleanup.

I'm looking into and will add more automated testcase coverage
for this stuff.

Incremental bugfixes / improvements for erofsfuse are always
welcome!

Thanks,
Gao Xiang