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From: Omar Sandoval <osandov@osandov.com>
To: linux-btrfs@vger.kernel.org
Cc: linux-fsdevel@vger.kernel.org, kernel-team@fb.com
Subject: [PATCH v3 05/11] btrfs-progs: receive: add stub implementation for pwritev2
Date: Fri, 22 Jan 2021 12:47:51 -0800	[thread overview]
Message-ID: <e0d2c6c86a5b76db21620443ed6f66a4c2a7c30e.1611347859.git.osandov@osandov.com> (raw)
In-Reply-To: <cover.1611347187.git.osandov@fb.com>

From: Boris Burkov <borisb@fb.com>

Encoded writes in receive will use pwritev2. It is possible that the
system libc does not export this function, so we stub it out and detect
whether to build the stub code with autoconf.

This syscall has special semantics in x32 (no hi lo, just takes loff_t)
so we have to detect that case and use the appropriate arguments.

Signed-off-by: Boris Burkov <boris@bur.io>
---
 Makefile     |  4 ++--
 configure.ac |  1 +
 stubs.c      | 24 ++++++++++++++++++++++++
 stubs.h      | 11 +++++++++++
 4 files changed, 38 insertions(+), 2 deletions(-)
 create mode 100644 stubs.c
 create mode 100644 stubs.h

diff --git a/Makefile b/Makefile
index e288a336..7c0971f7 100644
--- a/Makefile
+++ b/Makefile
@@ -173,12 +173,12 @@ libbtrfs_objects = common/send-stream.o common/send-utils.o kernel-lib/rbtree.o
 		   kernel-lib/raid56.o kernel-lib/tables.o \
 		   common/device-scan.o common/path-utils.o \
 		   common/utils.o libbtrfsutil/subvolume.o libbtrfsutil/stubs.o \
-		   crypto/hash.o crypto/xxhash.o $(CRYPTO_OBJECTS)
+		   crypto/hash.o crypto/xxhash.o $(CRYPTO_OBJECTS) stubs.o
 libbtrfs_headers = common/send-stream.h common/send-utils.h send.h kernel-lib/rbtree.h btrfs-list.h \
 	       crypto/crc32c.h kernel-lib/list.h kerncompat.h \
 	       kernel-lib/radix-tree.h kernel-lib/sizes.h kernel-lib/raid56.h \
 	       common/extent-cache.h kernel-shared/extent_io.h ioctl.h \
-	       kernel-shared/ctree.h btrfsck.h version.h
+	       kernel-shared/ctree.h btrfsck.h version.h stubs.h
 libbtrfsutil_major := $(shell sed -rn 's/^\#define BTRFS_UTIL_VERSION_MAJOR ([0-9])+$$/\1/p' libbtrfsutil/btrfsutil.h)
 libbtrfsutil_minor := $(shell sed -rn 's/^\#define BTRFS_UTIL_VERSION_MINOR ([0-9])+$$/\1/p' libbtrfsutil/btrfsutil.h)
 libbtrfsutil_patch := $(shell sed -rn 's/^\#define BTRFS_UTIL_VERSION_PATCH ([0-9])+$$/\1/p' libbtrfsutil/btrfsutil.h)
diff --git a/configure.ac b/configure.ac
index 39f93040..d43eb91f 100644
--- a/configure.ac
+++ b/configure.ac
@@ -57,6 +57,7 @@ AC_CHECK_FUNCS([openat], [],
 	[AC_MSG_ERROR([cannot find openat() function])])
 
 AC_CHECK_FUNCS([reallocarray])
+AC_CHECK_FUNCS([pwritev2])
 
 m4_ifndef([PKG_PROG_PKG_CONFIG],
   [m4_fatal([Could not locate the pkg-config autoconf
diff --git a/stubs.c b/stubs.c
new file mode 100644
index 00000000..ab68a411
--- /dev/null
+++ b/stubs.c
@@ -0,0 +1,24 @@
+#if HAVE_PWRITEV2 != 1
+
+#include "stubs.h"
+
+#include "kerncompat.h"
+
+#include <unistd.h>
+#include <sys/syscall.h>
+#include <sys/uio.h>
+
+ssize_t pwritev2(int fd, const struct iovec *iov, int iovcnt, off_t offset,
+		 int flags)
+{
+/* these conditions indicate an x32 system, which has a different pwritev2 */
+#if defined(__x86_64__) && defined(__ILP32__)
+	return syscall(SYS_pwritev2, fd, iov, iovcnt, offset, flags);
+#else
+	unsigned long hi = offset >> (BITS_PER_LONG / 2) >> (BITS_PER_LONG / 2);
+	unsigned long lo = offset;
+
+	return syscall(SYS_pwritev2, fd, iov, iovcnt, lo, hi, flags);
+#endif // X32
+}
+#endif /* HAVE_PWRIVEV2 */
diff --git a/stubs.h b/stubs.h
new file mode 100644
index 00000000..b39f8a69
--- /dev/null
+++ b/stubs.h
@@ -0,0 +1,11 @@
+#ifndef _BTRFS_STUBS_H
+#define _BTRFS_STUBS_H
+
+#include <sys/types.h>
+
+struct iovec;
+
+ssize_t pwritev2(int fd, const struct iovec *iov, int iovcnt, off_t offset,
+		 int flags);
+
+#endif
-- 
2.30.0


  parent reply	other threads:[~2021-01-22 21:11 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-22 20:47 [PATCH v3 0/5] btrfs: implement send/receive of compressed extents without decompressing Omar Sandoval
2021-01-22 20:47 ` [PATCH v3 1/5] btrfs: add send stream v2 definitions Omar Sandoval
2021-01-22 20:47 ` [PATCH v3 01/11] btrfs-progs: receive: support v2 send stream larger tlv_len Omar Sandoval
2021-01-22 20:47 ` [PATCH v3 02/11] btrfs-progs: receive: dynamically allocate sctx->read_buf Omar Sandoval
2021-01-22 20:47 ` [PATCH v3 2/5] btrfs: send: write larger chunks when using stream v2 Omar Sandoval
2021-01-22 20:47 ` [PATCH v3 03/11] btrfs-progs: receive: support v2 send stream DATA tlv format Omar Sandoval
2021-01-22 20:47 ` [PATCH v3 3/5] btrfs: send: allocate send buffer with alloc_page() and vmap() for v2 Omar Sandoval
2021-01-22 20:47 ` [PATCH v3 04/11] btrfs-progs: receive: add send stream v2 cmds and attrs to send.h Omar Sandoval
2021-01-22 20:47 ` [PATCH v3 4/5] btrfs: send: send compressed extents with encoded writes Omar Sandoval
2021-01-22 20:47 ` Omar Sandoval [this message]
2021-01-22 20:47 ` [PATCH v3 5/5] btrfs: send: enable support for stream v2 and compressed writes Omar Sandoval
2021-01-22 20:47 ` [PATCH v3 06/11] btrfs-progs: receive: process encoded_write commands Omar Sandoval
2021-01-22 20:47 ` [PATCH v3 07/11] btrfs-progs: receive: encoded_write fallback to explicit decode and write Omar Sandoval
2021-01-22 20:47 ` [PATCH v3 08/11] btrfs-progs: receive: process fallocate commands Omar Sandoval
2021-01-22 20:47 ` [PATCH v3 09/11] btrfs-progs: receive: process setflags ioctl commands Omar Sandoval
2021-01-22 20:47 ` [PATCH v3 10/11] btrfs-progs: send: stream v2 ioctl flags Omar Sandoval
2021-01-22 20:47 ` [PATCH v3 11/11] btrfs-progs: receive: add tests for basic encoded_write send/receive Omar Sandoval

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