[xfsprogs PATCH v4 0/2] Add necessary items for MAP_SYNC testing

[xfsprogs PATCH v4 0/2] Add necessary items for MAP_SYNC testing

[Ross Zwisler]

This is the fourth revision of my MAP_SYNC + dm-log-writes support for
xfsprogs.  The previous revision can be found here:

https://lists.01.org/pipermail/linux-nvdimm/2017-December/013473.html

Changes since v3:

 - Fixed indentation of variable declarations (Darrick).

 - Added a comment for the case where MAP_SYNC and MAP_SHARED_VALIDATE
   aren't defined in system headers and we fail an msync command
   (Darrick).
 
 - Dropped patch 1 of the previous series which fixed compiler warnings.
   A fix for this issue was already submitted by Dave.

---

As suggested by Dave Chinner:

    As I say to all these sorts of one-off test prgrams: please add the
    new MAP_SYNC flag to xfs_io rather than writing a one-off
    test program to set it and write some data.

    And if we're going to be adding special custom tests just because
    we need to insert dm-log marks, add that functionality to xfs_io,
    too.

    That way we can create complex custom dm logwrite tests without
    needing one-off test programs for them all...

This series enhances xfs_io by adding support for the MAP_SYNC mmap() flag
and for dm-log-writes marks.  This allows the resulting xfstest for
MAP_SYNC to be much simpler and have no custom C programs.

Ross Zwisler (2):
  xfs_io: add MAP_SYNC support to mmap()
  xfs_io: add a new 'log_writes' command

 configure.ac            |   2 +
 debian/control          |   2 +-
 include/builddefs.in    |   3 ++
 include/linux.h         |   8 ++++
 io/Makefile             |  10 +++++
 io/init.c               |   1 +
 io/io.h                 |   7 ++++
 io/log_writes.c         | 106 ++++++++++++++++++++++++++++++++++++++++++++++++
 io/mmap.c               |  29 ++++++++++---
 m4/Makefile             |   1 +
 m4/package_devmapper.m4 |  11 +++++
 m4/package_libcdev.m4   |  16 ++++++++
 man/man8/xfs_io.8       |  29 ++++++++++++-
 13 files changed, 217 insertions(+), 8 deletions(-)
 create mode 100644 io/log_writes.c
 create mode 100644 m4/package_devmapper.m4

-- 
2.14.3

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[xfsprogs PATCH v4 1/2] xfs_io: add MAP_SYNC support to mmap()

[Ross Zwisler]

Add support for a new -S flag to xfs_io's mmap command.  This opens the
mapping with the (MAP_SYNC | MAP_SHARED_VALIDATE) flags instead of the
standard MAP_SHARED flag.

Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Suggested-by: Dave Chinner <david@fromorbit.com>
---
 configure.ac          |  1 +
 include/builddefs.in  |  1 +
 include/linux.h       |  8 ++++++++
 io/Makefile           |  4 ++++
 io/io.h               |  1 +
 io/mmap.c             | 29 ++++++++++++++++++++++++-----
 m4/package_libcdev.m4 | 16 ++++++++++++++++
 man/man8/xfs_io.8     |  6 +++++-
 8 files changed, 60 insertions(+), 6 deletions(-)

diff --git a/configure.ac b/configure.ac
index e5d0309f..f3325aa0 100644
--- a/configure.ac
+++ b/configure.ac
@@ -163,6 +163,7 @@ AC_HAVE_MREMAP
 AC_NEED_INTERNAL_FSXATTR
 AC_HAVE_GETFSMAP
 AC_HAVE_STATFS_FLAGS
+AC_HAVE_MAP_SYNC
 
 if test "$enable_blkid" = yes; then
 AC_HAVE_BLKID_TOPO
diff --git a/include/builddefs.in b/include/builddefs.in
index fd274ddc..126f7e95 100644
--- a/include/builddefs.in
+++ b/include/builddefs.in
@@ -115,6 +115,7 @@ HAVE_MREMAP = @have_mremap@
 NEED_INTERNAL_FSXATTR = @need_internal_fsxattr@
 HAVE_GETFSMAP = @have_getfsmap@
 HAVE_STATFS_FLAGS = @have_statfs_flags@
+HAVE_MAP_SYNC = @have_map_sync@
 
 GCCFLAGS = -funsigned-char -fno-strict-aliasing -Wall
 #	   -Wbitwise -Wno-transparent-union -Wno-old-initializer -Wno-decl
diff --git a/include/linux.h b/include/linux.h
index 6ce344c5..1998941a 100644
--- a/include/linux.h
+++ b/include/linux.h
@@ -327,4 +327,12 @@ fsmap_advance(
 #define HAVE_GETFSMAP
 #endif /* HAVE_GETFSMAP */
 
+#ifndef HAVE_MAP_SYNC
+#define MAP_SYNC 0
+#define MAP_SHARED_VALIDATE 0
+#else
+#include <asm-generic/mman.h>
+#include <asm-generic/mman-common.h>
+#endif /* HAVE_MAP_SYNC */
+
 #endif	/* __XFS_LINUX_H__ */
diff --git a/io/Makefile b/io/Makefile
index 6725936d..2987ee11 100644
--- a/io/Makefile
+++ b/io/Makefile
@@ -103,6 +103,10 @@ ifeq ($(HAVE_MREMAP),yes)
 LCFLAGS += -DHAVE_MREMAP
 endif
 
+ifeq ($(HAVE_MAP_SYNC),yes)
+LCFLAGS += -DHAVE_MAP_SYNC
+endif
+
 # On linux we get fsmap from the system or define it ourselves
 # so include this based on platform type.  If this reverts to only
 # the autoconf check w/o local definition, change to testing HAVE_GETFSMAP
diff --git a/io/io.h b/io/io.h
index 3862985f..8b2753b3 100644
--- a/io/io.h
+++ b/io/io.h
@@ -65,6 +65,7 @@ typedef struct mmap_region {
 	size_t		length;		/* length of mapping */
 	off64_t		offset;		/* start offset into backing file */
 	int		prot;		/* protection mode of the mapping */
+	bool		map_sync;	/* is this a MAP_SYNC mapping? */
 	char		*name;		/* name of backing file */
 } mmap_region_t;
 
diff --git a/io/mmap.c b/io/mmap.c
index b0c1f764..04a828a4 100644
--- a/io/mmap.c
+++ b/io/mmap.c
@@ -42,7 +42,7 @@ print_mapping(
 	int		index,
 	int		braces)
 {
-	unsigned char	buffer[8] = { 0 };
+	char		buffer[8] = { 0 };
 	int		i;
 
 	static struct {
@@ -57,6 +57,10 @@ print_mapping(
 
 	for (i = 0, p = pflags; p->prot != PROT_NONE; i++, p++)
 		buffer[i] = (map->prot & p->prot) ? p->mode : '-';
+
+	if (map->map_sync)
+		sprintf(&buffer[i], " S");
+
 	printf("%c%03d%c 0x%lx - 0x%lx %s  %14s (%lld : %ld)\n",
 		braces? '[' : ' ', index, braces? ']' : ' ',
 		(unsigned long)map->addr,
@@ -147,6 +151,7 @@ mmap_help(void)
 " -r -- map with PROT_READ protection\n"
 " -w -- map with PROT_WRITE protection\n"
 " -x -- map with PROT_EXEC protection\n"
+" -S -- map with MAP_SYNC and MAP_SHARED_VALIDATE flags\n"
 " -s <size> -- first do mmap(size)/munmap(size), try to reserve some free space\n"
 " If no protection mode is specified, all are used by default.\n"
 "\n"));
@@ -162,7 +167,7 @@ mmap_f(
 	void		*address = NULL;
 	char		*filename;
 	size_t		blocksize, sectsize;
-	int		c, prot = 0;
+	int		c, prot = 0, flags = MAP_SHARED;
 
 	exitcode = 1;
 	if (argc == 1) {
@@ -186,7 +191,7 @@ mmap_f(
 
 	init_cvtnum(&blocksize, &sectsize);
 
-	while ((c = getopt(argc, argv, "rwxs:")) != EOF) {
+	while ((c = getopt(argc, argv, "rwxSs:")) != EOF) {
 		switch (c) {
 		case 'r':
 			prot |= PROT_READ;
@@ -197,6 +202,19 @@ mmap_f(
 		case 'x':
 			prot |= PROT_EXEC;
 			break;
+		case 'S':
+			flags = MAP_SYNC | MAP_SHARED_VALIDATE;
+
+			/*
+			 * If MAP_SYNC and MAP_SHARED_VALIDATE aren't defined
+			 * in the system headers we will have defined them
+			 * both as 0.
+			 */
+			if (!flags) {
+				printf("MAP_SYNC not supported\n");
+				return 0;
+			}
+			break;
 		case 's':
 			length2 = cvtnum(blocksize, sectsize, optarg);
 			break;
@@ -240,7 +258,7 @@ mmap_f(
 		               MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
 		munmap(address, length2);
 	}
-	address = mmap(address, length, prot, MAP_SHARED, file->fd, offset);
+	address = mmap(address, length, prot, flags, file->fd, offset);
 	if (address == MAP_FAILED) {
 		perror("mmap");
 		free(filename);
@@ -265,6 +283,7 @@ mmap_f(
 	mapping->offset = offset;
 	mapping->name = filename;
 	mapping->prot = prot;
+	mapping->map_sync = (flags == (MAP_SYNC | MAP_SHARED_VALIDATE));
 	exitcode = 0;
 	return 0;
 }
@@ -691,7 +710,7 @@ mmap_init(void)
 	mmap_cmd.argmax = -1;
 	mmap_cmd.flags = CMD_NOMAP_OK | CMD_NOFILE_OK |
 			 CMD_FOREIGN_OK | CMD_FLAG_ONESHOT;
-	mmap_cmd.args = _("[N] | [-rwx] [-s size] [off len]");
+	mmap_cmd.args = _("[N] | [-rwxS] [-s size] [off len]");
 	mmap_cmd.oneline =
 		_("mmap a range in the current file, show mappings");
 	mmap_cmd.help = mmap_help;
diff --git a/m4/package_libcdev.m4 b/m4/package_libcdev.m4
index 7b4dfc85..71cedc5c 100644
--- a/m4/package_libcdev.m4
+++ b/m4/package_libcdev.m4
@@ -328,3 +328,19 @@ AC_DEFUN([AC_HAVE_STATFS_FLAGS],
     )
     AC_SUBST(have_statfs_flags)
   ])
+
+#
+# Check if we have MAP_SYNC defines (Linux)
+#
+AC_DEFUN([AC_HAVE_MAP_SYNC],
+  [ AC_MSG_CHECKING([for MAP_SYNC])
+    AC_TRY_COMPILE([
+#include <asm-generic/mman.h>
+#include <asm-generic/mman-common.h>
+    ], [
+        int flags = MAP_SYNC | MAP_SHARED_VALIDATE;
+    ], have_map_sync=yes
+	AC_MSG_RESULT(yes),
+	AC_MSG_RESULT(no))
+    AC_SUBST(have_map_sync)
+  ])
diff --git a/man/man8/xfs_io.8 b/man/man8/xfs_io.8
index 9bf1a478..1693f7f1 100644
--- a/man/man8/xfs_io.8
+++ b/man/man8/xfs_io.8
@@ -764,7 +764,7 @@ Each (sec, nsec) pair constitutes a single timestamp value.
 
 .SH MEMORY MAPPED I/O COMMANDS
 .TP
-.BI "mmap [ " N " | [[ \-rwx ] [\-s " size " ] " "offset length " ]]
+.BI "mmap [ " N " | [[ \-rwxS ] [\-s " size " ] " "offset length " ]]
 With no arguments,
 .B mmap
 shows the current mappings. Specifying a single numeric argument
@@ -780,6 +780,10 @@ PROT_WRITE
 .RB ( \-w ),
 and PROT_EXEC
 .RB ( \-x ).
+The mapping will be created with the MAP_SHARED flag by default, or with the
+Linux specific (MAP_SYNC | MAP_SHARED_VALIDATE) flags if
+.B -S
+is given.
 .BI \-s " size"
 is used to do a mmap(size) && munmap(size) operation at first, try to reserve some
 extendible free memory space, if
-- 
2.14.3

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[xfsprogs PATCH v4 2/2] xfs_io: add a new 'log_writes' command

[Ross Zwisler]

Add a new 'log_writes' command to xfs_io so that we can add dm-log-writes
log marks.  It's helpful to allow users of xfs_io to adds these marks from
within xfs_io instead of waiting until after xfs_io exits because then they
are able to replay the dm-log-writes log up to immediately after another
xfs_io operation such as mwrite.  This isolates the log replay from other
operations that happen as part of xfs_io exiting (file handles being
closed, mmaps being torn down, etc.).  This also allows users to insert
multiple marks between different xfs_io commands.

Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Suggested-by: Dave Chinner <david@fromorbit.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
---
 configure.ac            |   1 +
 debian/control          |   2 +-
 include/builddefs.in    |   2 +
 io/Makefile             |   6 +++
 io/init.c               |   1 +
 io/io.h                 |   6 +++
 io/log_writes.c         | 106 ++++++++++++++++++++++++++++++++++++++++++++++++
 m4/Makefile             |   1 +
 m4/package_devmapper.m4 |  11 +++++
 man/man8/xfs_io.8       |  23 ++++++++++-
 10 files changed, 157 insertions(+), 2 deletions(-)
 create mode 100644 io/log_writes.c
 create mode 100644 m4/package_devmapper.m4

diff --git a/configure.ac b/configure.ac
index f3325aa0..f83d5817 100644
--- a/configure.ac
+++ b/configure.ac
@@ -164,6 +164,7 @@ AC_NEED_INTERNAL_FSXATTR
 AC_HAVE_GETFSMAP
 AC_HAVE_STATFS_FLAGS
 AC_HAVE_MAP_SYNC
+AC_HAVE_DEVMAPPER
 
 if test "$enable_blkid" = yes; then
 AC_HAVE_BLKID_TOPO
diff --git a/debian/control b/debian/control
index ad816622..5c26e3d7 100644
--- a/debian/control
+++ b/debian/control
@@ -3,7 +3,7 @@ Section: admin
 Priority: optional
 Maintainer: XFS Development Team <linux-xfs@vger.kernel.org>
 Uploaders: Nathan Scott <nathans@debian.org>, Anibal Monsalve Salazar <anibal@debian.org>
-Build-Depends: uuid-dev, dh-autoreconf, debhelper (>= 5), gettext, libtool, libreadline-gplv2-dev | libreadline5-dev, libblkid-dev (>= 2.17), linux-libc-dev
+Build-Depends: uuid-dev, dh-autoreconf, debhelper (>= 5), gettext, libtool, libreadline-gplv2-dev | libreadline5-dev, libblkid-dev (>= 2.17), linux-libc-dev, libdevmapper-dev
 Standards-Version: 3.9.1
 Homepage: http://xfs.org/
 
diff --git a/include/builddefs.in b/include/builddefs.in
index 126f7e95..66bdbfa2 100644
--- a/include/builddefs.in
+++ b/include/builddefs.in
@@ -35,6 +35,7 @@ LIBTERMCAP = @libtermcap@
 LIBEDITLINE = @libeditline@
 LIBREADLINE = @libreadline@
 LIBBLKID = @libblkid@
+LIBDEVMAPPER = @libdevmapper@
 LIBXFS = $(TOPDIR)/libxfs/libxfs.la
 LIBXCMD = $(TOPDIR)/libxcmd/libxcmd.la
 LIBXLOG = $(TOPDIR)/libxlog/libxlog.la
@@ -116,6 +117,7 @@ NEED_INTERNAL_FSXATTR = @need_internal_fsxattr@
 HAVE_GETFSMAP = @have_getfsmap@
 HAVE_STATFS_FLAGS = @have_statfs_flags@
 HAVE_MAP_SYNC = @have_map_sync@
+HAVE_DEVMAPPER = @have_devmapper@
 
 GCCFLAGS = -funsigned-char -fno-strict-aliasing -Wall
 #	   -Wbitwise -Wno-transparent-union -Wno-old-initializer -Wno-decl
diff --git a/io/Makefile b/io/Makefile
index 2987ee11..b7585a1b 100644
--- a/io/Makefile
+++ b/io/Makefile
@@ -107,6 +107,12 @@ ifeq ($(HAVE_MAP_SYNC),yes)
 LCFLAGS += -DHAVE_MAP_SYNC
 endif
 
+ifeq ($(HAVE_DEVMAPPER),yes)
+CFILES += log_writes.c
+LLDLIBS += $(LIBDEVMAPPER)
+LCFLAGS += -DHAVE_DEVMAPPER
+endif
+
 # On linux we get fsmap from the system or define it ourselves
 # so include this based on platform type.  If this reverts to only
 # the autoconf check w/o local definition, change to testing HAVE_GETFSMAP
diff --git a/io/init.c b/io/init.c
index 20d5f80d..34d87b5f 100644
--- a/io/init.c
+++ b/io/init.c
@@ -72,6 +72,7 @@ init_commands(void)
 	help_init();
 	imap_init();
 	inject_init();
+	log_writes_init();
 	madvise_init();
 	mincore_init();
 	mmap_init();
diff --git a/io/io.h b/io/io.h
index 8b2753b3..9349cc75 100644
--- a/io/io.h
+++ b/io/io.h
@@ -186,3 +186,9 @@ extern void		fsmap_init(void);
 #else
 # define fsmap_init()	do { } while (0)
 #endif
+
+#ifdef HAVE_DEVMAPPER
+extern void		log_writes_init(void);
+#else
+#define log_writes_init()	do { } while (0)
+#endif
diff --git a/io/log_writes.c b/io/log_writes.c
new file mode 100644
index 00000000..46ea1c26
--- /dev/null
+++ b/io/log_writes.c
@@ -0,0 +1,106 @@
+/*
+ * Copyright (c) 2017 Intel Corporation.
+ * All Rights Reserved.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it would be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write the Free Software Foundation,
+ * Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+ */
+
+#include "platform_defs.h"
+#include <libdevmapper.h>
+#include "command.h"
+#include "init.h"
+
+static cmdinfo_t log_writes_cmd;
+
+static int
+mark_log(const char *device, const char *mark)
+{
+	struct dm_task 	*dmt;
+	const int 	size = 80;
+	char 		message[size];
+	int 		len, ret = 0;
+
+	len = snprintf(message, size, "mark %s", mark);
+	if (len >= size) {
+		printf("mark '%s' is too long\n", mark);
+		return ret;
+	}
+
+	if (!(dmt = dm_task_create(DM_DEVICE_TARGET_MSG)))
+		return ret;
+
+	if (!dm_task_set_name(dmt, device))
+		goto out;
+
+	if (!dm_task_set_sector(dmt, 0))
+		goto out;
+
+	if (!dm_task_set_message(dmt, message))
+		goto out;
+
+	if (dm_task_run(dmt))
+		ret = 1;
+out:
+	dm_task_destroy(dmt);
+	return ret;
+}
+
+static int
+log_writes_f(
+	int			argc,
+	char			**argv)
+{
+	const char 	*device = NULL;
+	const char 	*mark = NULL;
+	int 		c;
+
+	exitcode = 1;
+	while ((c = getopt(argc, argv, "d:m:")) != EOF) {
+		switch (c) {
+		case 'd':
+			device = optarg;
+			break;
+		case 'm':
+			mark = optarg;
+			break;
+		default:
+			return command_usage(&log_writes_cmd);
+		}
+	}
+
+	if (device == NULL || mark == NULL)
+		return command_usage(&log_writes_cmd);
+
+	if (mark_log(device, mark))
+		exitcode = 0;
+
+	return 0;
+}
+
+void
+log_writes_init(void)
+{
+	log_writes_cmd.name = "log_writes";
+	log_writes_cmd.altname = "lw";
+	log_writes_cmd.cfunc = log_writes_f;
+	log_writes_cmd.flags = CMD_NOMAP_OK | CMD_NOFILE_OK | CMD_FOREIGN_OK
+				| CMD_FLAG_ONESHOT;
+	log_writes_cmd.argmin = 0;
+	log_writes_cmd.argmax = -1;
+	log_writes_cmd.args = _("-d device -m mark");
+	log_writes_cmd.oneline =
+		_("create mark <mark> in the dm-log-writes log specified by <device>");
+
+	add_command(&log_writes_cmd);
+}
diff --git a/m4/Makefile b/m4/Makefile
index 4706121b..77f2edda 100644
--- a/m4/Makefile
+++ b/m4/Makefile
@@ -15,6 +15,7 @@ CONFIGURE = \
 LSRCFILES = \
 	manual_format.m4 \
 	package_blkid.m4 \
+	package_devmapper.m4 \
 	package_globals.m4 \
 	package_libcdev.m4 \
 	package_pthread.m4 \
diff --git a/m4/package_devmapper.m4 b/m4/package_devmapper.m4
new file mode 100644
index 00000000..821f283c
--- /dev/null
+++ b/m4/package_devmapper.m4
@@ -0,0 +1,11 @@
+#
+# See if libdevmapper is available on the system.
+#
+AC_DEFUN([AC_HAVE_DEVMAPPER],
+[ AC_SEARCH_LIBS([dm_task_create], [devmapper],
+        libdevmapper="-ldevmapper"
+        have_devmapper=yes,
+        have_devmapper=no,)
+    AC_SUBST(have_devmapper)
+    AC_SUBST(libdevmapper)
+])
diff --git a/man/man8/xfs_io.8 b/man/man8/xfs_io.8
index 1693f7f1..4fce6d39 100644
--- a/man/man8/xfs_io.8
+++ b/man/man8/xfs_io.8
@@ -1123,7 +1123,27 @@ version of policy structure (numeric)
 .BR get_encpolicy
 On filesystems that support encryption, display the encryption policy of the
 current file.
+.RE
+.PD
+.TP
+.BI "log_writes \-d " device " \-m "  mark
+Create a mark named
+.I mark
+in the dm-log-writes log specified by
+.I device.
+This is intended to be equivalent to the shell command:
 
+.B dmsetup message
+.I device
+.B 0 mark
+.I mark
+.PD
+.RE
+.TP
+.B lw
+See the
+.B log_writes
+command.
 .SH SEE ALSO
 .BR mkfs.xfs (8),
 .BR xfsctl (3),
@@ -1141,4 +1161,5 @@ current file.
 .BR open (2),
 .BR pread (2),
 .BR pwrite (2),
-.BR readdir (3).
+.BR readdir (3),
+.BR dmsetup (8).
-- 
2.14.3

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Re: [xfsprogs PATCH v4 1/2] xfs_io: add MAP_SYNC support to mmap()

[Darrick J. Wong]

On Thu, Dec 21, 2017 at 03:07:59PM -0700, Ross Zwisler wrote:
> Add support for a new -S flag to xfs_io's mmap command.  This opens the
> mapping with the (MAP_SYNC | MAP_SHARED_VALIDATE) flags instead of the
> standard MAP_SHARED flag.
> 
> Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
> Suggested-by: Dave Chinner <david@fromorbit.com>

Looks ok,
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>

> ---
>  configure.ac          |  1 +
>  include/builddefs.in  |  1 +
>  include/linux.h       |  8 ++++++++
>  io/Makefile           |  4 ++++
>  io/io.h               |  1 +
>  io/mmap.c             | 29 ++++++++++++++++++++++++-----
>  m4/package_libcdev.m4 | 16 ++++++++++++++++
>  man/man8/xfs_io.8     |  6 +++++-
>  8 files changed, 60 insertions(+), 6 deletions(-)
> 
> diff --git a/configure.ac b/configure.ac
> index e5d0309f..f3325aa0 100644
> --- a/configure.ac
> +++ b/configure.ac
> @@ -163,6 +163,7 @@ AC_HAVE_MREMAP
>  AC_NEED_INTERNAL_FSXATTR
>  AC_HAVE_GETFSMAP
>  AC_HAVE_STATFS_FLAGS
> +AC_HAVE_MAP_SYNC
>  
>  if test "$enable_blkid" = yes; then
>  AC_HAVE_BLKID_TOPO
> diff --git a/include/builddefs.in b/include/builddefs.in
> index fd274ddc..126f7e95 100644
> --- a/include/builddefs.in
> +++ b/include/builddefs.in
> @@ -115,6 +115,7 @@ HAVE_MREMAP = @have_mremap@
>  NEED_INTERNAL_FSXATTR = @need_internal_fsxattr@
>  HAVE_GETFSMAP = @have_getfsmap@
>  HAVE_STATFS_FLAGS = @have_statfs_flags@
> +HAVE_MAP_SYNC = @have_map_sync@
>  
>  GCCFLAGS = -funsigned-char -fno-strict-aliasing -Wall
>  #	   -Wbitwise -Wno-transparent-union -Wno-old-initializer -Wno-decl
> diff --git a/include/linux.h b/include/linux.h
> index 6ce344c5..1998941a 100644
> --- a/include/linux.h
> +++ b/include/linux.h
> @@ -327,4 +327,12 @@ fsmap_advance(
>  #define HAVE_GETFSMAP
>  #endif /* HAVE_GETFSMAP */
>  
> +#ifndef HAVE_MAP_SYNC
> +#define MAP_SYNC 0
> +#define MAP_SHARED_VALIDATE 0
> +#else
> +#include <asm-generic/mman.h>
> +#include <asm-generic/mman-common.h>
> +#endif /* HAVE_MAP_SYNC */
> +
>  #endif	/* __XFS_LINUX_H__ */
> diff --git a/io/Makefile b/io/Makefile
> index 6725936d..2987ee11 100644
> --- a/io/Makefile
> +++ b/io/Makefile
> @@ -103,6 +103,10 @@ ifeq ($(HAVE_MREMAP),yes)
>  LCFLAGS += -DHAVE_MREMAP
>  endif
>  
> +ifeq ($(HAVE_MAP_SYNC),yes)
> +LCFLAGS += -DHAVE_MAP_SYNC
> +endif
> +
>  # On linux we get fsmap from the system or define it ourselves
>  # so include this based on platform type.  If this reverts to only
>  # the autoconf check w/o local definition, change to testing HAVE_GETFSMAP
> diff --git a/io/io.h b/io/io.h
> index 3862985f..8b2753b3 100644
> --- a/io/io.h
> +++ b/io/io.h
> @@ -65,6 +65,7 @@ typedef struct mmap_region {
>  	size_t		length;		/* length of mapping */
>  	off64_t		offset;		/* start offset into backing file */
>  	int		prot;		/* protection mode of the mapping */
> +	bool		map_sync;	/* is this a MAP_SYNC mapping? */
>  	char		*name;		/* name of backing file */
>  } mmap_region_t;
>  
> diff --git a/io/mmap.c b/io/mmap.c
> index b0c1f764..04a828a4 100644
> --- a/io/mmap.c
> +++ b/io/mmap.c
> @@ -42,7 +42,7 @@ print_mapping(
>  	int		index,
>  	int		braces)
>  {
> -	unsigned char	buffer[8] = { 0 };
> +	char		buffer[8] = { 0 };
>  	int		i;
>  
>  	static struct {
> @@ -57,6 +57,10 @@ print_mapping(
>  
>  	for (i = 0, p = pflags; p->prot != PROT_NONE; i++, p++)
>  		buffer[i] = (map->prot & p->prot) ? p->mode : '-';
> +
> +	if (map->map_sync)
> +		sprintf(&buffer[i], " S");
> +
>  	printf("%c%03d%c 0x%lx - 0x%lx %s  %14s (%lld : %ld)\n",
>  		braces? '[' : ' ', index, braces? ']' : ' ',
>  		(unsigned long)map->addr,
> @@ -147,6 +151,7 @@ mmap_help(void)
>  " -r -- map with PROT_READ protection\n"
>  " -w -- map with PROT_WRITE protection\n"
>  " -x -- map with PROT_EXEC protection\n"
> +" -S -- map with MAP_SYNC and MAP_SHARED_VALIDATE flags\n"
>  " -s <size> -- first do mmap(size)/munmap(size), try to reserve some free space\n"
>  " If no protection mode is specified, all are used by default.\n"
>  "\n"));
> @@ -162,7 +167,7 @@ mmap_f(
>  	void		*address = NULL;
>  	char		*filename;
>  	size_t		blocksize, sectsize;
> -	int		c, prot = 0;
> +	int		c, prot = 0, flags = MAP_SHARED;
>  
>  	exitcode = 1;
>  	if (argc == 1) {
> @@ -186,7 +191,7 @@ mmap_f(
>  
>  	init_cvtnum(&blocksize, &sectsize);
>  
> -	while ((c = getopt(argc, argv, "rwxs:")) != EOF) {
> +	while ((c = getopt(argc, argv, "rwxSs:")) != EOF) {
>  		switch (c) {
>  		case 'r':
>  			prot |= PROT_READ;
> @@ -197,6 +202,19 @@ mmap_f(
>  		case 'x':
>  			prot |= PROT_EXEC;
>  			break;
> +		case 'S':
> +			flags = MAP_SYNC | MAP_SHARED_VALIDATE;
> +
> +			/*
> +			 * If MAP_SYNC and MAP_SHARED_VALIDATE aren't defined
> +			 * in the system headers we will have defined them
> +			 * both as 0.
> +			 */
> +			if (!flags) {
> +				printf("MAP_SYNC not supported\n");
> +				return 0;
> +			}
> +			break;
>  		case 's':
>  			length2 = cvtnum(blocksize, sectsize, optarg);
>  			break;
> @@ -240,7 +258,7 @@ mmap_f(
>  		               MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
>  		munmap(address, length2);
>  	}
> -	address = mmap(address, length, prot, MAP_SHARED, file->fd, offset);
> +	address = mmap(address, length, prot, flags, file->fd, offset);
>  	if (address == MAP_FAILED) {
>  		perror("mmap");
>  		free(filename);
> @@ -265,6 +283,7 @@ mmap_f(
>  	mapping->offset = offset;
>  	mapping->name = filename;
>  	mapping->prot = prot;
> +	mapping->map_sync = (flags == (MAP_SYNC | MAP_SHARED_VALIDATE));
>  	exitcode = 0;
>  	return 0;
>  }
> @@ -691,7 +710,7 @@ mmap_init(void)
>  	mmap_cmd.argmax = -1;
>  	mmap_cmd.flags = CMD_NOMAP_OK | CMD_NOFILE_OK |
>  			 CMD_FOREIGN_OK | CMD_FLAG_ONESHOT;
> -	mmap_cmd.args = _("[N] | [-rwx] [-s size] [off len]");
> +	mmap_cmd.args = _("[N] | [-rwxS] [-s size] [off len]");
>  	mmap_cmd.oneline =
>  		_("mmap a range in the current file, show mappings");
>  	mmap_cmd.help = mmap_help;
> diff --git a/m4/package_libcdev.m4 b/m4/package_libcdev.m4
> index 7b4dfc85..71cedc5c 100644
> --- a/m4/package_libcdev.m4
> +++ b/m4/package_libcdev.m4
> @@ -328,3 +328,19 @@ AC_DEFUN([AC_HAVE_STATFS_FLAGS],
>      )
>      AC_SUBST(have_statfs_flags)
>    ])
> +
> +#
> +# Check if we have MAP_SYNC defines (Linux)
> +#
> +AC_DEFUN([AC_HAVE_MAP_SYNC],
> +  [ AC_MSG_CHECKING([for MAP_SYNC])
> +    AC_TRY_COMPILE([
> +#include <asm-generic/mman.h>
> +#include <asm-generic/mman-common.h>
> +    ], [
> +        int flags = MAP_SYNC | MAP_SHARED_VALIDATE;
> +    ], have_map_sync=yes
> +	AC_MSG_RESULT(yes),
> +	AC_MSG_RESULT(no))
> +    AC_SUBST(have_map_sync)
> +  ])
> diff --git a/man/man8/xfs_io.8 b/man/man8/xfs_io.8
> index 9bf1a478..1693f7f1 100644
> --- a/man/man8/xfs_io.8
> +++ b/man/man8/xfs_io.8
> @@ -764,7 +764,7 @@ Each (sec, nsec) pair constitutes a single timestamp value.
>  
>  .SH MEMORY MAPPED I/O COMMANDS
>  .TP
> -.BI "mmap [ " N " | [[ \-rwx ] [\-s " size " ] " "offset length " ]]
> +.BI "mmap [ " N " | [[ \-rwxS ] [\-s " size " ] " "offset length " ]]
>  With no arguments,
>  .B mmap
>  shows the current mappings. Specifying a single numeric argument
> @@ -780,6 +780,10 @@ PROT_WRITE
>  .RB ( \-w ),
>  and PROT_EXEC
>  .RB ( \-x ).
> +The mapping will be created with the MAP_SHARED flag by default, or with the
> +Linux specific (MAP_SYNC | MAP_SHARED_VALIDATE) flags if
> +.B -S
> +is given.
>  .BI \-s " size"
>  is used to do a mmap(size) && munmap(size) operation at first, try to reserve some
>  extendible free memory space, if
> -- 
> 2.14.3
> 
> --
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