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

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

[Ross Zwisler]

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.

You can find an xfsprogs branch with this series here:

https://git.kernel.org/pub/scm/linux/kernel/git/zwisler/xfsprogs-dev.git/log/?h=map_sync

Both MAP_SYNC and the DAX enhancements for dm-log-writes will be found in
the upcoming v4.15-rc1.  For ease of testing I've posted a kernel that is
v4.14 plus just those two patch series here:

https://git.kernel.org/pub/scm/linux/kernel/git/zwisler/linux.git/log/?h=map_sync_dm_log_writes

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

 configure.ac          |  1 +
 include/builddefs.in  |  1 +
 include/linux.h       |  5 ++++
 io/Makefile           |  5 ++--
 io/init.c             |  1 +
 io/io.h               |  2 ++
 io/log_writes.c       | 78 +++++++++++++++++++++++++++++++++++++++++++++++++++
 io/mmap.c             | 19 +++++++++----
 m4/package_libcdev.m4 | 16 +++++++++++
 man/man8/xfs_io.8     | 25 ++++++++++++++++-
 10 files changed, 145 insertions(+), 8 deletions(-)
 create mode 100644 io/log_writes.c

--
2.9.5

[xfsprogs PATCH 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       |  5 +++++
 io/io.h               |  1 +
 io/mmap.c             | 19 ++++++++++++++-----
 m4/package_libcdev.m4 | 16 ++++++++++++++++
 man/man8/xfs_io.8     |  6 +++++-
 7 files changed, 43 insertions(+), 6 deletions(-)

diff --git a/configure.ac b/configure.ac
index cb23fb8..7153c9f 100644
--- a/configure.ac
+++ b/configure.ac
@@ -162,6 +162,7 @@ AC_HAVE_FSETXATTR
 AC_HAVE_MREMAP
 AC_NEED_INTERNAL_FSXATTR
 AC_HAVE_GETFSMAP
+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 1d454b6..78b71fe 100644
--- a/include/builddefs.in
+++ b/include/builddefs.in
@@ -114,6 +114,7 @@ HAVE_FSETXATTR = @have_fsetxattr@
 HAVE_MREMAP = @have_mremap@
 NEED_INTERNAL_FSXATTR = @need_internal_fsxattr@
 HAVE_GETFSMAP = @have_getfsmap@
+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 6ce344c..4ee03ed 100644
--- a/include/linux.h
+++ b/include/linux.h
@@ -327,4 +327,9 @@ fsmap_advance(
 #define HAVE_GETFSMAP
 #endif /* HAVE_GETFSMAP */
 
+#ifndef HAVE_MAP_SYNC
+#define MAP_SYNC 0x80000
+#define MAP_SHARED_VALIDATE 0x3
+#endif /* HAVE_MAP_SYNC */
+
 #endif	/* __XFS_LINUX_H__ */
diff --git a/io/io.h b/io/io.h
index 3862985..8b2753b 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 7a8150e..520b037 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,
@@ -146,6 +150,7 @@ 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_SHARED_VALIDATE and MAP_SYNC 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"));
@@ -161,7 +166,7 @@ mmap_f(
 	void		*address = NULL;
 	char		*filename;
 	size_t		blocksize, sectsize;
-	int		c, prot = 0;
+	int		c, prot = 0, flags = MAP_SHARED;
 
 	if (argc == 1) {
 		if (mapping)
@@ -184,7 +189,7 @@ 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;
@@ -195,6 +200,9 @@ mmap_f(
 		case 'x':
 			prot |= PROT_EXEC;
 			break;
+		case 'S':
+			flags = MAP_SHARED_VALIDATE | MAP_SYNC;
+			break;
 		case 's':
 			length2 = cvtnum(blocksize, sectsize, optarg);
 			break;
@@ -238,7 +246,7 @@ 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);
@@ -263,6 +271,7 @@ mmap_f(
 	mapping->offset = offset;
 	mapping->name = filename;
 	mapping->prot = prot;
+	mapping->map_sync = (flags == (MAP_SHARED_VALIDATE | MAP_SYNC));
 	return 0;
 }
 
@@ -676,7 +685,7 @@ 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 fdf9d69..598f5df 100644
--- a/m4/package_libcdev.m4
+++ b/m4/package_libcdev.m4
@@ -314,3 +314,19 @@ AC_DEFUN([AC_HAVE_GETFSMAP],
        AC_MSG_RESULT(no))
     AC_SUBST(have_getfsmap)
   ])
+
+#
+# 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_SHARED_VALIDATE | MAP_SYNC;
+    ], 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 9bf1a47..1693f7f 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
-- 
2.9.5

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

[Dan Williams]

On Fri, Nov 17, 2017 at 12:25 PM, Ross Zwisler
<ross.zwisler@linux.intel.com> 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>
> ---
>  configure.ac          |  1 +
>  include/builddefs.in  |  1 +
>  include/linux.h       |  5 +++++
>  io/io.h               |  1 +
>  io/mmap.c             | 19 ++++++++++++++-----
>  m4/package_libcdev.m4 | 16 ++++++++++++++++
>  man/man8/xfs_io.8     |  6 +++++-
>  7 files changed, 43 insertions(+), 6 deletions(-)
>
> diff --git a/configure.ac b/configure.ac
> index cb23fb8..7153c9f 100644
> --- a/configure.ac
> +++ b/configure.ac
> @@ -162,6 +162,7 @@ AC_HAVE_FSETXATTR
>  AC_HAVE_MREMAP
>  AC_NEED_INTERNAL_FSXATTR
>  AC_HAVE_GETFSMAP
> +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 1d454b6..78b71fe 100644
> --- a/include/builddefs.in
> +++ b/include/builddefs.in
> @@ -114,6 +114,7 @@ HAVE_FSETXATTR = @have_fsetxattr@
>  HAVE_MREMAP = @have_mremap@
>  NEED_INTERNAL_FSXATTR = @need_internal_fsxattr@
>  HAVE_GETFSMAP = @have_getfsmap@
> +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 6ce344c..4ee03ed 100644
> --- a/include/linux.h
> +++ b/include/linux.h
> @@ -327,4 +327,9 @@ fsmap_advance(
>  #define HAVE_GETFSMAP
>  #endif /* HAVE_GETFSMAP */
>
> +#ifndef HAVE_MAP_SYNC
> +#define MAP_SYNC 0x80000

Hmm, this is the x86 specific value of MAP_SYNC. I think it would be
better to define MAP_SYNC to zero in this case and check for MAP_SYNC
== 0 at run time.

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

[Ross Zwisler]

On Fri, Nov 17, 2017 at 12:35:43PM -0800, Dan Williams wrote:
> On Fri, Nov 17, 2017 at 12:25 PM, Ross Zwisler
> <ross.zwisler@linux.intel.com> 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>
> > ---
> >  configure.ac          |  1 +
> >  include/builddefs.in  |  1 +
> >  include/linux.h       |  5 +++++
> >  io/io.h               |  1 +
> >  io/mmap.c             | 19 ++++++++++++++-----
> >  m4/package_libcdev.m4 | 16 ++++++++++++++++
> >  man/man8/xfs_io.8     |  6 +++++-
> >  7 files changed, 43 insertions(+), 6 deletions(-)
> >
> > diff --git a/configure.ac b/configure.ac
> > index cb23fb8..7153c9f 100644
> > --- a/configure.ac
> > +++ b/configure.ac
> > @@ -162,6 +162,7 @@ AC_HAVE_FSETXATTR
> >  AC_HAVE_MREMAP
> >  AC_NEED_INTERNAL_FSXATTR
> >  AC_HAVE_GETFSMAP
> > +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 1d454b6..78b71fe 100644
> > --- a/include/builddefs.in
> > +++ b/include/builddefs.in
> > @@ -114,6 +114,7 @@ HAVE_FSETXATTR = @have_fsetxattr@
> >  HAVE_MREMAP = @have_mremap@
> >  NEED_INTERNAL_FSXATTR = @need_internal_fsxattr@
> >  HAVE_GETFSMAP = @have_getfsmap@
> > +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 6ce344c..4ee03ed 100644
> > --- a/include/linux.h
> > +++ b/include/linux.h
> > @@ -327,4 +327,9 @@ fsmap_advance(
> >  #define HAVE_GETFSMAP
> >  #endif /* HAVE_GETFSMAP */
> >
> > +#ifndef HAVE_MAP_SYNC
> > +#define MAP_SYNC 0x80000
> 
> Hmm, this is the x86 specific value of MAP_SYNC. I think it would be
> better to define MAP_SYNC to zero in this case and check for MAP_SYNC
> == 0 at run time.

Ah, so instead of defining MAP_SYNC if the proper headers aren't installed,
set to 0 and disallow the -S option?  Fair enough.

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

[Darrick J. Wong]

On Fri, Nov 17, 2017 at 01:25:23PM -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>
> ---
>  configure.ac          |  1 +
>  include/builddefs.in  |  1 +
>  include/linux.h       |  5 +++++
>  io/io.h               |  1 +
>  io/mmap.c             | 19 ++++++++++++++-----
>  m4/package_libcdev.m4 | 16 ++++++++++++++++
>  man/man8/xfs_io.8     |  6 +++++-
>  7 files changed, 43 insertions(+), 6 deletions(-)
> 
> diff --git a/configure.ac b/configure.ac
> index cb23fb8..7153c9f 100644
> --- a/configure.ac
> +++ b/configure.ac
> @@ -162,6 +162,7 @@ AC_HAVE_FSETXATTR
>  AC_HAVE_MREMAP
>  AC_NEED_INTERNAL_FSXATTR
>  AC_HAVE_GETFSMAP
> +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 1d454b6..78b71fe 100644
> --- a/include/builddefs.in
> +++ b/include/builddefs.in
> @@ -114,6 +114,7 @@ HAVE_FSETXATTR = @have_fsetxattr@
>  HAVE_MREMAP = @have_mremap@
>  NEED_INTERNAL_FSXATTR = @need_internal_fsxattr@
>  HAVE_GETFSMAP = @have_getfsmap@
> +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 6ce344c..4ee03ed 100644
> --- a/include/linux.h
> +++ b/include/linux.h
> @@ -327,4 +327,9 @@ fsmap_advance(
>  #define HAVE_GETFSMAP
>  #endif /* HAVE_GETFSMAP */
>  
> +#ifndef HAVE_MAP_SYNC
> +#define MAP_SYNC 0x80000
> +#define MAP_SHARED_VALIDATE 0x3
> +#endif /* HAVE_MAP_SYNC */

Hmm, what's the point of ifndef/define if you have an configure.ac check?

> +
>  #endif	/* __XFS_LINUX_H__ */
> diff --git a/io/io.h b/io/io.h
> index 3862985..8b2753b 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 7a8150e..520b037 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");

Does buffer need enlarging here?

> +
>  	printf("%c%03d%c 0x%lx - 0x%lx %s  %14s (%lld : %ld)\n",
>  		braces? '[' : ' ', index, braces? ']' : ' ',
>  		(unsigned long)map->addr,
> @@ -146,6 +150,7 @@ 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_SHARED_VALIDATE and MAP_SYNC 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"));
> @@ -161,7 +166,7 @@ mmap_f(
>  	void		*address = NULL;
>  	char		*filename;
>  	size_t		blocksize, sectsize;
> -	int		c, prot = 0;
> +	int		c, prot = 0, flags = MAP_SHARED;
>  
>  	if (argc == 1) {
>  		if (mapping)
> @@ -184,7 +189,7 @@ 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;
> @@ -195,6 +200,9 @@ mmap_f(
>  		case 'x':
>  			prot |= PROT_EXEC;
>  			break;
> +		case 'S':
> +			flags = MAP_SHARED_VALIDATE | MAP_SYNC;
> +			break;
>  		case 's':
>  			length2 = cvtnum(blocksize, sectsize, optarg);
>  			break;
> @@ -238,7 +246,7 @@ 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);
> @@ -263,6 +271,7 @@ mmap_f(
>  	mapping->offset = offset;
>  	mapping->name = filename;
>  	mapping->prot = prot;
> +	mapping->map_sync = (flags == (MAP_SHARED_VALIDATE | MAP_SYNC));
>  	return 0;
>  }
>  
> @@ -676,7 +685,7 @@ 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 fdf9d69..598f5df 100644
> --- a/m4/package_libcdev.m4
> +++ b/m4/package_libcdev.m4
> @@ -314,3 +314,19 @@ AC_DEFUN([AC_HAVE_GETFSMAP],
>         AC_MSG_RESULT(no))
>      AC_SUBST(have_getfsmap)
>    ])
> +
> +#
> +# 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_SHARED_VALIDATE | MAP_SYNC;
> +    ], 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 9bf1a47..1693f7f 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.

Woo, documentation!

--D

>  .BI \-s " size"
>  is used to do a mmap(size) && munmap(size) operation at first, try to reserve some
>  extendible free memory space, if
> -- 
> 2.9.5
> 
> --
> To unsubscribe from this list: send the line "unsubscribe linux-xfs" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

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

[Ross Zwisler]

On Fri, Nov 17, 2017 at 12:40:21PM -0800, Darrick J. Wong wrote:
> On Fri, Nov 17, 2017 at 01:25:23PM -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>
> > ---
<>
> > diff --git a/include/linux.h b/include/linux.h
> > index 6ce344c..4ee03ed 100644
> > --- a/include/linux.h
> > +++ b/include/linux.h
> > @@ -327,4 +327,9 @@ fsmap_advance(
> >  #define HAVE_GETFSMAP
> >  #endif /* HAVE_GETFSMAP */
> >  
> > +#ifndef HAVE_MAP_SYNC
> > +#define MAP_SYNC 0x80000
> > +#define MAP_SHARED_VALIDATE 0x3
> > +#endif /* HAVE_MAP_SYNC */
> 
> Hmm, what's the point of ifndef/define if you have an configure.ac check?

I'm following the example of HAVE_GETFSMAP.  It does a check to see if the
headers have proper support in m4/package_libcdev.m4, then has code in this
file to provide defines if they aren't provided in the system.

> > diff --git a/io/mmap.c b/io/mmap.c
> > index 7a8150e..520b037 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");
> 
> Does buffer need enlarging here?

Nope.  The buffer is 8 chars, and the 'rwx\0' string only uses 4.
"rwx S\0" uses 6, so we're still good to go.

[xfsprogs PATCH 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 via the external 'dmsetup' executable.  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>
---
 io/Makefile       |  5 ++--
 io/init.c         |  1 +
 io/io.h           |  1 +
 io/log_writes.c   | 78 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 man/man8/xfs_io.8 | 19 ++++++++++++++
 5 files changed, 102 insertions(+), 2 deletions(-)
 create mode 100644 io/log_writes.c

diff --git a/io/Makefile b/io/Makefile
index 050d6bd..51b2eae 100644
--- a/io/Makefile
+++ b/io/Makefile
@@ -10,8 +10,9 @@ LSRCFILES = xfs_bmap.sh xfs_freeze.sh xfs_mkfile.sh
 HFILES = init.h io.h
 CFILES = init.c \
 	attr.c bmap.c cowextsize.c encrypt.c file.c freeze.c fsync.c \
-	getrusage.c imap.c link.c mmap.c open.c parent.c pread.c prealloc.c \
-	pwrite.c reflink.c seek.c shutdown.c stat.c sync.c truncate.c utimes.c
+	getrusage.c imap.c link.c log_writes.c mmap.c open.c parent.c pread.c \
+	prealloc.c pwrite.c reflink.c seek.c shutdown.c stat.c sync.c \
+	truncate.c utimes.c
 
 LLDLIBS = $(LIBXCMD) $(LIBHANDLE) $(LIBPTHREAD)
 LTDEPENDENCIES = $(LIBXCMD) $(LIBHANDLE)
diff --git a/io/init.c b/io/init.c
index 20d5f80..34d87b5 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 8b2753b..d62034a 100644
--- a/io/io.h
+++ b/io/io.h
@@ -109,6 +109,7 @@ extern void		getrusage_init(void);
 extern void		help_init(void);
 extern void		imap_init(void);
 extern void		inject_init(void);
+extern void		log_writes_init(void);
 extern void		mmap_init(void);
 extern void		open_init(void);
 extern void		parent_init(void);
diff --git a/io/log_writes.c b/io/log_writes.c
new file mode 100644
index 0000000..bc3952c
--- /dev/null
+++ b/io/log_writes.c
@@ -0,0 +1,78 @@
+/*
+ * 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 "command.h"
+#include "init.h"
+
+static cmdinfo_t log_writes_cmd;
+
+static int
+mark_log(char *device, char *mark)
+{
+	char command[256];
+
+	snprintf(command, 256, "dmsetup message %s 0 mark %s",
+			device, mark);
+
+	return system(command);
+}
+
+static int
+log_writes_f(
+	int			argc,
+	char			**argv)
+{
+	char *device = NULL;
+	char *mark = NULL;
+	int c;
+
+	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);
+
+	return mark_log(device, mark);
+}
+
+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;
+	log_writes_cmd.argmin = 0;
+	log_writes_cmd.argmax = -1;
+	log_writes_cmd.args = _("-d device -m mark");
+	log_writes_cmd.oneline =
+		_("uses dmsetup to interact with the dm-log-writes module");
+
+	add_command(&log_writes_cmd);
+}
diff --git a/man/man8/xfs_io.8 b/man/man8/xfs_io.8
index 1693f7f..f18af99 100644
--- a/man/man8/xfs_io.8
+++ b/man/man8/xfs_io.8
@@ -1123,7 +1123,25 @@ 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
+Use
+.B dmsetup
+to interact with the
+.B dm-log-writes
+kernel module.  Currently the only operation
+supported is the creation of a mark in the log by executing the shell command:
 
+.B dmsetup message <device> 0 mark <mark>
+.PD
+.RE
+.TP
+.B lw
+See the
+.B log_writes
+command.
 .SH SEE ALSO
 .BR mkfs.xfs (8),
 .BR xfsctl (3),
@@ -1142,3 +1160,4 @@ current file.
 .BR pread (2),
 .BR pwrite (2),
 .BR readdir (3).
+.BR dmsetup (8).
-- 
2.9.5

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

[Eric Sandeen]

On 11/17/17 2:25 PM, Ross Zwisler wrote:
> Add a new 'log_writes' command to xfs_io so that we can add dm-log-writes
> log marks via the external 'dmsetup' executable.  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>

Without reviewing in detail, what is the advantage of wrapping dmsetup
into xfs_io?  My first inclination is that there is none at all, and
xfstests can call dmsetup as easily as they can call xfs_io.  No?

-Eric

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

[Ross Zwisler]

On Fri, Nov 17, 2017 at 02:39:07PM -0600, Eric Sandeen wrote:
> On 11/17/17 2:25 PM, Ross Zwisler wrote:
> > Add a new 'log_writes' command to xfs_io so that we can add dm-log-writes
> > log marks via the external 'dmsetup' executable.  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>
> 
> Without reviewing in detail, what is the advantage of wrapping dmsetup
> into xfs_io?  My first inclination is that there is none at all, and
> xfstests can call dmsetup as easily as they can call xfs_io.  No?
> 
> -Eric

I commented on this a bit in the changelog for the 2nd patch:

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.

I agree that the shell-out to dmsetup isn't awesome...  For the current test I
have written I think we can get away with just assuming that the xfs_io exit
stuff won't interact too heavily with the dm-log-writes log, and we could
potentially move the dmsetup call back into the fstest.  This is how I
initially had it, and moved it into the C program via shell-out in response to
Amir's feedback:

https://lists.01.org/pipermail/linux-nvdimm/2017-October/012976.html

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

[Eric Sandeen]

On 11/17/17 2:48 PM, Ross Zwisler wrote:
> On Fri, Nov 17, 2017 at 02:39:07PM -0600, Eric Sandeen wrote:
>> On 11/17/17 2:25 PM, Ross Zwisler wrote:
>>> Add a new 'log_writes' command to xfs_io so that we can add dm-log-writes
>>> log marks via the external 'dmsetup' executable.  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>
>>
>> Without reviewing in detail, what is the advantage of wrapping dmsetup
>> into xfs_io?  My first inclination is that there is none at all, and
>> xfstests can call dmsetup as easily as they can call xfs_io.  No?
>>
>> -Eric
> 
> I commented on this a bit in the changelog for the 2nd patch:
> 
> 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.
> 
> I agree that the shell-out to dmsetup isn't awesome...  For the current test I
> have written I think we can get away with just assuming that the xfs_io exit
> stuff won't interact too heavily with the dm-log-writes log, and we could
> potentially move the dmsetup call back into the fstest.  This is how I
> initially had it, and moved it into the C program via shell-out in response to
> Amir's feedback:

Sorry, terrible of me to not have read that.  :(  Ok, so next question - 
DM_TARGET_MSG seems to be public, can we just invoke the ioctl directly
instead of shelling out to dmsetup?

I'm checking w/ the dm folks too, to make sure that's expected to work.  As
long as the use isn't too tricky it seems like that might be better.

-Eric

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

[Ross Zwisler]

On Fri, Nov 17, 2017 at 03:03:39PM -0600, Eric Sandeen wrote:
> On 11/17/17 2:48 PM, Ross Zwisler wrote:
> > On Fri, Nov 17, 2017 at 02:39:07PM -0600, Eric Sandeen wrote:
> >> On 11/17/17 2:25 PM, Ross Zwisler wrote:
> >>> Add a new 'log_writes' command to xfs_io so that we can add dm-log-writes
> >>> log marks via the external 'dmsetup' executable.  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>
> >>
> >> Without reviewing in detail, what is the advantage of wrapping dmsetup
> >> into xfs_io?  My first inclination is that there is none at all, and
> >> xfstests can call dmsetup as easily as they can call xfs_io.  No?
> >>
> >> -Eric
> > 
> > I commented on this a bit in the changelog for the 2nd patch:
> > 
> > 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.
> > 
> > I agree that the shell-out to dmsetup isn't awesome...  For the current test I
> > have written I think we can get away with just assuming that the xfs_io exit
> > stuff won't interact too heavily with the dm-log-writes log, and we could
> > potentially move the dmsetup call back into the fstest.  This is how I
> > initially had it, and moved it into the C program via shell-out in response to
> > Amir's feedback:
> 
> Sorry, terrible of me to not have read that.  :(  Ok, so next question - 
> DM_TARGET_MSG seems to be public, can we just invoke the ioctl directly
> instead of shelling out to dmsetup?
> 
> I'm checking w/ the dm folks too, to make sure that's expected to work.  As
> long as the use isn't too tricky it seems like that might be better.

Yea, that seems like a better option - I'll take a look.  Thanks for the
suggestion.

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

[Eric Sandeen]

On 11/17/17 3:14 PM, Ross Zwisler wrote:
> On Fri, Nov 17, 2017 at 03:03:39PM -0600, Eric Sandeen wrote:
>> On 11/17/17 2:48 PM, Ross Zwisler wrote:
>>> On Fri, Nov 17, 2017 at 02:39:07PM -0600, Eric Sandeen wrote:
>>>> On 11/17/17 2:25 PM, Ross Zwisler wrote:
>>>>> Add a new 'log_writes' command to xfs_io so that we can add dm-log-writes
>>>>> log marks via the external 'dmsetup' executable.  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>
>>>>
>>>> Without reviewing in detail, what is the advantage of wrapping dmsetup
>>>> into xfs_io?  My first inclination is that there is none at all, and
>>>> xfstests can call dmsetup as easily as they can call xfs_io.  No?
>>>>
>>>> -Eric
>>>
>>> I commented on this a bit in the changelog for the 2nd patch:
>>>
>>> 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.
>>>
>>> I agree that the shell-out to dmsetup isn't awesome...  For the current test I
>>> have written I think we can get away with just assuming that the xfs_io exit
>>> stuff won't interact too heavily with the dm-log-writes log, and we could
>>> potentially move the dmsetup call back into the fstest.  This is how I
>>> initially had it, and moved it into the C program via shell-out in response to
>>> Amir's feedback:
>>
>> Sorry, terrible of me to not have read that.  :(  Ok, so next question - 
>> DM_TARGET_MSG seems to be public, can we just invoke the ioctl directly
>> instead of shelling out to dmsetup?
>>
>> I'm checking w/ the dm folks too, to make sure that's expected to work.  As
>> long as the use isn't too tricky it seems like that might be better.
> 
> Yea, that seems like a better option - I'll take a look.  Thanks for the
> suggestion.

FWIW, agk is saying the only right way to do it is to use libdevicemapper ...
sounds like they don't expect anyone to use the ioctl directly, though I'm
not sure why, or what the complexity is.

-Eric

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

[Darrick J. Wong]

On Fri, Nov 17, 2017 at 01:25:24PM -0700, Ross Zwisler wrote:
> Add a new 'log_writes' command to xfs_io so that we can add dm-log-writes
> log marks via the external 'dmsetup' executable.  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>
> ---
>  io/Makefile       |  5 ++--
>  io/init.c         |  1 +
>  io/io.h           |  1 +
>  io/log_writes.c   | 78 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  man/man8/xfs_io.8 | 19 ++++++++++++++
>  5 files changed, 102 insertions(+), 2 deletions(-)
>  create mode 100644 io/log_writes.c
> 
> diff --git a/io/Makefile b/io/Makefile
> index 050d6bd..51b2eae 100644
> --- a/io/Makefile
> +++ b/io/Makefile
> @@ -10,8 +10,9 @@ LSRCFILES = xfs_bmap.sh xfs_freeze.sh xfs_mkfile.sh
>  HFILES = init.h io.h
>  CFILES = init.c \
>  	attr.c bmap.c cowextsize.c encrypt.c file.c freeze.c fsync.c \
> -	getrusage.c imap.c link.c mmap.c open.c parent.c pread.c prealloc.c \
> -	pwrite.c reflink.c seek.c shutdown.c stat.c sync.c truncate.c utimes.c
> +	getrusage.c imap.c link.c log_writes.c mmap.c open.c parent.c pread.c \
> +	prealloc.c pwrite.c reflink.c seek.c shutdown.c stat.c sync.c \
> +	truncate.c utimes.c
>  
>  LLDLIBS = $(LIBXCMD) $(LIBHANDLE) $(LIBPTHREAD)
>  LTDEPENDENCIES = $(LIBXCMD) $(LIBHANDLE)
> diff --git a/io/init.c b/io/init.c
> index 20d5f80..34d87b5 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 8b2753b..d62034a 100644
> --- a/io/io.h
> +++ b/io/io.h
> @@ -109,6 +109,7 @@ extern void		getrusage_init(void);
>  extern void		help_init(void);
>  extern void		imap_init(void);
>  extern void		inject_init(void);
> +extern void		log_writes_init(void);
>  extern void		mmap_init(void);
>  extern void		open_init(void);
>  extern void		parent_init(void);
> diff --git a/io/log_writes.c b/io/log_writes.c
> new file mode 100644
> index 0000000..bc3952c
> --- /dev/null
> +++ b/io/log_writes.c
> @@ -0,0 +1,78 @@
> +/*
> + * 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 "command.h"
> +#include "init.h"
> +
> +static cmdinfo_t log_writes_cmd;
> +
> +static int
> +mark_log(char *device, char *mark)
> +{
> +	char command[256];
> +
> +	snprintf(command, 256, "dmsetup message %s 0 mark %s",
> +			device, mark);
> +
> +	return system(command);

I want to call my mark "bobby'; DROP TABLES;"... ;)

Maybe we should check snprintf return value just in case someone feeds
us an overlong string?

--D

> +}
> +
> +static int
> +log_writes_f(
> +	int			argc,
> +	char			**argv)
> +{
> +	char *device = NULL;
> +	char *mark = NULL;
> +	int c;
> +
> +	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);
> +
> +	return mark_log(device, mark);
> +}
> +
> +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;
> +	log_writes_cmd.argmin = 0;
> +	log_writes_cmd.argmax = -1;
> +	log_writes_cmd.args = _("-d device -m mark");
> +	log_writes_cmd.oneline =
> +		_("uses dmsetup to interact with the dm-log-writes module");
> +
> +	add_command(&log_writes_cmd);
> +}
> diff --git a/man/man8/xfs_io.8 b/man/man8/xfs_io.8
> index 1693f7f..f18af99 100644
> --- a/man/man8/xfs_io.8
> +++ b/man/man8/xfs_io.8
> @@ -1123,7 +1123,25 @@ 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
> +Use
> +.B dmsetup
> +to interact with the
> +.B dm-log-writes
> +kernel module.  Currently the only operation
> +supported is the creation of a mark in the log by executing the shell command:
>  
> +.B dmsetup message <device> 0 mark <mark>
> +.PD
> +.RE
> +.TP
> +.B lw
> +See the
> +.B log_writes
> +command.
>  .SH SEE ALSO
>  .BR mkfs.xfs (8),
>  .BR xfsctl (3),
> @@ -1142,3 +1160,4 @@ current file.
>  .BR pread (2),
>  .BR pwrite (2),
>  .BR readdir (3).
> +.BR dmsetup (8).
> -- 
> 2.9.5
> 
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