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

Ross Zwisler
2017-12-21T22:08:10Z

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