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+From b82bd75c80aadcc2890b23f63eec9ba2c560b2e5 Mon Sep 17 00:00:00 2001
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+From: "Darrick J. Wong" <djwong@kernel.org>
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+Date: Thu, 4 Aug 2022 21:26:43 -0500
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+Subject: [PATCH] libxfs: stop overriding MAP_SYNC in publicly exported header
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+ files
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+
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+Florian Fainelli most recently reported that xfsprogs doesn't build with
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+musl on mips:
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+
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+"MIPS platforms building with recent kernel headers and the musl-libc
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+toolchain will expose the following build failure:
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+
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+mmap.c: In function 'mmap_f':
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+mmap.c:196:12: error: 'MAP_SYNC' undeclared (first use in this function); did you mean 'MS_SYNC'?
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+ 196 | flags = MAP_SYNC | MAP_SHARED_VALIDATE;
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+ | ^~~~~~~~
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+ | MS_SYNC
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+mmap.c:196:12: note: each undeclared identifier is reported only once for each function it appears in
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+make[4]: *** [../include/buildrules:81: mmap.o] Error 1"
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+
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+At first glance, the build failure here is caused by the fact that:
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+
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+1. The configure script doesn't detect MAP_SYNC support
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+2. The build system doesn't set HAVE_MAP_SYNC
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+2. io/mmap.c includes input.h -> projects.h -> xfs.h and later sys/mman.h
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+3. include/linux.h #define's MAP_SYNC to 0 if HAVE_MAP_SYNC is not set
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+4. musl's sys/mman.h #undef MAP_SYNC on platforms that don't support it
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+5. io/mmap.c tries to use MAP_SYNC, not realizing that libc undefined it
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+
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+Normally, xfs_io only exports functionality that is defined by the libc
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+and/or kernel headers on the build system. We often make exceptions for
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+new functionality so that we have a way to test them before the header
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+file packages catch up, hence this '#ifndef HAVE_FOO #define FOO'
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+paradigm.
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+
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+MAP_SYNC is a gross and horribly broken example of this. These support
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+crutches are supposed to be *private* to xfsprogs for benefit of early
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+testing, but they were instead added to include/linux.h, which we
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+provide to user programs in the xfslibs-dev package. IOWs, we've been
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+
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+Worst yet, gcc 11.3 doesn't even warn about overriding a #define to 0:
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+
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+int main(int argc, char *argv[]) {
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+ printf("MAP_SYNC 0x%x\n", MAP_SYNC);
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+}
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+
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+$ gcc -o a a.c -Wall
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+$ ./a
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+MAP_SYNC 0x80000
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+$ gcc -DSTUPID -o a a.c -Wall
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+$ ./a
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+MAP_SYNC 0x0
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+
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+Four years have gone by since the introduction of MAP_SYNC, so let's get
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+rid of the override code entirely -- any platform that supports MAP_SYNC
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+has had plenty of chances to ensure their header files have the right
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+bits. While we're at it, fix AC_HAVE_MAP_SYNC to look for MAP_SYNC in
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+the same header file that the one user (io/mmap.c) uses -- sys/mman.h.
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+
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+Annoyingly, I had to test this by hand because the sole fstest that
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+exercises MAP_SYNC (generic/470) requires dm-logwrites and dm-thinp,
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+neither of which support fsdax on current kernels.
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+
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+Reported-by: info@mobile-stream.com
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+Reported-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
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+Reported-by: Florian Fainelli <f.fainelli@gmail.com>
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+Signed-off-by: Darrick J. Wong <djwong@kernel.org>
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+Tested-by: Florian Fainelli <f.fainelli@gmail.com>
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+Reviewed-by: Carlos Maiolino <cmaiolino@redhat.com>
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+Signed-off-by: Eric Sandeen <sandeen@sandeen.net>
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+---
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+ include/linux.h | 8 --------
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+ io/io.h | 2 +-
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+ io/mmap.c | 25 +++++++++++++------------
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+ m4/package_libcdev.m4 | 3 +--
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+ 4 files changed, 15 insertions(+), 23 deletions(-)
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+
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+diff --git a/include/linux.h b/include/linux.h
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+index de8a71221146..052facc15db5 100644
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+--- a/include/linux.h
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++++ b/include/linux.h
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+@@ -356,14 +356,6 @@ fsmap_advance(
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+ #define HAVE_GETFSMAP
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+ #endif /* HAVE_GETFSMAP */
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+
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+-#ifndef HAVE_MAP_SYNC
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+-#define MAP_SYNC 0
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+-#define MAP_SHARED_VALIDATE 0
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+-#else
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+-#include <asm-generic/mman.h>
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+-#include <asm-generic/mman-common.h>
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+-#endif /* HAVE_MAP_SYNC */
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+-
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+ /*
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+ * Reminder: anything added to this file will be compiled into downstream
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+ * userspace projects!
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+diff --git a/io/io.h b/io/io.h
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+index 49db902fc44f..64b7a663a8cf 100644
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+--- a/io/io.h
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++++ b/io/io.h
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+@@ -55,7 +55,7 @@ typedef struct mmap_region {
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+ size_t length; /* length of mapping */
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+ off64_t offset; /* start offset into backing file */
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+ int prot; /* protection mode of the mapping */
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+- bool map_sync; /* is this a MAP_SYNC mapping? */
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++ int flags; /* MAP_* flags passed to mmap() */
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+ char *name; /* name of backing file */
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+ } mmap_region_t;
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+
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+diff --git a/io/mmap.c b/io/mmap.c
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+index 8c048a0ab6d0..425957d4b487 100644
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+--- a/io/mmap.c
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++++ b/io/mmap.c
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+@@ -46,8 +46,11 @@ print_mapping(
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+ for (i = 0, p = pflags; p->prot != PROT_NONE; i++, p++)
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+ buffer[i] = (map->prot & p->prot) ? p->mode : '-';
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+
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+- if (map->map_sync)
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++#ifdef HAVE_MAP_SYNC
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++ if ((map->flags & (MAP_SYNC | MAP_SHARED_VALIDATE)) ==
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++ (MAP_SYNC | MAP_SHARED_VALIDATE))
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+ sprintf(&buffer[i], " S");
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++#endif
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+
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+ printf("%c%03d%c 0x%lx - 0x%lx %s %14s (%lld : %ld)\n",
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+ braces? '[' : ' ', index, braces? ']' : ' ',
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+@@ -139,7 +142,9 @@ mmap_help(void)
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+ " -r -- map with PROT_READ protection\n"
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+ " -w -- map with PROT_WRITE protection\n"
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+ " -x -- map with PROT_EXEC protection\n"
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++#ifdef HAVE_MAP_SYNC
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+ " -S -- map with MAP_SYNC and MAP_SHARED_VALIDATE flags\n"
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++#endif
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+ " -s <size> -- first do mmap(size)/munmap(size), try to reserve some free space\n"
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+ " If no protection mode is specified, all are used by default.\n"
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+ "\n"));
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+@@ -193,18 +198,14 @@ mmap_f(
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+ prot |= PROT_EXEC;
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+ break;
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+ case 'S':
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++#ifdef HAVE_MAP_SYNC
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+ flags = MAP_SYNC | MAP_SHARED_VALIDATE;
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+-
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+- /*
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+- * If MAP_SYNC and MAP_SHARED_VALIDATE aren't defined
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+- * in the system headers we will have defined them
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+- * both as 0.
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+- */
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+- if (!flags) {
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+- printf("MAP_SYNC not supported\n");
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+- return 0;
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+- }
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+ break;
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++#else
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++ printf("MAP_SYNC not supported\n");
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++ exitcode = 1;
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++ return command_usage(&mmap_cmd);
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++#endif
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+ case 's':
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+ length2 = cvtnum(blocksize, sectsize, optarg);
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+ break;
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+@@ -281,7 +282,7 @@ mmap_f(
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+ mapping->offset = offset;
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+ mapping->name = filename;
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+ mapping->prot = prot;
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+- mapping->map_sync = (flags == (MAP_SYNC | MAP_SHARED_VALIDATE));
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++ mapping->flags = flags;
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+ return 0;
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+ }
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+
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+diff --git a/m4/package_libcdev.m4 b/m4/package_libcdev.m4
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+index adab9bb9773a..3a0c23453176 100644
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+--- a/m4/package_libcdev.m4
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++++ b/m4/package_libcdev.m4
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+@@ -339,8 +339,7 @@ AC_DEFUN([AC_HAVE_STATFS_FLAGS],
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+ AC_DEFUN([AC_HAVE_MAP_SYNC],
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+ [ AC_MSG_CHECKING([for MAP_SYNC])
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+ AC_TRY_COMPILE([
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+-#include <asm-generic/mman.h>
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+-#include <asm-generic/mman-common.h>
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++#include <sys/mman.h>
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+ ], [
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+ int flags = MAP_SYNC | MAP_SHARED_VALIDATE;
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+ ], have_map_sync=yes
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+--
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+2.25.1
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+
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Florian Fainelli