libxfs: stop overriding MAP_SYNC in publicly exported header files
Florian Fainelli most recently reported that xfsprogs doesn't build with
musl on mips:
"MIPS platforms building with recent kernel headers and the musl-libc
toolchain will expose the following build failure:
mmap.c: In function 'mmap_f':
mmap.c:196:12: error: 'MAP_SYNC' undeclared (first use in this function); did you mean 'MS_SYNC'?
196 | flags = MAP_SYNC | MAP_SHARED_VALIDATE;
| ^~~~~~~~
| MS_SYNC
mmap.c:196:12: note: each undeclared identifier is reported only once for each function it appears in
make[4]: *** [../include/buildrules:81: mmap.o] Error 1"
At first glance, the build failure here is caused by the fact that:
1. The configure script doesn't detect MAP_SYNC support
2. The build system doesn't set HAVE_MAP_SYNC
2. io/mmap.c includes input.h -> projects.h -> xfs.h and later sys/mman.h
3. include/linux.h #define's MAP_SYNC to 0 if HAVE_MAP_SYNC is not set
4. musl's sys/mman.h #undef MAP_SYNC on platforms that don't support it
5. io/mmap.c tries to use MAP_SYNC, not realizing that libc undefined it
Normally, xfs_io only exports functionality that is defined by the libc
and/or kernel headers on the build system. We often make exceptions for
new functionality so that we have a way to test them before the header
file packages catch up, hence this '#ifndef HAVE_FOO #define FOO'
paradigm.
MAP_SYNC is a gross and horribly broken example of this. These support
crutches are supposed to be *private* to xfsprogs for benefit of early
testing, but they were instead added to include/linux.h, which we
provide to user programs in the xfslibs-dev package. IOWs, we've been
#defining MAP_SYNC to zero for unsuspecting programs.
Worst yet, gcc 11.3 doesn't even warn about overriding a #define to 0:
#include <stdio.h>
#include <sys/mman.h>
#ifdef STUPID
# include <xfs/xfs.h>
#endif
int main(int argc, char *argv[]) {
printf("MAP_SYNC 0x%x\n", MAP_SYNC);
}
$ gcc -o a a.c -Wall
$ ./a
MAP_SYNC 0x80000
$ gcc -DSTUPID -o a a.c -Wall
$ ./a
MAP_SYNC 0x0
Four years have gone by since the introduction of MAP_SYNC, so let's get
rid of the override code entirely -- any platform that supports MAP_SYNC
has had plenty of chances to ensure their header files have the right
bits. While we're at it, fix AC_HAVE_MAP_SYNC to look for MAP_SYNC in
the same header file that the one user (io/mmap.c) uses -- sys/mman.h.
Annoyingly, I had to test this by hand because the sole fstest that
exercises MAP_SYNC (generic/470) requires dm-logwrites and dm-thinp,
neither of which support fsdax on current kernels.
Reported-by: info@mobile-stream.com
Reported-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Reported-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Tested-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Carlos Maiolino <cmaiolino@redhat.com>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>
4 files changed
