From b82bd75c80aadcc2890b23f63eec9ba2c560b2e5 Mon Sep 17 00:00:00 2001 From: "Darrick J. Wong" Date: Thu, 4 Aug 2022 21:26:43 -0500 Subject: [PATCH] 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 Worst yet, gcc 11.3 doesn't even warn about overriding a #define to 0: 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 Reported-by: Florian Fainelli Signed-off-by: Darrick J. Wong Tested-by: Florian Fainelli Reviewed-by: Carlos Maiolino Signed-off-by: Eric Sandeen --- include/linux.h | 8 -------- io/io.h | 2 +- io/mmap.c | 25 +++++++++++++------------ m4/package_libcdev.m4 | 3 +-- 4 files changed, 15 insertions(+), 23 deletions(-) diff --git a/include/linux.h b/include/linux.h index de8a71221146..052facc15db5 100644 --- a/include/linux.h +++ b/include/linux.h @@ -356,14 +356,6 @@ fsmap_advance( #define HAVE_GETFSMAP #endif /* HAVE_GETFSMAP */ -#ifndef HAVE_MAP_SYNC -#define MAP_SYNC 0 -#define MAP_SHARED_VALIDATE 0 -#else -#include -#include -#endif /* HAVE_MAP_SYNC */ - /* * Reminder: anything added to this file will be compiled into downstream * userspace projects! diff --git a/io/io.h b/io/io.h index 49db902fc44f..64b7a663a8cf 100644 --- a/io/io.h +++ b/io/io.h @@ -55,7 +55,7 @@ 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? */ + int flags; /* MAP_* flags passed to mmap() */ char *name; /* name of backing file */ } mmap_region_t; diff --git a/io/mmap.c b/io/mmap.c index 8c048a0ab6d0..425957d4b487 100644 --- a/io/mmap.c +++ b/io/mmap.c @@ -46,8 +46,11 @@ 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) +#ifdef HAVE_MAP_SYNC + if ((map->flags & (MAP_SYNC | MAP_SHARED_VALIDATE)) == + (MAP_SYNC | MAP_SHARED_VALIDATE)) sprintf(&buffer[i], " S"); +#endif printf("%c%03d%c 0x%lx - 0x%lx %s %14s (%lld : %ld)\n", braces? '[' : ' ', index, braces? ']' : ' ', @@ -139,7 +142,9 @@ mmap_help(void) " -r -- map with PROT_READ protection\n" " -w -- map with PROT_WRITE protection\n" " -x -- map with PROT_EXEC protection\n" +#ifdef HAVE_MAP_SYNC " -S -- map with MAP_SYNC and MAP_SHARED_VALIDATE flags\n" +#endif " -s -- 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")); @@ -193,18 +198,14 @@ mmap_f( prot |= PROT_EXEC; break; case 'S': +#ifdef HAVE_MAP_SYNC 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; +#else + printf("MAP_SYNC not supported\n"); + exitcode = 1; + return command_usage(&mmap_cmd); +#endif case 's': length2 = cvtnum(blocksize, sectsize, optarg); break; @@ -281,7 +282,7 @@ mmap_f( mapping->offset = offset; mapping->name = filename; mapping->prot = prot; - mapping->map_sync = (flags == (MAP_SYNC | MAP_SHARED_VALIDATE)); + mapping->flags = flags; return 0; } diff --git a/m4/package_libcdev.m4 b/m4/package_libcdev.m4 index adab9bb9773a..3a0c23453176 100644 --- a/m4/package_libcdev.m4 +++ b/m4/package_libcdev.m4 @@ -339,8 +339,7 @@ AC_DEFUN([AC_HAVE_STATFS_FLAGS], AC_DEFUN([AC_HAVE_MAP_SYNC], [ AC_MSG_CHECKING([for MAP_SYNC]) AC_TRY_COMPILE([ -#include -#include +#include ], [ int flags = MAP_SYNC | MAP_SHARED_VALIDATE; ], have_map_sync=yes -- 2.25.1