On Wed, Jul 20, 2022 at 04:28:00PM -0700, Darrick J. Wong wrote:
> Can one of you please apply this patch and see if it'll build in musl on
> mips, please? Sorry it's taken so long to address this. :/
>
> --D
>
> ---
> From: Darrick J. Wong <djwong@xxxxxxxxxx>
>
> 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@xxxxxxxxxxxxxxxxx
> Reported-by: Fabrice Fontaine <fontaine.fabrice@xxxxxxxxx>
> Reported-by: Florian Fainelli <f.fainelli@xxxxxxxxx>
> Signed-off-by: Darrick J. Wong <djwong@xxxxxxxxxx>
> ---
> 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 3d9f4e3d..eddc4ad9 100644
> --- a/include/linux.h
> +++ b/include/linux.h
> @@ -251,14 +251,6 @@ struct fsxattr {
> #define FS_XFLAG_COWEXTSIZE 0x00010000 /* CoW extent size allocator hint */
> #endif
>
> -#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 */
> -
> /*
> * Reminder: anything added to this file will be compiled into downstream
> * userspace projects!
> diff --git a/io/io.h b/io/io.h
> index ada0a149..de4ef607 100644
> --- a/io/io.h
> +++ b/io/io.h
> @@ -58,7 +58,7 @@ 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 8c048a0a..425957d4 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 <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"));
> @@ -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 df44174d..5293dd1a 100644
> --- a/m4/package_libcdev.m4
> +++ b/m4/package_libcdev.m4
> @@ -387,8 +387,7 @@ AC_DEFUN([AC_HAVE_MAP_SYNC],
> [ AC_MSG_CHECKING([for MAP_SYNC])
> AC_COMPILE_IFELSE(
> [ AC_LANG_PROGRAM([[
> -#include <asm-generic/mman.h>
> -#include <asm-generic/mman-common.h>
> +#include <sys/mman.h>
> ]], [[
> int flags = MAP_SYNC | MAP_SHARED_VALIDATE;
> ]])
Patch looks good, if you plan to make it into a non-RFC patch, feel free to
include:
Reviewed-by: Carlos Maiolino <cmaiolino@xxxxxxxxxx>
Cheers.
--
Carlos Maiolino
