On Wed, May 22, 2019 at 5:08 PM Laurent Vivier <laur...@vivier.eu> wrote: > > On 14/05/2019 16:53, Chen-Yu Tsai wrote: > > From: Chen-Yu Tsai <w...@csie.org> > > > > Since Linux 2.6 the stat syscalls have mostly supported nanosecond > > components for each of the file-related timestamps. > > > > QEMU user mode emulation currently does not pass through the nanosecond > > portion of the timestamp, even when the host system fills in the value. > > This results in a mismatch when run on subsecond resolution filesystems > > such as ext4 or XFS. > > > > An example of this leading to inconsistency is cross-debootstraping a > > full desktop root filesystem of Debian Buster. Recent versions of > > fontconfig store the full timestamp (instead of just the second portion) > > of the directory in its per-directory cache file, and checks this against > > the directory to see if the cache is up-to-date. With QEMU user mode > > emulation, the timestamp stored is incorrect, and upon booting the rootfs > > natively, fontconfig discovers the mismatch, and proceeds to rebuild the > > cache on the comparatively slow machine (low-power ARM vs x86). This > > stalls the first attempt to open whatever application that incorporates > > fontconfig. > > > > This patch renames the "unused" padding trailing each timestamp element > > to its nanosecond counterpart name if such an element exists in the > > kernel sources for the given platform. Not all do. Then have the syscall > > wrapper fill in the nanosecond portion if the host supports it, as > > specified by the _POSIX_C_SOURCE and _XOPEN_SOURCE feature macros. > > > > Recent versions of glibc only use stat64 and newfstatat syscalls on > > 32-bit and 64-bit platforms respectively. The changes in this patch > > were tested by directly calling the stat, stat64 and newfstatat syscalls > > directly, in addition to the glibc wrapper, on arm and aarch64 little > > endian targets. > > > > Signed-off-by: Chen-Yu Tsai <w...@csie.org> > > > > --- > > > > This issue was found while integrating some software that uses newer > > versions of fontconfig into Raspbian images. We found that the first > > launch of said software always stalls with fontconfig regenerating its > > font cache files. Upon closer examination I found the timestamps were > > not matching. The rest is explained above. Currently we're just working > > around the problem by patching the correct timestamps into the cache > > files after the fact. > > > > Please consider this a drive-by scratch-my-own-itch contribution, but I > > will stick around to deal with any comments raised during review. I'm > > not on the mailing lists either, so please keep me in CC. > > > > checkpatch returns "ERROR: code indent should never use tabs" for > > linux-user/syscall_defs.h, however as far as I can tell the whole file > > is indented with tabs. I'm not sure what to make of this. > > Yes, the file is entirely indented with tabs, so you can let this as-is. > Anyway, I plan to split the file in several ones so we will be able to > swap the tabs with spaces. > > Reviewed-by: Laurent Vivier <laur...@vivier.eu>
Thanks. Unfortunately this patch has some issues. It fails to build for targets that don't have the *_nsec fields, such as Alpha or M68K. I'll spin a v2 with a new macro TARGET_STAT_HAS_NSEC defined for targets that have the fields, added before each struct stat definition. The hunk below will gain a check against said macro. This is pretty much how the kernel deals with the difference as well, as I just found out. > > @@ -8866,6 +8876,14 @@ static abi_long do_syscall1(void *cpu_env, int num, > > abi_long arg1, > > __put_user(st.st_atime, &target_st->target_st_atime); > > __put_user(st.st_mtime, &target_st->target_st_mtime); > > __put_user(st.st_ctime, &target_st->target_st_ctime); > > +#if _POSIX_C_SOURCE >= 200809L || _XOPEN_SOURCE >= 700 > > + __put_user(st.st_atim.tv_nsec, > > + &target_st->target_st_atime_nsec); > > + __put_user(st.st_mtim.tv_nsec, > > + &target_st->target_st_mtime_nsec); > > + __put_user(st.st_ctim.tv_nsec, > > + &target_st->target_st_ctime_nsec); > > +#endif > > unlock_user_struct(target_st, arg2, 1); > > } > > } If that sounds good to you I'll keep your reviewed-by for v2. Thanks ChenYu
