From: Chen-Yu Tsai <address@hidden>
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 <address@hidden>
---
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.
Finally, I think this could be worth backporting to older versions.
---
linux-user/syscall.c | 18 ++++++++++++++++++
linux-user/syscall_defs.h | 36 ++++++++++++++++++------------------
2 files changed, 36 insertions(+), 18 deletions(-)
diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index f5ff6f5dc8..dcd6f5d806 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -6408,6 +6408,11 @@ static inline abi_long host_to_target_stat64(void
*cpu_env,
__put_user(host_st->st_atime, &target_st->target_st_atime);
__put_user(host_st->st_mtime, &target_st->target_st_mtime);
__put_user(host_st->st_ctime, &target_st->target_st_ctime);
+#if _POSIX_C_SOURCE >= 200809L || _XOPEN_SOURCE >= 700
+ __put_user(host_st->st_atim.tv_nsec, &target_st->target_st_atime_nsec);
+ __put_user(host_st->st_mtim.tv_nsec, &target_st->target_st_mtime_nsec);
+ __put_user(host_st->st_ctim.tv_nsec, &target_st->target_st_ctime_nsec);
+#endif
unlock_user_struct(target_st, target_addr, 1);
} else
#endif
@@ -6438,6 +6443,11 @@ static inline abi_long host_to_target_stat64(void
*cpu_env,
__put_user(host_st->st_atime, &target_st->target_st_atime);
__put_user(host_st->st_mtime, &target_st->target_st_mtime);
__put_user(host_st->st_ctime, &target_st->target_st_ctime);
+#if _POSIX_C_SOURCE >= 200809L || _XOPEN_SOURCE >= 700
+ __put_user(host_st->st_atim.tv_nsec, &target_st->target_st_atime_nsec);
+ __put_user(host_st->st_mtim.tv_nsec, &target_st->target_st_mtime_nsec);
+ __put_user(host_st->st_ctim.tv_nsec, &target_st->target_st_ctime_nsec);
+#endif
unlock_user_struct(target_st, target_addr, 1);
}
@@ -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);
}
}
diff --git a/linux-user/syscall_defs.h b/linux-user/syscall_defs.h
index 12c8407144..252e69b76e 100644
--- a/linux-user/syscall_defs.h
+++ b/linux-user/syscall_defs.h
@@ -1192,11 +1192,11 @@ struct target_stat {
abi_ulong st_blksize;
abi_ulong st_blocks;
abi_ulong target_st_atime;
- abi_ulong __unused1;
+ abi_ulong target_st_atime_nsec;
abi_ulong target_st_mtime;
- abi_ulong __unused2;
+ abi_ulong target_st_mtime_nsec;
abi_ulong target_st_ctime;
- abi_ulong __unused3;
+ abi_ulong target_st_ctime_nsec;
abi_ulong __unused4;
abi_ulong __unused5;
};
@@ -1228,13 +1228,13 @@ struct target_stat64 {
abi_ulong __pad4; /* future possible st_blocks high bits
*/
abi_ulong target_st_atime;
- abi_ulong __pad5;
+ abi_ulong target_st_atime_nsec;
abi_ulong target_st_mtime;
- abi_ulong __pad6;
+ abi_ulong target_st_mtime_nsec;
abi_ulong target_st_ctime;
- abi_ulong __pad7; /* will be high 32 bits of ctime
someday */
+ abi_ulong target_st_ctime_nsec;
unsigned long long st_ino;
} QEMU_PACKED;
@@ -1313,13 +1313,13 @@ struct target_stat64 {
unsigned int st_blocks;
abi_ulong target_st_atime;
- abi_ulong __unused1;
+ abi_ulong target_st_atime_nsec;
abi_ulong target_st_mtime;
- abi_ulong __unused2;
+ abi_ulong target_st_mtime_nsec;
abi_ulong target_st_ctime;
- abi_ulong __unused3;
+ abi_ulong target_st_ctime_nsec;
abi_ulong __unused4[3];
};
@@ -1336,14 +1336,14 @@ struct target_stat {
unsigned short st_rdev;
abi_long st_size;
abi_long target_st_atime;
- abi_ulong __unused1;
+ abi_ulong target_st_atime_nsec;
abi_long target_st_mtime;
- abi_ulong __unused2;
+ abi_ulong target_st_mtime_nsec;
abi_long target_st_ctime;
- abi_ulong __unused3;
+ abi_ulong target_st_ctime_nsec;
abi_long st_blksize;
abi_long st_blocks;
- abi_ulong __unused4[2];
+ abi_ulong __unused1[2];
};
#define TARGET_HAS_STRUCT_STAT64
@@ -1371,16 +1371,16 @@ struct target_stat64 {
unsigned int st_blocks;
unsigned int target_st_atime;
- unsigned int __unused1;
+ unsigned int target_st_atime_nsec;
unsigned int target_st_mtime;
- unsigned int __unused2;
+ unsigned int target_st_mtime_nsec;
unsigned int target_st_ctime;
- unsigned int __unused3;
+ unsigned int target_st_ctime_nsec;
- unsigned int __unused4;
- unsigned int __unused5;
+ unsigned int __unused1;
+ unsigned int __unused2;
};
#elif defined(TARGET_PPC)