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Minor improvements to write-region heuristic

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* src/androidvfs.c (android_saf_stat): Set STATB->st_dev.
(android_fstat): Likewise.
(NATIVE_NAME): Seek to start of file after truncation.
* src/fileio.c (write_region): Use stat instead of open+fstat
to obtain updated mtime.
This commit is contained in:
Po Lu 2023-08-08 16:02:49 +08:00
parent 27a57f4cca
commit 27113c22f7
2 changed files with 50 additions and 35 deletions
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15
src/androidvfs.c
View file

@ -4013,6 +4013,7 @@ android_saf_stat (const char *uri_name, const char *id_name,
memset (statb, 0, sizeof *statb);
statb->st_size = MAX (0, MIN (TYPE_MAXIMUM (off_t), size));
statb->st_mode = mode;
statb->st_dev = -4;
#ifdef STAT_TIMESPEC
STAT_TIMESPEC (statb, st_mtim).tv_sec = mtim / 1000;
STAT_TIMESPEC (statb, st_mtim).tv_nsec = (mtim % 1000) * 1000000;
@ -6169,7 +6170,14 @@ NATIVE_NAME (safPostRequest) (JNIEnv *env, jobject object)
JNIEXPORT jboolean JNICALL
NATIVE_NAME (ftruncate) (JNIEnv *env, jobject object, jint fd)
{
return ftruncate (fd, 0) != -1;
if (ftruncate (fd, 0) < 0)
return false;
/* Reset the file pointer. */
if (lseek (fd, 0, SEEK_SET) < 0)
return false;
return true;
}
#ifdef __clang__
@ -6722,6 +6730,11 @@ android_fstat (int fd, struct stat *statb)
parcel_fd = open_parcel_fds;
for (; parcel_fd; parcel_fd = parcel_fd->next)
{
if (parcel_fd->fd == fd)
/* Set STATB->st_dev to a negative device number, signifying
that it's contained within a content provider. */
statb->st_dev = -4;
if (parcel_fd->fd == fd
&& timespec_valid_p (parcel_fd->mtime))
{

70
src/fileio.c
View file

@ -5582,42 +5582,44 @@ write_region (Lisp_Object start, Lisp_Object end, Lisp_Object filename,
if (timespec_valid_p (modtime)
&& ! (valid_timestamp_file_system && st.st_dev == timestamp_file_system))
{
int desc1 = emacs_open (fn, O_WRONLY, 0);
if (desc1 >= 0)
{
struct stat st1;
if (sys_fstat (desc1, &st1) == 0
&& st.st_dev == st1.st_dev && st.st_ino == st1.st_ino)
{
/* Use the heuristic if it appears to be valid. With neither
O_EXCL nor O_TRUNC, if Emacs happened to write nothing to the
file, the time stamp won't change. Also, some non-POSIX
systems don't update an empty file's time stamp when
truncating it. Finally, file systems with 100 ns or worse
resolution sometimes seem to have bugs: on a system with ns
resolution, checking ns % 100 incorrectly avoids the heuristic
1% of the time, but the problem should be temporary as we will
try again on the next time stamp. */
bool use_heuristic
= ((open_flags & (O_EXCL | O_TRUNC)) != 0
&& st.st_size != 0
&& modtime.tv_nsec % 100 != 0);
struct stat st1;
struct timespec modtime1 = get_stat_mtime (&st1);
if (use_heuristic
&& timespec_cmp (modtime, modtime1) == 0
&& st.st_size == st1.st_size)
{
timestamp_file_system = st.st_dev;
valid_timestamp_file_system = 1;
}
else
{
st.st_size = st1.st_size;
modtime = modtime1;
}
/* The code below previously tried to open FN O_WRONLY,
subsequently calling fstat on the opened file descriptor.
This proved inefficient and resulted in FN being truncated
under several Android filesystems, and as such has been
changed to a call to `stat'. */
if (emacs_fstatat (AT_FDCWD, fn, &st1, 0) == 0
&& st.st_dev == st1.st_dev && st.st_ino == st1.st_ino)
{
/* Use the heuristic if it appears to be valid. With neither
O_EXCL nor O_TRUNC, if Emacs happened to write nothing to the
file, the time stamp won't change. Also, some non-POSIX
systems don't update an empty file's time stamp when
truncating it. Finally, file systems with 100 ns or worse
resolution sometimes seem to have bugs: on a system with ns
resolution, checking ns % 100 incorrectly avoids the heuristic
1% of the time, but the problem should be temporary as we will
try again on the next time stamp. */
bool use_heuristic
= ((open_flags & (O_EXCL | O_TRUNC)) != 0
&& st.st_size != 0
&& modtime.tv_nsec % 100 != 0);
struct timespec modtime1 = get_stat_mtime (&st1);
if (use_heuristic
&& timespec_cmp (modtime, modtime1) == 0
&& st.st_size == st1.st_size)
{
timestamp_file_system = st.st_dev;
valid_timestamp_file_system = 1;
}
else
{
st.st_size = st1.st_size;
modtime = modtime1;
}
emacs_close (desc1);
}
}