mirrors/git
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

git_open(): untangle possible NOATIME and CLOEXEC interactions

Browse Source 
The way we structured the fallback/retry mechanism for opening with
O_NOATIME and O_CLOEXEC meant that if we failed due to lack of
support to open the file with O_NOATIME option (i.e. EINVAL), we
would still try to drop O_CLOEXEC first and retry, and then drop
O_NOATIME.  A platform on which O_NOATIME is defined in the header
without support from the kernel wouldn't have a chance to open with
O_CLOEXEC option due to this code structure.

Arguably, O_CLOEXEC is more important than O_NOATIME, as the latter
is mostly about performance, while the former can affect correctness.

Instead use O_CLOEXEC to open the file, and then use fcntl(2) to set
O_NOATIME on the resulting file descriptor.  open(2) itself does not
cause atime to be updated according to Linus [*1*].

The helper to do the former can be usable in the codepath in
ce_compare_data() that was recently added to open a file descriptor
with O_CLOEXEC; use it while we are at it.

*1* <CA+55aFw83E+zOd+z5h-CA-3NhrLjVr-anL6pubrSWttYx3zu8g@mail.gmail.com>

Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Junio C Hamano
2016-10-28 06:23:07 -07:00
parent a0a6cb9662
commit 1b8ac5ead5
3 changed files with 22 additions and 29 deletions
Download Patch File Download Diff File Expand all files Collapse all files

9
read-cache.c
View File

@ -156,14 +156,7 @@ void fill_stat_cache_info(struct cache_entry *ce, struct stat *st)
static int ce_compare_data(const struct cache_entry *ce, struct stat *st)
{
int match = -1;
static int cloexec = O_CLOEXEC;
int fd = open(ce->name, O_RDONLY | cloexec);
if ((cloexec & O_CLOEXEC) && fd < 0 && errno == EINVAL) {
/* Try again w/o O_CLOEXEC: the kernel might not support it */
cloexec &= ~O_CLOEXEC;
fd = open(ce->name, O_RDONLY | cloexec);
}
int fd = git_open_cloexec(ce->name, O_RDONLY);
if (fd >= 0) {
unsigned char sha1[20];