Junio C Hamano <gits...@pobox.com> writes:
> Hmph. This may not fly well in practice, though.
We can flip the order around, and then it becomes simpler to later
drop atime support. The first step goes like this.
-- >8 --
From: Junio C Hamano <gits...@pobox.com>
Date: Fri, 28 Oct 2016 06:23:07 -0700
Subject: [PATCH] git_open(): untangle possible NOATIME and CLOEXEC interactions
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-anl6pubrswttyx3z...@mail.gmail.com>
Signed-off-by: Junio C Hamano <gits...@pobox.com>
---
cache.h | 1 +
read-cache.c | 9 +--------
sha1_file.c | 39 +++++++++++++++++++--------------------
3 files changed, 21 insertions(+), 28 deletions(-)
diff --git a/cache.h b/cache.h
index a902ca1f8e..6f1c21a352 100644
--- a/cache.h
+++ b/cache.h
@@ -1122,6 +1122,7 @@ extern int write_sha1_file(const void *buf, unsigned long
len, const char *type,
extern int hash_sha1_file_literally(const void *buf, unsigned long len, const
char *type, unsigned char *sha1, unsigned flags);
extern int pretend_sha1_file(void *, unsigned long, enum object_type, unsigned
char *);
extern int force_object_loose(const unsigned char *sha1, time_t mtime);
+extern int git_open_cloexec(const char *name, int flags);
extern int git_open(const char *name);
extern void *map_sha1_file(const unsigned char *sha1, unsigned long *size);
extern int unpack_sha1_header(git_zstream *stream, unsigned char *map,
unsigned long mapsize, void *buffer, unsigned long bufsiz);
diff --git a/read-cache.c b/read-cache.c
index db5d910642..c27d3e240b 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -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];
diff --git a/sha1_file.c b/sha1_file.c
index 09045df1dc..dfbf398183 100644
--- a/sha1_file.c
+++ b/sha1_file.c
@@ -1559,31 +1559,30 @@ int check_sha1_signature(const unsigned char *sha1,
void *map,
return hashcmp(sha1, real_sha1) ? -1 : 0;
}
-int git_open(const char *name)
+int git_open_cloexec(const char *name, int flags)
{
- static int sha1_file_open_flag = O_NOATIME | O_CLOEXEC;
-
- for (;;) {
- int fd;
-
- errno = 0;
- fd = open(name, O_RDONLY | sha1_file_open_flag);
- if (fd >= 0)
- return fd;
+ static int cloexec = O_CLOEXEC;
+ int fd = open(name, flags | cloexec);
+ if ((cloexec & O_CLOEXEC) && fd < 0 && errno == EINVAL) {
/* Try again w/o O_CLOEXEC: the kernel might not support it */
- if ((sha1_file_open_flag & O_CLOEXEC) && errno == EINVAL) {
- sha1_file_open_flag &= ~O_CLOEXEC;
- continue;
- }
+ cloexec &= ~O_CLOEXEC;
+ fd = open(name, flags | cloexec);
+ }
+ return fd;
+}
- /* Might the failure be due to O_NOATIME? */
- if (errno != ENOENT && (sha1_file_open_flag & O_NOATIME)) {
- sha1_file_open_flag &= ~O_NOATIME;
- continue;
- }
- return -1;
+int git_open(const char *name)
+{
+ static int noatime = O_NOATIME;
+ int fd = git_open_cloexec(name, O_RDONLY);
+
+ if (0 <= fd && (noatime & O_NOATIME)) {
+ int flags = fcntl(fd, F_GETFL);
+ if (fcntl(fd, F_SETFL, flags | noatime))
+ noatime = 0;
}
+ return fd;
}
static int stat_sha1_file(const unsigned char *sha1, struct stat *st)
--
2.10.1-791-g404733b9cf
