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Make loose object file reading more careful

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We used to do 'stat()+open()+mmap()+close()' to read the loose object
file data, which does work fine, but has a couple of problems:

 - it unnecessarily walks the filename twice (at 'stat()' time and then
   again to open it)

 - NFS generally has open-close consistency guarantees, which means that
   the initial 'stat()' was technically done outside of the normal
   consistency rules.

So change it to do 'open()+fstat()+mmap()+close()' instead, which avoids
both these issues.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Linus Torvalds 2008-06-14 11:32:37 -07:00 committed by Junio C Hamano
parent 5723fe7e3c
commit 44d1c19ee8
1 changed files with 44 additions and 26 deletions
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70
sha1_file.c
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@ -35,8 +35,6 @@ static size_t sz_fmt(size_t s) { return s; }
const unsigned char null_sha1[20];
static unsigned int sha1_file_open_flag = O_NOATIME;
const signed char hexval_table[256] = {
-1, -1, -1, -1, -1, -1, -1, -1, /* 00-07 */
-1, -1, -1, -1, -1, -1, -1, -1, /* 08-0f */
@ -997,38 +995,58 @@ int check_sha1_signature(const unsigned char *sha1, void *map, unsigned long siz
return hashcmp(sha1, real_sha1) ? -1 : 0;
}
static int git_open_noatime(const char *name)
{
static int sha1_file_open_flag = O_NOATIME;
int fd = open(name, O_RDONLY | sha1_file_open_flag);
/* Might the failure be due to O_NOATIME? */
if (fd < 0 && errno != ENOENT && sha1_file_open_flag) {
fd = open(name, O_RDONLY);
if (fd >= 0)
sha1_file_open_flag = 0;
}
return fd;
}
static int open_sha1_file(const unsigned char *sha1)
{
int fd;
char *name = sha1_file_name(sha1);
struct alternate_object_database *alt;
fd = git_open_noatime(name);
if (fd >= 0)
return fd;
prepare_alt_odb();
errno = ENOENT;
for (alt = alt_odb_list; alt; alt = alt->next) {
name = alt->name;
fill_sha1_path(name, sha1);
fd = git_open_noatime(alt->base);
if (fd >= 0)
return fd;
}
return -1;
}
static void *map_sha1_file(const unsigned char *sha1, unsigned long *size)
{
struct stat st;
void *map;
int fd;
char *filename = find_sha1_file(sha1, &st);
if (!filename) {
return NULL;
}
fd = open_sha1_file(sha1);
map = NULL;
if (fd >= 0) {
struct stat st;
fd = open(filename, O_RDONLY | sha1_file_open_flag);
if (fd < 0) {
/* See if it works without O_NOATIME */
switch (sha1_file_open_flag) {
default:
fd = open(filename, O_RDONLY);
if (fd >= 0)
break;
/* Fallthrough */
case 0:
return NULL;
if (!fstat(fd, &st)) {
*size = xsize_t(st.st_size);
map = xmmap(NULL, *size, PROT_READ, MAP_PRIVATE, fd, 0);
}
/* If it failed once, it will probably fail again.
* Stop using O_NOATIME
*/
sha1_file_open_flag = 0;
close(fd);
}
*size = xsize_t(st.st_size);
map = xmmap(NULL, *size, PROT_READ, MAP_PRIVATE, fd, 0);
close(fd);
return map;
}