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Switch git_mmap to use pread.

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Now that Git depends on pread in index-pack its safe to say we can
also depend on it within the git_mmap emulation we activate when
NO_MMAP is set.  On most systems pread should be slightly faster
than an lseek/read/lseek sequence as its one system call vs. three
system calls.

We also now honor EAGAIN and EINTR error codes from pread and
restart the prior read.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>
This commit is contained in:
Shawn O. Pearce 2006-12-24 00:45:47 -05:00 committed by Junio C Hamano
parent d6779124b9
commit 8e554429e8
1 changed files with 5 additions and 14 deletions
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19
compat/mmap.c
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@ -2,17 +2,11 @@
void *git_mmap(void *start, size_t length, int prot, int flags, int fd, off_t offset) void *git_mmap(void *start, size_t length, int prot, int flags, int fd, off_t offset)
{ {
int n = 0; size_t n = 0;
off_t current_offset = lseek(fd, 0, SEEK_CUR);
if (start != NULL || !(flags & MAP_PRIVATE)) if (start != NULL || !(flags & MAP_PRIVATE))
die("Invalid usage of mmap when built with NO_MMAP"); die("Invalid usage of mmap when built with NO_MMAP");
if (lseek(fd, offset, SEEK_SET) < 0) {
errno = EINVAL;
return MAP_FAILED;
}
start = xmalloc(length); start = xmalloc(length);
if (start == NULL) { if (start == NULL) {
errno = ENOMEM; errno = ENOMEM;
@ -20,14 +14,16 @@ void *git_mmap(void *start, size_t length, int prot, int flags, int fd, off_t of
} }
while (n < length) { while (n < length) {
int count = read(fd, start+n, length-n); ssize_t count = pread(fd, (char *)start + n, length - n, offset + n);
if (count == 0) { if (count == 0) {
memset(start+n, 0, length-n); memset((char *)start+n, 0, length-n);
break; break;
} }
if (count < 0) { if (count < 0) {
if (errno == EAGAIN || errno == EINTR)
continue;
free(start); free(start);
errno = EACCES; errno = EACCES;
return MAP_FAILED; return MAP_FAILED;
@ -36,11 +32,6 @@ void *git_mmap(void *start, size_t length, int prot, int flags, int fd, off_t of
n += count; n += count;
} }
if (current_offset != lseek(fd, current_offset, SEEK_SET)) {
errno = EINVAL;
return MAP_FAILED;
}
return start; return start;
} }