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@xxxxxxxxxxx>
---
compat/mmap.c | 17 ++++-------------
1 files changed, 4 insertions(+), 13 deletions(-)
diff --git a/compat/mmap.c b/compat/mmap.c
index bb34c7e..98056f0 100644
--- a/compat/mmap.c
+++ b/compat/mmap.c
@@ -2,17 +2,11 @@
void *git_mmap(void *start, size_t length, int prot, int flags, int fd, off_t offset)
{
- int n = 0;
- off_t current_offset = lseek(fd, 0, SEEK_CUR);
+ size_t n = 0;
if (start != NULL || !(flags & MAP_PRIVATE))
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);
if (start == NULL) {
errno = ENOMEM;
@@ -20,7 +14,7 @@ void *git_mmap(void *start, size_t length, int prot, int flags, int fd, off_t of
}
while (n < length) {
- int count = read(fd, start+n, length-n);
+ ssize_t count = pread(fd, start + n, length - n, offset + n);
if (count == 0) {
memset(start+n, 0, length-n);
@@ -28,6 +22,8 @@ void *git_mmap(void *start, size_t length, int prot, int flags, int fd, off_t of
}
if (count < 0) {
+ if (errno == EAGAIN || errno == EINTR)
+ continue;
free(start);
errno = EACCES;
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;
}
- if (current_offset != lseek(fd, current_offset, SEEK_SET)) {
- errno = EINVAL;
- return MAP_FAILED;
- }
-
return start;
}
--
1.4.4.3.g2e63
-
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