[PATCH 2/7] Switch git_mmap to use pread.
- From
Shawn O. Pearce <spearce@spearce.org>
- Date
- Dec 24, 2006, 05:45 UTC
- Message-ID
- <20061224054547.GB8146@spearce.org>
- In-Reply-To
- <487c7d0ea81f2f82f330e277e0aea38a66ca7cfe.1166939109.git.spearce@spearce.org>
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> --- 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