Clean up sha1 file writing
- From
Linus Torvalds <torvalds@osdl.org>
- Date
- May 24, 2006, 15:30 UTC
- Message-ID
- <Pine.LNX.4.64.0605240820560.5623@g5.osdl.org>
This cleans up and future-proofs the sha1 file writing in sha1_file.c.
In particular, instead of doing a simple "write()" call and just verifying that it succeeds (or - as in one place - just assuming it does), it uses "write_buffer()" to write data to the file descriptor while correctly checking for partial writes, EINTR etc.
It also splits up write_sha1_to_fd() to be a lot more readable: if we need to re-create the compressed object, we do so in a separate helper function, making the logic a whole lot more modular and obvious.
Signed-off-by: Linus Torvalds <torvalds@osdl.org> ---
This shouldn't change any behaviour, and it's obviously touching some core code, so maybe it's not worth it. On the other hand, from a longer-term maintenance standpoint and from a "be much more careful when doing file writes" standpoint, I think it's worth it.
The re-write is "obviously correct" (famous last words) and is mostly just moving code around and getting rid of a few temporaries that become unnecessary as a result.
The patch looks a bit messy: the changes aren't actually that big, but the split-up and the resulting re-indentation makes the patch fairly unreadable, so the cleanups are more obvious when you look at the before-and-after side by side rather than when looking at the unified diff..)
diff --git a/sha1_file.c b/sha1_file.c index 2230010..c2fe7c2 100644 --- a/sha1_file.c +++ b/sha1_file.c @@ -1399,6 +1399,25 @@ int move_temp_to_file(const char *tmpfil return 0; } +static int write_buffer(int fd, const void *buf, size_t len) +{ + while (len) { + ssize_t size; + + size = write(fd, buf, len); + if (!size) + return error("file write: disk full"); + if (size < 0) { + if (errno == EINTR || errno == EAGAIN) + continue; + return error("file write error (%s)", strerror(errno)); + } + len -= size; + buf += size; + } + return 0; +} + int write_sha1_file(void *buf, unsigned long len, const char *type, unsigned char *returnsha1) { int size; @@ -1465,8 +1484,8 @@ int write_sha1_file(void *buf, unsigned deflateEnd(&stream); size = stream.total_out; - if (write(fd, compressed, size) != size) - die("unable to write file"); + if (write_buffer(fd, compressed, size) < 0) + die("unable to write sha1 file"); fchmod(fd, 0444); close(fd); free(compressed); @@ -1474,73 +1493,70 @@ int write_sha1_file(void *buf, unsigned return move_temp_to_file(tmpfile, filename); } -int write_sha1_to_fd(int fd, const unsigned char *sha1) +/* + * We need to unpack and recompress the object for writing + * it out to a different file. + */ +static void *repack_object(const unsigned char *sha1, unsigned long *objsize) { - ssize_t size; - unsigned long objsize; - int posn = 0; - void *map = map_sha1_file_internal(sha1, &objsize); - void *buf = map; - void *temp_obj = NULL; + size_t size; z_stream stream; + unsigned char *unpacked; + unsigned long len; + char type[20]; + char hdr[50]; + int hdrlen; + void *buf; - if (!buf) { - unsigned char *unpacked; - unsigned long len; - char type[20]; - char hdr[50]; - int hdrlen; - // need to unpack and recompress it by itself - unpacked = read_packed_sha1(sha1, type, &len); + // need to unpack and recompress it by itself + unpacked = read_packed_sha1(sha1, type, &len); - hdrlen = sprintf(hdr, "%s %lu", type, len) + 1; + hdrlen = sprintf(hdr, "%s %lu", type, len) + 1; - /* Set it up */ - memset(&stream, 0, sizeof(stream)); - deflateInit(&stream, Z_BEST_COMPRESSION); - size = deflateBound(&stream, len + hdrlen); - temp_obj = buf = xmalloc(size); + /* Set it up */ + memset(&stream, 0, sizeof(stream)); + deflateInit(&stream, Z_BEST_COMPRESSION); + size = deflateBound(&stream, len + hdrlen); + buf = xmalloc(size); - /* Compress it */ - stream.next_out = buf; - stream.avail_out = size; + /* Compress it */ + stream.next_out = buf; + stream.avail_out = size; - /* First header.. */ - stream.next_in = (void *)hdr; - stream.avail_in = hdrlen; - while (deflate(&stream, 0) == Z_OK) - /* nothing */; + /* First header.. */ + stream.next_in = (void *)hdr; + stream.avail_in = hdrlen; + while (deflate(&stream, 0) == Z_OK) + /* nothing */; - /* Then the data itself.. */ - stream.next_in = unpacked; - stream.avail_in = len; - while (deflate(&stream, Z_FINISH) == Z_OK) - /* nothing */; - deflateEnd(&stream); - free(unpacked); - - objsize = stream.total_out; - } + /* Then the data itself.. */ + stream.next_in = unpacked; + stream.avail_in = len; + while (deflate(&stream, Z_FINISH) == Z_OK) + /* nothing */; + deflateEnd(&stream); + free(unpacked); - do { - size = write(fd, buf + posn, objsize - posn); - if (size <= 0) { - if (!size) { - fprintf(stderr, "write closed\n"); - } else { - perror("write "); - } - return -1; - } - posn += size; - } while (posn < objsize); + *objsize = stream.total_out; + return buf; +} - if (map) - munmap(map, objsize); - if (temp_obj) - free(temp_obj); +int write_sha1_to_fd(int fd, const unsigned char *sha1) +{ + int retval; + unsigned long objsize; + void *buf = map_sha1_file_internal(sha1, &objsize); - return 0; + if (buf) { + retval = write_buffer(fd, buf, objsize); + munmap(buf, objsize); + return retval; + } + + buf = repack_object(sha1, &objsize); + retval = write_buffer(fd, buf, objsize); + free(buf); + return retval; } int write_sha1_from_fd(const unsigned char *sha1, int fd, char *buffer, @@ -1579,7 +1595,8 @@ int write_sha1_from_fd(const unsigned ch SHA1_Update(&c, discard, sizeof(discard) - stream.avail_out); } while (stream.avail_in && ret == Z_OK); - write(local, buffer, *bufposn - stream.avail_in); + if (write_buffer(local, buffer, *bufposn - stream.avail_in) < 0) + die("unable to write sha1 file"); memmove(buffer, buffer + *bufposn - stream.avail_in, stream.avail_in); *bufposn = stream.avail_in;