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![Shawn O. Pearce](/assets/img/avatar_default.png)
There is a subtle (but important) linkage between receive-pack and index-pack that allows index-pack to create a packfile but protect it from being deleted by a concurrent `git repack -a -d` operation. The linkage works by having index-pack mark the newly created pack with a ".keep" file and then it passes the SHA-1 name of that new packfile to receive-pack along its stdout channel. The receive-pack process must unkeep the packfile by deleting the .keep file, but can it can only do so after all elgible refs have been updated in the receiving repository. This ensures that the packfile is either kept or its objects are reachable, preventing a concurrent repacker from deleting the packfile before it can determine that its objects are actually needed by the repository. The new builtin-fetch code needs to perform the same actions if it choose to run index-pack rather than unpack-objects, so I am moving this code out to its own function where both receive-pack and fetch-pack are able to invoke it when necessary. The caller is responsible for deleting the returned ".keep" and freeing the path if the returned path is not NULL. Signed-off-by: Shawn O. Pearce <spearce@spearce.org> Signed-off-by: Junio C Hamano <gitster@pobox.com>
208 lines
5.5 KiB
C
208 lines
5.5 KiB
C
#include "cache.h"
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#include "pack.h"
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#include "csum-file.h"
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uint32_t pack_idx_default_version = 1;
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uint32_t pack_idx_off32_limit = 0x7fffffff;
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static int sha1_compare(const void *_a, const void *_b)
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{
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struct pack_idx_entry *a = *(struct pack_idx_entry **)_a;
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struct pack_idx_entry *b = *(struct pack_idx_entry **)_b;
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return hashcmp(a->sha1, b->sha1);
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}
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/*
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* On entry *sha1 contains the pack content SHA1 hash, on exit it is
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* the SHA1 hash of sorted object names. The objects array passed in
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* will be sorted by SHA1 on exit.
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*/
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const char *write_idx_file(const char *index_name, struct pack_idx_entry **objects, int nr_objects, unsigned char *sha1)
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{
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struct sha1file *f;
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struct pack_idx_entry **sorted_by_sha, **list, **last;
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off_t last_obj_offset = 0;
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uint32_t array[256];
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int i, fd;
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SHA_CTX ctx;
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uint32_t index_version;
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if (nr_objects) {
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sorted_by_sha = objects;
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list = sorted_by_sha;
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last = sorted_by_sha + nr_objects;
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for (i = 0; i < nr_objects; ++i) {
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if (objects[i]->offset > last_obj_offset)
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last_obj_offset = objects[i]->offset;
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}
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qsort(sorted_by_sha, nr_objects, sizeof(sorted_by_sha[0]),
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sha1_compare);
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}
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else
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sorted_by_sha = list = last = NULL;
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if (!index_name) {
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static char tmpfile[PATH_MAX];
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snprintf(tmpfile, sizeof(tmpfile),
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"%s/tmp_idx_XXXXXX", get_object_directory());
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fd = xmkstemp(tmpfile);
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index_name = xstrdup(tmpfile);
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} else {
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unlink(index_name);
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fd = open(index_name, O_CREAT|O_EXCL|O_WRONLY, 0600);
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}
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if (fd < 0)
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die("unable to create %s: %s", index_name, strerror(errno));
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f = sha1fd(fd, index_name);
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/* if last object's offset is >= 2^31 we should use index V2 */
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index_version = (last_obj_offset >> 31) ? 2 : pack_idx_default_version;
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/* index versions 2 and above need a header */
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if (index_version >= 2) {
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struct pack_idx_header hdr;
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hdr.idx_signature = htonl(PACK_IDX_SIGNATURE);
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hdr.idx_version = htonl(index_version);
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sha1write(f, &hdr, sizeof(hdr));
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}
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/*
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* Write the first-level table (the list is sorted,
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* but we use a 256-entry lookup to be able to avoid
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* having to do eight extra binary search iterations).
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*/
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for (i = 0; i < 256; i++) {
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struct pack_idx_entry **next = list;
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while (next < last) {
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struct pack_idx_entry *obj = *next;
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if (obj->sha1[0] != i)
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break;
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next++;
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}
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array[i] = htonl(next - sorted_by_sha);
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list = next;
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}
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sha1write(f, array, 256 * 4);
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/* compute the SHA1 hash of sorted object names. */
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SHA1_Init(&ctx);
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/*
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* Write the actual SHA1 entries..
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*/
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list = sorted_by_sha;
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for (i = 0; i < nr_objects; i++) {
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struct pack_idx_entry *obj = *list++;
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if (index_version < 2) {
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uint32_t offset = htonl(obj->offset);
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sha1write(f, &offset, 4);
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}
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sha1write(f, obj->sha1, 20);
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SHA1_Update(&ctx, obj->sha1, 20);
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}
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if (index_version >= 2) {
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unsigned int nr_large_offset = 0;
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/* write the crc32 table */
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list = sorted_by_sha;
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for (i = 0; i < nr_objects; i++) {
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struct pack_idx_entry *obj = *list++;
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uint32_t crc32_val = htonl(obj->crc32);
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sha1write(f, &crc32_val, 4);
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}
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/* write the 32-bit offset table */
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list = sorted_by_sha;
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for (i = 0; i < nr_objects; i++) {
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struct pack_idx_entry *obj = *list++;
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uint32_t offset = (obj->offset <= pack_idx_off32_limit) ?
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obj->offset : (0x80000000 | nr_large_offset++);
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offset = htonl(offset);
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sha1write(f, &offset, 4);
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}
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/* write the large offset table */
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list = sorted_by_sha;
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while (nr_large_offset) {
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struct pack_idx_entry *obj = *list++;
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uint64_t offset = obj->offset;
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if (offset > pack_idx_off32_limit) {
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uint32_t split[2];
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split[0] = htonl(offset >> 32);
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split[1] = htonl(offset & 0xffffffff);
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sha1write(f, split, 8);
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nr_large_offset--;
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}
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}
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}
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sha1write(f, sha1, 20);
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sha1close(f, NULL, 1);
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SHA1_Final(sha1, &ctx);
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return index_name;
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}
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void fixup_pack_header_footer(int pack_fd,
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unsigned char *pack_file_sha1,
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const char *pack_name,
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uint32_t object_count)
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{
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static const int buf_sz = 128 * 1024;
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SHA_CTX c;
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struct pack_header hdr;
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char *buf;
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if (lseek(pack_fd, 0, SEEK_SET) != 0)
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die("Failed seeking to start: %s", strerror(errno));
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if (read_in_full(pack_fd, &hdr, sizeof(hdr)) != sizeof(hdr))
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die("Unable to reread header of %s: %s", pack_name, strerror(errno));
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if (lseek(pack_fd, 0, SEEK_SET) != 0)
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die("Failed seeking to start: %s", strerror(errno));
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hdr.hdr_entries = htonl(object_count);
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write_or_die(pack_fd, &hdr, sizeof(hdr));
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SHA1_Init(&c);
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SHA1_Update(&c, &hdr, sizeof(hdr));
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buf = xmalloc(buf_sz);
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for (;;) {
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ssize_t n = xread(pack_fd, buf, buf_sz);
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if (!n)
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break;
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if (n < 0)
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die("Failed to checksum %s: %s", pack_name, strerror(errno));
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SHA1_Update(&c, buf, n);
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}
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free(buf);
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SHA1_Final(pack_file_sha1, &c);
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write_or_die(pack_fd, pack_file_sha1, 20);
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}
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char *index_pack_lockfile(int ip_out)
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{
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int len, s;
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char packname[46];
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/*
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* The first thing we expects from index-pack's output
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* is "pack\t%40s\n" or "keep\t%40s\n" (46 bytes) where
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* %40s is the newly created pack SHA1 name. In the "keep"
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* case, we need it to remove the corresponding .keep file
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* later on. If we don't get that then tough luck with it.
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*/
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for (len = 0;
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len < 46 && (s = xread(ip_out, packname+len, 46-len)) > 0;
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len += s);
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if (len == 46 && packname[45] == '\n' &&
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memcmp(packname, "keep\t", 5) == 0) {
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char path[PATH_MAX];
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packname[45] = 0;
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snprintf(path, sizeof(path), "%s/pack/pack-%s.keep",
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get_object_directory(), packname + 5);
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return xstrdup(path);
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}
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return NULL;
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}
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