Refactor index-pack "keep $sha1" handling for reuse

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>

diff --git a/pack-write.c b/pack-write.c
index e59b197e5ebb301107f9a18b7765e18097a1c8e3..979bdfff7c516ada7fb36281a22b41d303d1b99c 100644 (file)
--- a/pack-write.c
+++ b/pack-write.c
@@ -179,3 +179,29 @@ void fixup_pack_header_footer(int pack_fd,
        SHA1_Final(pack_file_sha1, &c);
        write_or_die(pack_fd, pack_file_sha1, 20);
 }
+
+char *index_pack_lockfile(int ip_out)
+{
+       int len, s;
+       char packname[46];
+
+       /*
+        * The first thing we expects from index-pack's output
+        * is "pack\t%40s\n" or "keep\t%40s\n" (46 bytes) where
+        * %40s is the newly created pack SHA1 name.  In the "keep"
+        * case, we need it to remove the corresponding .keep file
+        * later on.  If we don't get that then tough luck with it.
+        */
+       for (len = 0;
+                len < 46 && (s = xread(ip_out, packname+len, 46-len)) > 0;
+                len += s);
+       if (len == 46 && packname[45] == '\n' &&
+               memcmp(packname, "keep\t", 5) == 0) {
+               char path[PATH_MAX];
+               packname[45] = 0;
+               snprintf(path, sizeof(path), "%s/pack/pack-%s.keep",
+                        get_object_directory(), packname + 5);
+               return xstrdup(path);
+       }
+       return NULL;
+}

diff --git a/pack.h b/pack.h
index f357c9f4282d5bc8bbcff6f3a44b9812415745a6..b57ba2d9ed6120612c2576b07d8c185d4b54bb76 100644 (file)
--- a/pack.h
+++ b/pack.h
@@ -59,6 +59,7 @@ extern const char *write_idx_file(const char *index_name, struct pack_idx_entry
 
 extern int verify_pack(struct packed_git *, int);
 extern void fixup_pack_header_footer(int, unsigned char *, const char *, uint32_t);
+extern char *index_pack_lockfile(int fd);
 
 #define PH_ERROR_EOF           (-1)
 #define PH_ERROR_PACK_SIGNATURE        (-2)

diff --git a/receive-pack.c b/receive-pack.c
index d3c422be58c5ee1af7e75cf4186bc9bbfb19ec30..61e9929763133e9dbfb17b9c3097b2149b4fade0 100644 (file)
--- a/receive-pack.c
+++ b/receive-pack.c
@@ -382,9 +382,8 @@ static const char *unpack(void)
                }
        } else {
                const char *keeper[6];
-               int s, len, status;
+               int s, status;
                char keep_arg[256];
-               char packname[46];
                struct child_process ip;
 
                s = sprintf(keep_arg, "--keep=receive-pack %i on ", getpid());
@@ -403,26 +402,7 @@ static const char *unpack(void)
                ip.git_cmd = 1;
                if (start_command(&ip))
                        return "index-pack fork failed";
-
-               /*
-                * The first thing we expects from index-pack's output
-                * is "pack\t%40s\n" or "keep\t%40s\n" (46 bytes) where
-                * %40s is the newly created pack SHA1 name.  In the "keep"
-                * case, we need it to remove the corresponding .keep file
-                * later on.  If we don't get that then tough luck with it.
-                */
-               for (len = 0;
-                    len < 46 && (s = xread(ip.out, packname+len, 46-len)) > 0;
-                    len += s);
-               if (len == 46 && packname[45] == '\n' &&
-                   memcmp(packname, "keep\t", 5) == 0) {
-                       char path[PATH_MAX];
-                       packname[45] = 0;
-                       snprintf(path, sizeof(path), "%s/pack/pack-%s.keep",
-                                get_object_directory(), packname + 5);
-                       pack_lockfile = xstrdup(path);
-               }
-
+               pack_lockfile = index_pack_lockfile(ip.out);
                status = finish_command(&ip);
                if (!status) {
                        reprepare_packed_git();