Re: [PATCH v4 03/16] index-helper: new daemon for caching index and related stuff

On Fri, 2016-04-15 at 17:04 -0700, Stefan Beller wrote:

quoted

+static int try_shm(struct index_state *istate)
+{
+       void *new_mmap = NULL;
+       size_t old_size = istate->mmap_size;
+       ssize_t new_size;
+       const unsigned char *sha1;
+       struct stat st;
+       int fd;
+
+       if (!is_main_index(istate) ||
+           old_size <= 20 ||
+           stat(git_path("index-helper.path"), &st))
+               return -1;
+       if (poke_daemon(istate, &st, 0))
+               return -1;
+       sha1 = (unsigned char *)istate->mmap + old_size - 20;
+
+       fd = open(index_helper_path("git-index-%s",
sha1_to_hex(sha1)),
+                 O_RDONLY);
+       if (fd < 0)
+               goto fail;
+
+       if (fstat(fd, &st))
+               goto fail;
+
+       new_size = st.st_size;
+       new_mmap = mmap(NULL, new_size, PROT_READ, MAP_SHARED, fd,
0);
+       if (new_size <= 20 ||
+           hashcmp((unsigned char *)istate->mmap + old_size - 20,
+                   (unsigned char *)new_mmap + new_size - 20)) {
+               if (new_mmap)
+                       munmap(new_mmap, new_size);
+               goto fail;

coming from here

quoted

+       }
+
+       /* The memory barrier here matches index
-helper.c:share_index. */
+       __sync_synchronize();
+
+       munmap(istate->mmap, istate->mmap_size);
+       istate->mmap = new_mmap;
+       istate->mmap_size = new_size;
+       istate->from_shm = 1;
+       return 0;
+
+fail:

fd may be leaking here?

quoted

+       poke_daemon(istate, &st, 1);
+       return -1;
+}
+

Good point.  (It's also leaking on the happy path -- will fix all of
those)