Merge branch 'mh/ref-races-optim-invalidate-cached'
[git/git.git] / refs.c
diff --git a/refs.c b/refs.c
index 038e5c7..a3f2302 100644 (file)
--- a/refs.c
+++ b/refs.c
@@ -1295,6 +1295,37 @@ static struct ref_entry *get_packed_ref(const char *refname)
        return find_ref(get_packed_refs(&ref_cache), refname);
 }
 
+/*
+ * A loose ref file doesn't exist; check for a packed ref.  The
+ * options are forwarded from resolve_safe_unsafe().
+ */
+static const char *handle_missing_loose_ref(const char *refname,
+                                           unsigned char *sha1,
+                                           int reading,
+                                           int *flag)
+{
+       struct ref_entry *entry;
+
+       /*
+        * The loose reference file does not exist; check for a packed
+        * reference.
+        */
+       entry = get_packed_ref(refname);
+       if (entry) {
+               hashcpy(sha1, entry->u.value.sha1);
+               if (flag)
+                       *flag |= REF_ISPACKED;
+               return refname;
+       }
+       /* The reference is not a packed reference, either. */
+       if (reading) {
+               return NULL;
+       } else {
+               hashclr(sha1);
+               return refname;
+       }
+}
+
 const char *resolve_ref_unsafe(const char *refname, unsigned char *sha1, int reading, int *flag)
 {
        int depth = MAXDEPTH;
@@ -1319,36 +1350,34 @@ const char *resolve_ref_unsafe(const char *refname, unsigned char *sha1, int rea
 
                git_snpath(path, sizeof(path), "%s", refname);
 
+               /*
+                * We might have to loop back here to avoid a race
+                * condition: first we lstat() the file, then we try
+                * to read it as a link or as a file.  But if somebody
+                * changes the type of the file (file <-> directory
+                * <-> symlink) between the lstat() and reading, then
+                * we don't want to report that as an error but rather
+                * try again starting with the lstat().
+                */
+       stat_ref:
                if (lstat(path, &st) < 0) {
-                       struct ref_entry *entry;
-
-                       if (errno != ENOENT)
+                       if (errno == ENOENT)
+                               return handle_missing_loose_ref(refname, sha1,
+                                                               reading, flag);
+                       else
                                return NULL;
-                       /*
-                        * The loose reference file does not exist;
-                        * check for a packed reference.
-                        */
-                       entry = get_packed_ref(refname);
-                       if (entry) {
-                               hashcpy(sha1, entry->u.value.sha1);
-                               if (flag)
-                                       *flag |= REF_ISPACKED;
-                               return refname;
-                       }
-                       /* The reference is not a packed reference, either. */
-                       if (reading) {
-                               return NULL;
-                       } else {
-                               hashclr(sha1);
-                               return refname;
-                       }
                }
 
                /* Follow "normalized" - ie "refs/.." symlinks by hand */
                if (S_ISLNK(st.st_mode)) {
                        len = readlink(path, buffer, sizeof(buffer)-1);
-                       if (len < 0)
-                               return NULL;
+                       if (len < 0) {
+                               if (errno == ENOENT || errno == EINVAL)
+                                       /* inconsistent with lstat; retry */
+                                       goto stat_ref;
+                               else
+                                       return NULL;
+                       }
                        buffer[len] = 0;
                        if (!prefixcmp(buffer, "refs/") &&
                                        !check_refname_format(buffer, 0)) {
@@ -1371,8 +1400,13 @@ const char *resolve_ref_unsafe(const char *refname, unsigned char *sha1, int rea
                 * a ref
                 */
                fd = open(path, O_RDONLY);
-               if (fd < 0)
-                       return NULL;
+               if (fd < 0) {
+                       if (errno == ENOENT)
+                               /* inconsistent with lstat; retry */
+                               goto stat_ref;
+                       else
+                               return NULL;
+               }
                len = read_in_full(fd, buffer, sizeof(buffer)-1);
                close(fd);
                if (len < 0)
@@ -1384,8 +1418,19 @@ const char *resolve_ref_unsafe(const char *refname, unsigned char *sha1, int rea
                /*
                 * Is it a symbolic ref?
                 */
-               if (prefixcmp(buffer, "ref:"))
-                       break;
+               if (prefixcmp(buffer, "ref:")) {
+                       /*
+                        * Please note that FETCH_HEAD has a second
+                        * line containing other data.
+                        */
+                       if (get_sha1_hex(buffer, sha1) ||
+                           (buffer[40] != '\0' && !isspace(buffer[40]))) {
+                               if (flag)
+                                       *flag |= REF_ISBROKEN;
+                               return NULL;
+                       }
+                       return refname;
+               }
                if (flag)
                        *flag |= REF_ISSYMREF;
                buf = buffer + 4;
@@ -1398,13 +1443,6 @@ const char *resolve_ref_unsafe(const char *refname, unsigned char *sha1, int rea
                }
                refname = strcpy(refname_buffer, buf);
        }
-       /* Please note that FETCH_HEAD has a second line containing other data. */
-       if (get_sha1_hex(buffer, sha1) || (buffer[40] != '\0' && !isspace(buffer[40]))) {
-               if (flag)
-                       *flag |= REF_ISBROKEN;
-               return NULL;
-       }
-       return refname;
 }
 
 char *resolve_refdup(const char *ref, unsigned char *sha1, int reading, int *flag)