[PATCH 19/33] refs: change how packed refs are deleted

[Michael Haggerty <mhagger@alum.mit.edu>]

Add a function remove_ref(), which removes a single entry from a
reference cache.

Use this function to reimplement repack_without_ref().  The old
version iterated over all refs, packing all of them except for the one
to be deleted, then discarded the entire packed reference cache.  The
new version deletes the doomed reference from the cache *before*
iterating.

This has two advantages:

* the code for writing packed-refs becomes simpler, because it doesn't
  have to exclude one of the references.

* it is no longer necessary to discard the packed refs cache after
  deleting a reference: symbolic refs cannot be packed, so packed
  references cannot depend on each other, so the rest of the packed
  refs cache remains valid after a reference is deleted.

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
---
 refs.c | 84 +++++++++++++++++++++++++++++++++++++++++++++++++++++-------------
 1 file changed, 68 insertions(+), 16 deletions(-)

diff --git a/refs.c b/refs.c
index 0c0668b..3c20853 100644
--- a/refs.c
+++ b/refs.c
@@ -467,6 +467,57 @@ static struct ref_entry *find_ref(struct ref_dir *dir, const char *refname)
 }
 
 /*
+ * Remove the entry with the given name from dir, recursing into
+ * subdirectories as necessary.  If refname is the name of a directory
+ * (i.e., ends with '/'), then remove the directory and its contents.
+ * If the removal was successful, return the number of entries
+ * remaining in the directory entry that contained the deleted entry.
+ * If the name was not found, return -1.  Please note that this
+ * function only deletes the entry from the cache; it does not delete
+ * it from the filesystem or ensure that other cache entries (which
+ * might be symbolic references to the removed entry) are updated.
+ * Nor does it remove any containing dir entries that might be made
+ * empty by the removal.  dir must represent the top-level directory
+ * and must already be complete.
+ */
+static int remove_entry(struct ref_dir *dir, const char *refname)
+{
+	int refname_len = strlen(refname);
+	int entry_index;
+	struct ref_entry *entry;
+	int is_dir = refname[refname_len - 1] == '/';
+	if (is_dir) {
+		/*
+		 * refname represents a reference directory.  Remove
+		 * the trailing slash; otherwise we will get the
+		 * directory *representing* refname rather than the
+		 * one *containing* it.
+		 */
+		char *dirname = xmemdupz(refname, refname_len - 1);
+		dir = find_containing_dir(dir, dirname, 0);
+		free(dirname);
+	} else {
+		dir = find_containing_dir(dir, refname, 0);
+	}
+	if (!dir)
+		return -1;
+	entry_index = search_ref_dir(dir, refname, refname_len);
+	if (entry_index == -1)
+		return -1;
+	entry = dir->entries[entry_index];
+
+	memmove(&dir->entries[entry_index],
+		&dir->entries[entry_index + 1],
+		(dir->nr - entry_index - 1) * sizeof(*dir->entries)
+		);
+	dir->nr--;
+	if (dir->sorted > entry_index)
+		dir->sorted--;
+	free_ref_entry(entry);
+	return dir->nr;
+}
+
+/*
  * Add a ref_entry to the ref_dir (unsorted), recursing into
  * subdirectories as necessary.  dir must represent the top-level
  * directory.  Return 0 on success.
@@ -1892,19 +1943,12 @@ struct ref_lock *lock_any_ref_for_update(const char *refname,
 	return lock_ref_sha1_basic(refname, old_sha1, flags, NULL);
 }
 
-struct repack_without_ref_sb {
-	const char *refname;
-	int fd;
-};
-
-static int repack_without_ref_fn(struct ref_entry *entry, void *cb_data)
+static int repack_ref_fn(struct ref_entry *entry, void *cb_data)
 {
-	struct repack_without_ref_sb *data = cb_data;
+	int *fd = cb_data;
 	char line[PATH_MAX + 100];
 	int len;
 
-	if (!strcmp(data->refname, entry->name))
-		return 0;
 	/* Silently skip broken refs: */
 	if (!ref_resolves_to_object(entry, 0))
 		return 0;
@@ -1913,7 +1957,7 @@ static int repack_without_ref_fn(struct ref_entry *entry, void *cb_data)
 	/* this should not happen but just being defensive */
 	if (len > sizeof(line))
 		die("too long a refname '%s'", entry->name);
-	write_or_die(data->fd, line, len);
+	write_or_die(*fd, line, len);
 	return 0;
 }
 
@@ -1921,22 +1965,30 @@ static struct lock_file packlock;
 
 static int repack_without_ref(const char *refname)
 {
-	struct repack_without_ref_sb data;
+	int fd;
 	struct ref_cache *refs = get_ref_cache(NULL);
 	struct ref_dir *packed;
 
 	if (!get_packed_ref(refname))
 		return 0; /* refname does not exist in packed refs */
 
-	data.refname = refname;
-	data.fd = hold_lock_file_for_update(&packlock, git_path("packed-refs"), 0);
-	if (data.fd < 0) {
+	fd = hold_lock_file_for_update(&packlock, git_path("packed-refs"), 0);
+	if (fd < 0) {
 		unable_to_lock_error(git_path("packed-refs"), errno);
 		return error("cannot delete '%s' from packed refs", refname);
 	}
 	clear_packed_ref_cache(refs);
 	packed = get_packed_refs(refs);
-	do_for_each_entry_in_dir(packed, 0, repack_without_ref_fn, &data);
+	/* Remove refname from the cache. */
+	if (remove_entry(packed, refname) == -1) {
+		/*
+		 * The packed entry disappeared while we were
+		 * acquiring the lock.
+		 */
+		rollback_lock_file(&packlock);
+		return 0;
+	}
+	do_for_each_entry_in_dir(packed, 0, repack_ref_fn, &fd);
 	return commit_lock_file(&packlock);
 }
 
@@ -1965,7 +2017,7 @@ int delete_ref(const char *refname, const unsigned char *sha1, int delopt)
 	ret |= repack_without_ref(lock->ref_name);
 
 	unlink_or_warn(git_path("logs/%s", lock->ref_name));
-	invalidate_ref_cache(NULL);
+	clear_loose_ref_cache(get_ref_cache(NULL));
 	unlock_ref(lock);
 	return ret;
 }
-- 
1.8.2.1