Making errno when returning from lock_file() meaningful, which should
fix

 * an existing almost-bug in lock_ref_sha1_basic where it assumes
   errno==ENOENT is meaningful and could waste some work on retries

 * an existing bug in repack_without_refs where it prints
   strerror(errno) and picks advice based on errno, despite errno
   potentially being zero and potentially having been clobbered by
   that point

Signed-off-by: Ronnie Sahlberg <sahlb...@google.com>
---
 lockfile.c | 17 ++++++++++++-----
 refs.c     |  1 +
 refs.h     |  1 +
 3 files changed, 14 insertions(+), 5 deletions(-)

diff --git a/lockfile.c b/lockfile.c
index 464031b..a921d77 100644
--- a/lockfile.c
+++ b/lockfile.c
@@ -121,7 +121,7 @@ static char *resolve_symlink(char *p, size_t s)
        return p;
 }
 
-
+/* Make sure errno contains a meaningful value on error */
 static int lock_file(struct lock_file *lk, const char *path, int flags)
 {
        /*
@@ -130,8 +130,10 @@ static int lock_file(struct lock_file *lk, const char 
*path, int flags)
         */
        static const size_t max_path_len = sizeof(lk->filename) - 5;
 
-       if (strlen(path) >= max_path_len)
+       if (strlen(path) >= max_path_len) {
+               errno = ENAMETOOLONG;
                return -1;
+       }
        strcpy(lk->filename, path);
        if (!(flags & LOCK_NODEREF))
                resolve_symlink(lk->filename, max_path_len);
@@ -148,9 +150,13 @@ static int lock_file(struct lock_file *lk, const char 
*path, int flags)
                        lock_file_list = lk;
                        lk->on_list = 1;
                }
-               if (adjust_shared_perm(lk->filename))
-                       return error("cannot fix permission bits on %s",
-                                    lk->filename);
+               if (adjust_shared_perm(lk->filename)) {
+                       int save_errno = errno;
+                       error("cannot fix permission bits on %s",
+                             lk->filename);
+                       errno = save_errno;
+                       return -1;
+               }
        }
        else
                lk->filename[0] = 0;
@@ -188,6 +194,7 @@ NORETURN void unable_to_lock_index_die(const char *path, 
int err)
        die("%s", buf.buf);
 }
 
+/* This should return a meaningful errno on failure */
 int hold_lock_file_for_update(struct lock_file *lk, const char *path, int 
flags)
 {
        int fd = lock_file(lk, path, flags);
diff --git a/refs.c b/refs.c
index 25c3a93..1e8f293 100644
--- a/refs.c
+++ b/refs.c
@@ -2184,6 +2184,7 @@ static int write_packed_entry_fn(struct ref_entry *entry, 
void *cb_data)
        return 0;
 }
 
+/* This should return a meaningful errno on failure */
 int lock_packed_refs(int flags)
 {
        struct packed_ref_cache *packed_ref_cache;
diff --git a/refs.h b/refs.h
index 94d4cd4..948cc53 100644
--- a/refs.h
+++ b/refs.h
@@ -81,6 +81,7 @@ extern void warn_dangling_symref(FILE *fp, const char 
*msg_fmt, const char *refn
 /*
  * Lock the packed-refs file for writing.  Flags is passed to
  * hold_lock_file_for_update().  Return 0 on success.
+ * Errno is set to something meaningful on error.
  */
 extern int lock_packed_refs(int flags);
 
-- 
2.0.0.282.g3799eda.dirty

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