[PATCH v2 02/20] safe_create_leading_directories(): set errno on SCLD_EXISTS

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

The exit path for SCLD_EXISTS wasn't setting errno, which some callers
use to generate error messages for the user. Fix the problem and
document that the function sets errno correctly to help avoid similar
regressions in the future.

While we're at it, document the difference between
safe_create_leading_directories() and
safe_create_leading_directories_const().

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
---
 cache.h     | 10 ++++++++--
 sha1_file.c |  4 +++-
 2 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/cache.h b/cache.h
index 26640b4..7d3f80c 100644
--- a/cache.h
+++ b/cache.h
@@ -950,8 +950,9 @@ int adjust_shared_perm(const char *path);
 
 /*
  * Create the directory containing the named path, using care to be
- * somewhat safe against races.  Return one of the scld_error values
- * to indicate success/failure.
+ * somewhat safe against races. Return one of the scld_error values to
+ * indicate success/failure. On error, set errno to describe the
+ * problem.
  *
  * SCLD_VANISHED indicates that one of the ancestor directories of the
  * path existed at one point during the function call and then
@@ -959,6 +960,11 @@ int adjust_shared_perm(const char *path);
  * directory while we were working.  To be robust against this kind of
  * race, callers might want to try invoking the function again when it
  * returns SCLD_VANISHED.
+ *
+ * The non _const version of this function temporarily modifies its
+ * path parameter while it is working but restores it before exiting.
+ * The _const version does not modify path (at the cost of having to
+ * make a temporary scratch copy).
  */
 enum scld_error {
 	SCLD_OK = 0,
diff --git a/sha1_file.c b/sha1_file.c
index 568120e..94c6779 100644
--- a/sha1_file.c
+++ b/sha1_file.c
@@ -135,8 +135,10 @@ enum scld_error safe_create_leading_directories(char *path)
 		*slash = '\0';
 		if (!stat(path, &st)) {
 			/* path exists */
-			if (!S_ISDIR(st.st_mode))
+			if (!S_ISDIR(st.st_mode)) {
+				errno = ENOTDIR;
 				ret = SCLD_EXISTS;
+			}
 		} else if (mkdir(path, 0777)) {
 			if (errno == EEXIST &&
 			    !stat(path, &st) && S_ISDIR(st.st_mode))
-- 
2.7.0