[PATCH v3 2/2] setup: don't fail if commondir reference is deleted.

[Michal Suchanek <msuchanek@suse.de>]

Apparently it can happen that stat() claims there is a commondir file but when
trying to open the file it is missing.

Another even rarer issue is that the file might be zero size because another
process initializing a worktree opened the file but has not written is content
yet.

When any of this happnes git aborts failing to perform perfectly valid
command because unrelated worktree is not yet fully initialized.

Rather than testing if the file exists before reading it handle ENOENT
and ENOTDIR.

Signed-off-by: Michal Suchanek <msuchanek@suse.de>
---
v2:
- do not test file existence first, just read it and handle ENOENT.
- handle zero size file correctly
v3:
- handle ENOTDIR as well
- add more details to commit message
---
 setup.c | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/setup.c b/setup.c
index ca9e8a949ed8..49306e36990d 100644
--- a/setup.c
+++ b/setup.c
@@ -270,12 +270,20 @@ int get_common_dir_noenv(struct strbuf *sb, const char *gitdir)
 {
 	struct strbuf data = STRBUF_INIT;
 	struct strbuf path = STRBUF_INIT;
-	int ret = 0;
+	int ret;
 
 	strbuf_addf(&path, "%s/commondir", gitdir);
-	if (file_exists(path.buf)) {
-		if (strbuf_read_file(&data, path.buf, 0) <= 0)
+	ret = strbuf_read_file(&data, path.buf, 0);
+	if (ret <= 0) {
+		/*
+		 * if file is missing or zero size (just being written)
+		 * assume default, bail otherwise
+		 */
+		if (ret && errno != ENOENT && errno != ENOTDIR)
 			die_errno(_("failed to read %s"), path.buf);
+		strbuf_addstr(sb, gitdir);
+		ret = 0;
+	} else {
 		while (data.len && (data.buf[data.len - 1] == '\n' ||
 				    data.buf[data.len - 1] == '\r'))
 			data.len--;
@@ -286,8 +294,6 @@ int get_common_dir_noenv(struct strbuf *sb, const char *gitdir)
 		strbuf_addbuf(&path, &data);
 		strbuf_add_real_path(sb, path.buf);
 		ret = 1;
-	} else {
-		strbuf_addstr(sb, gitdir);
 	}
 
 	strbuf_release(&data);
-- 
2.20.1