[RFC PATCH] merge-recursive: create new files with O_EXCL

[Ephrim Khong <dr.khong@gmail.com>]

When re-writing the content of a file during a merge, the file
is first unlinked and then re-created. Since it is a new file
at the time of the open call, O_EXCL should be passed to clarify
that the file is expected to be new.

Signed-off-by: Ephrim Khong <dr.khong@gmail.com>
---
This is actually a fix for an issue we ran into on an nfs4
mount. Files created with O_TRUNC instead of O_EXCL sometimes
had their permissions wrong. However, it appears to be a safe
thing to change this, especially since other parts of the
git codebase also prefer the O_EXCL flag.

 merge-recursive.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/merge-recursive.c b/merge-recursive.c
index f736a0f632..f72a376c5b 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -974,7 +974,7 @@ static int update_file_flags(struct merge_options *opt,
 			int fd;
 			int mode = (contents->mode & 0100 ? 0777 : 0666);

-			fd = open(path, O_WRONLY | O_TRUNC | O_CREAT, mode);
+			fd = open(path, O_WRONLY | O_EXCL | O_CREAT, mode);
 			if (fd < 0) {
 				ret = err(opt, _("failed to open '%s': %s"),
 					  path, strerror(errno));
-- 
2.30.1.1.g07d5ea6f42.dirty