Ephrim Khong <dr.khong@xxxxxxxxx> writes: > 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@xxxxxxxxx> > --- > 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. Interesting. It seems that this part of the code has always used O_TRUNC since its inception at 6d297f81 (Status update on merge-recursive in C, 2006-07-08) when two thieves smuggled it into our codebase. Back then, this was the only use of O_TRUNC|O_WRONLY|O_CREAT combination in the production codebase (as you observed, O_CREAT|O_EXCL|O_WRONLY was what all the other codepaths use). But the use of O_TRUNC has spread over time to other parts of the codebase, perhaps cargo culted. If you look at hits from $ git grep -e O_TRUNC -e O_EXCL you see the combination of CREAT/WRONLY/TRUNC used all over the place [*], especially in newer parts of the code. So it becomes very curious why this one location needs to be so special and you are not patching other uses of O_TRUNC. I do not think we mind fixing the use of O_TRUNC with "remove and then create with O_EXCL", but we'd probably want to * understand why only this place matters, or perhaps other uses of O_TRUNC needs the same fix to work "correctly" with your NFS mounts, in which case we'd need all of them addressed in the same series of patches, and * understand why your NFS mount is broken and give a better explanation as to why we need to have a workaround in our code. before doing so. Thanks. [Footnote] * It is understandable that CREAT/WRONLY/TRUNC are used in combination, as that is documented as a synonym for creat(). > 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));