Re: Closing fds twice when using remote helpers
- Date: Wed, 15 May 2019 19:53:40 -0400
- From: Jeff King <peff@xxxxxxxx>
- Subject: Re: Closing fds twice when using remote helpers
On Thu, May 16, 2019 at 07:08:34AM +0900, Mike Hommey wrote:
> > >> - Except, well, fds being what they are, we in fact just closed a fd
> > >> from a packed_git->pack_fd. So, when use_pack is later called, and
> > >> tries to mmap data from that pack, it fails because the file
> > >> descriptor was closed.
> > Either dup() the file descriptor, or mmap() before you call the
> > consuming start_command().
If I understand your case correctly, the mmap() is not relevant. The
issue is that we close a random file descriptor accidentally, and it
just happens to be a pack descriptor later on. Right?
> You seem to imply this is my code doing something. It's not. The process
> that is doing all the things I noted above is an unmodified `git fetch`,
> when using a remote-helper transport. The use_pack happens after the
> transport is disposed because that's at the end of git fetch, when it
> updates refs.
Yes, it's a bug in git.
> Anyway, it would seem the fix is to dup(out) when passing it as in to
Generally, yes. It looks like maybe this spot?
diff --git a/transport-helper.c b/transport-helper.c
index fcd2a58d0e..45cdf891ec 100644
@@ -433,7 +433,7 @@ static int get_importer(struct transport *transport, struct child_process *fasti
struct helper_data *data = transport->data;
int cat_blob_fd, code;
- fastimport->in = helper->out;
+ fastimport->in = xdup(helper->out);
argv_array_push(&fastimport->args, debug ? "--stats" : "--quiet");
One thing I'd wonder, though: what is the contract between the helper
and fast-import here? In the current code, when the helper closes its
stdout, fast-import will see EOF. But not if we are holding on to
another copy of the descriptor.
In that case, the right solution is probably more like:
fastimport->in = helper->out;
helper->out = -1; /* hand ownership to fast-import */