run-command: support custom fd-set in async

This patch adds the possibility to supply a set of non-0 file
descriptors for async process communication instead of the
default-created pipe.

Additionally, we now support bi-directional communiction with the
async procedure, by giving the async function both read and write
file descriptors.

To retain compatiblity and similar "API feel" with start_command,
we require start_async callers to set .out = -1 to get a readable
file descriptor.  If either of .in or .out is 0, we supply no file
descriptor to the async process.

[sp: Note: Erik started this patch, and a huge bulk of it is
     his work.  All bugs were introduced later by Shawn.]

Signed-off-by: Erik Faye-Lund <kusmabite@gmail.com>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 4 insertions, 3 deletions

diff --git a/builtin-fetch-pack.c b/builtin-fetch-pack.c
index 8ed4a6feaa..dbd8b7bcc8 100644
--- a/builtin-fetch-pack.c
+++ b/builtin-fetch-pack.c
@@ -586,12 +586,12 @@ static int everything_local(struct ref **refs, int nr_match, char **match)
 	return retval;
 }
 
-static int sideband_demux(int fd, void *data)
+static int sideband_demux(int in, int out, void *data)
 {
 	int *xd = data;
 
-	int ret = recv_sideband("fetch-pack", xd[0], fd);
-	close(fd);
+	int ret = recv_sideband("fetch-pack", xd[0], out);
+	close(out);
 	return ret;
 }
 
@@ -613,6 +613,7 @@ static int get_pack(int xd[2], char **pack_lockfile)
 		 */
 		demux.proc = sideband_demux;
 		demux.data = xd;
+		demux.out = -1;
 		if (start_async(&demux))
 			die("fetch-pack: unable to fork off sideband"
 			    " demultiplexer");