[PATCH 5/8] Teach run_command how to setup a stdin pipe

[PATCH 5/8] Teach run_command how to setup a stdin pipe

[Shawn O. Pearce]

Sometimes callers trying to use run_command to execute a child
process will want to setup a pipe or file descriptor to redirect
into the child's stdin.

This idea is completely stolen from builtin-bundle's fork_with_pipe,
written by Johannes Schindelin.  All credit (and blame) should lie
with Dscho.  ;-)

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
---
 run-command.c |   35 ++++++++++++++++++++++++++++++++++-
 run-command.h |    3 +++
 2 files changed, 37 insertions(+), 1 deletions(-)

diff --git a/run-command.c b/run-command.c
index a866a06..03ff7bc 100644
--- a/run-command.c
+++ b/run-command.c
@@ -4,15 +4,39 @@
 
 int start_command(struct child_process *cmd)
 {
+	int need_in = !cmd->no_stdin && cmd->in < 0;
+	int fdin[2];
+
+	if (need_in) {
+		if (pipe(fdin) < 0)
+			return -ERR_RUN_COMMAND_PIPE;
+		cmd->in = fdin[1];
+		cmd->close_in = 1;
+	}
+
 	cmd->pid = fork();
-	if (cmd->pid < 0)
+	if (cmd->pid < 0) {
+		if (need_in) {
+			close(fdin[0]);
+			close(fdin[1]);
+		}
 		return -ERR_RUN_COMMAND_FORK;
+	}
+
 	if (!cmd->pid) {
 		if (cmd->no_stdin) {
 			int fd = open("/dev/null", O_RDWR);
 			dup2(fd, 0);
 			close(fd);
+		} else if (need_in) {
+			dup2(fdin[0], 0);
+			close(fdin[0]);
+			close(fdin[1]);
+		} else if (cmd->in) {
+			dup2(cmd->in, 0);
+			close(cmd->in);
 		}
+
 		if (cmd->stdout_to_stderr)
 			dup2(2, 1);
 		if (cmd->git_cmd) {
@@ -22,11 +46,20 @@ int start_command(struct child_process *cmd)
 		}
 		die("exec %s failed.", cmd->argv[0]);
 	}
+
+	if (need_in)
+		close(fdin[0]);
+	else if (cmd->in)
+		close(cmd->in);
+
 	return 0;
 }
 
 int finish_command(struct child_process *cmd)
 {
+	if (cmd->close_in)
+		close(cmd->in);
+
 	for (;;) {
 		int status, code;
 		pid_t waiting = waitpid(cmd->pid, &status, 0);
diff --git a/run-command.h b/run-command.h
index 24cdb4e..ff09067 100644
--- a/run-command.h
+++ b/run-command.h
@@ -4,6 +4,7 @@
 enum {
 	ERR_RUN_COMMAND_FORK = 10000,
 	ERR_RUN_COMMAND_EXEC,
+	ERR_RUN_COMMAND_PIPE,
 	ERR_RUN_COMMAND_WAITPID,
 	ERR_RUN_COMMAND_WAITPID_WRONG_PID,
 	ERR_RUN_COMMAND_WAITPID_SIGNAL,
@@ -13,6 +14,8 @@ enum {
 struct child_process {
 	const char **argv;
 	pid_t pid;
+	int in;
+	unsigned close_in:1;
 	unsigned no_stdin:1;
 	unsigned git_cmd:1; /* if this is to be git sub-command */
 	unsigned stdout_to_stderr:1;
-- 
1.5.0.3.942.g299f

Re: [PATCH 5/8] Teach run_command how to setup a stdin pipe

[Johannes Schindelin]

Hi,

On Sat, 10 Mar 2007, Shawn O. Pearce wrote:

> Sometimes callers trying to use run_command to execute a child process 
> will want to setup a pipe or file descriptor to redirect into the 
> child's stdin.
> 
> This idea is completely stolen from builtin-bundle's fork_with_pipe, 
> written by Johannes Schindelin.  All credit (and blame) should lie with 
> Dscho.  ;-)

;-)

Thank you for starting this thread. I think it makes a lot of sense in the 
face of the MinGW port. (I am not interested in the hook stuff personally, 
so I'll not comment on that.)

Ciao,
Dscho

Re: [PATCH 5/8] Teach run_command how to setup a stdin pipe

[Shawn O. Pearce]

Johannes Schindelin <Johannes.Schindelin@gmx.de> wrote:
> On Sat, 10 Mar 2007, Shawn O. Pearce wrote:
> 
> > Sometimes callers trying to use run_command to execute a child process 
> > will want to setup a pipe or file descriptor to redirect into the 
> > child's stdin.
> > 
> > This idea is completely stolen from builtin-bundle's fork_with_pipe, 
> > written by Johannes Schindelin.  All credit (and blame) should lie with 
> > Dscho.  ;-)
> 
> ;-)
> 
> Thank you for starting this thread. I think it makes a lot of sense in the 
> face of the MinGW port. (I am not interested in the hook stuff personally, 
> so I'll not comment on that.)

I'd like to see run_command learn how to also redirect stdout,
then replace fork_with_pipe in builtin-bundle with run_command.
We should be able to also improve some of our other more direct
uses of fork to use run_command at that point too.

I don't know squat about MinGW, so I don't know if having the
run_command abstraction really helps there or not, but I know we
tried to make it with the good intentions of being able to use it
to wrap that asinine CreateProcess() thing that Win32 has...

-- 
Shawn.

Re: [PATCH 5/8] Teach run_command how to setup a stdin pipe

[Johannes Schindelin]

Hi,

On Sat, 10 Mar 2007, Shawn O. Pearce wrote:

> Johannes Schindelin <Johannes.Schindelin@gmx.de> wrote:
> > On Sat, 10 Mar 2007, Shawn O. Pearce wrote:
> > 
> > > Sometimes callers trying to use run_command to execute a child 
> > > process will want to setup a pipe or file descriptor to redirect 
> > > into the child's stdin.
> > > 
> > > This idea is completely stolen from builtin-bundle's fork_with_pipe, 
> > > written by Johannes Schindelin.  All credit (and blame) should lie 
> > > with Dscho.  ;-)
> > 
> > ;-)
> > 
> > Thank you for starting this thread. I think it makes a lot of sense in 
> > the face of the MinGW port. (I am not interested in the hook stuff 
> > personally, so I'll not comment on that.)
> 
> I'd like to see run_command learn how to also redirect stdout, then 
> replace fork_with_pipe in builtin-bundle with run_command. We should be 
> able to also improve some of our other more direct uses of fork to use 
> run_command at that point too.

I concur.

> I don't know squat about MinGW, so I don't know if having the 
> run_command abstraction really helps there or not, but I know we tried 
> to make it with the good intentions of being able to use it to wrap that 
> asinine CreateProcess() thing that Win32 has...

There is only one place that I am aware of, where this is not enough: For 
the shallow thing, upload-pack fork()s but does not execute another 
program, but lists all the objects to be uploaded. (For shallow, this 
_cannot_ be an external process, since it mucks with the commits which are 
to be treated as shallow).

Ciao,
Dscho