Have start_command() create a pipe to read the stderr of the child.

This adds another stanza that allocates a pipe that is connected to the
child's stderr and that the caller can read from. In order to request this
pipe, the caller sets cmd->err to -1.

The implementation is not exactly modeled after the stdout case: For stdout
the caller can supply an existing file descriptor, but this facility is
nowhere needed in the stderr case. Additionally, the caller is required to
close cmd->err.

Signed-off-by: Johannes Sixt <johannes.sixt@telecom.at>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

diff --git a/run-command.c b/run-command.c
index 7e779d33ee9ea5f7d2e6aedc8c3a0a0476e87135..d00c03bbdf6c699596e22cf7f08e8b6860a146a9 100644 (file)
--- a/run-command.c
+++ b/run-command.c
@@ -17,8 +17,8 @@ static inline void dup_devnull(int to)
 
 int start_command(struct child_process *cmd)
 {
-       int need_in, need_out;
-       int fdin[2], fdout[2];
+       int need_in, need_out, need_err;
+       int fdin[2], fdout[2], fderr[2];
 
        need_in = !cmd->no_stdin && cmd->in < 0;
        if (need_in) {
@@ -41,12 +41,26 @@ int start_command(struct child_process *cmd)
                cmd->close_out = 1;
        }
 
+       need_err = cmd->err < 0;
+       if (need_err) {
+               if (pipe(fderr) < 0) {
+                       if (need_in)
+                               close_pair(fdin);
+                       if (need_out)
+                               close_pair(fdout);
+                       return -ERR_RUN_COMMAND_PIPE;
+               }
+               cmd->err = fderr[0];
+       }
+
        cmd->pid = fork();
        if (cmd->pid < 0) {
                if (need_in)
                        close_pair(fdin);
                if (need_out)
                        close_pair(fdout);
+               if (need_err)
+                       close_pair(fderr);
                return -ERR_RUN_COMMAND_FORK;
        }
 
@@ -73,6 +87,11 @@ int start_command(struct child_process *cmd)
                        close(cmd->out);
                }
 
+               if (need_err) {
+                       dup2(fderr[1], 2);
+                       close_pair(fderr);
+               }
+
                if (cmd->dir && chdir(cmd->dir))
                        die("exec %s: cd to %s failed (%s)", cmd->argv[0],
                            cmd->dir, strerror(errno));
@@ -102,6 +121,9 @@ int start_command(struct child_process *cmd)
        else if (cmd->out > 1)
                close(cmd->out);
 
+       if (need_err)
+               close(fderr[1]);
+
        return 0;
 }
 

diff --git a/run-command.h b/run-command.h
index 7958eb1e0b7a927019460e06d7a01622eddf81df..35b9fb61f17e6b178f76c05ccd761b4a34c661bf 100644 (file)
--- a/run-command.h
+++ b/run-command.h
@@ -16,6 +16,7 @@ struct child_process {
        pid_t pid;
        int in;
        int out;
+       int err;
        const char *dir;
        const char *const *env;
        unsigned close_in:1;