lib/system: Add pb_run_cmd_pipe

Add a function to run a command and capture the output into a buffer.

Signed-off-by: Jeremy Kerr <jk@ozlabs.org>

2 files changed, 73 insertions, 2 deletions

diff --git a/lib/system/system.c b/lib/system/system.c
index dbdef46..7bb4997 100644
--- a/lib/system/system.c
+++ b/lib/system/system.c
@@ -102,6 +102,40 @@ int pb_rmdir_recursive(const char *base, const char *dir)
 	return 0;
 }
 
+static int read_pipe(void *ctx, int fd, char **bufp, int *lenp)
+{
+	int rc, len, alloc_len;
+	char *buf;
+
+	alloc_len = 4096;
+	len = 0;
+
+	buf = talloc_array(ctx, char, alloc_len);
+
+	for (;;) {
+		rc = read(fd, buf, alloc_len - len - 1);
+		if (rc <= 0)
+			break;
+
+		len += rc;
+		if (len == alloc_len - 1) {
+			alloc_len *= 2;
+			buf = talloc_realloc(ctx, buf, char, alloc_len);
+		}
+	}
+
+	if (rc < 0) {
+		talloc_free(buf);
+		return rc;
+	}
+
+	buf[len] = '\0';
+	*bufp = buf;
+	*lenp = len;
+
+	return 0;
+}
+
 /**
  * pb_run_cmd - Run the supplied command.
  * @cmd_argv: An argument list array for execv.
@@ -111,14 +145,24 @@ int pb_rmdir_recursive(const char *base, const char *dir)
 
 int pb_run_cmd(const char *const *cmd_argv, int wait, int dry_run)
 {
+	return pb_run_cmd_pipe(cmd_argv, wait, dry_run, NULL, NULL, NULL);
+}
+
+int pb_run_cmd_pipe(const char *const *cmd_argv, int wait, int dry_run,
+		void *ctx, char **stdout_buf, int *stdout_buf_len)
+{
 #if defined(DEBUG)
 	enum {do_debug = 1};
 #else
 	enum {do_debug = 0};
 #endif
-	int status;
+	int status, pipefd[2];
 	pid_t pid;
 
+	assert(!wait && stdout_buf);
+	assert(!!ctx != !!stdout_buf);
+	assert(!!stdout_buf != !!stdout_buf_len);
+
 	if (do_debug) {
 		const char *const *p = cmd_argv;
 
@@ -133,9 +177,22 @@ int pb_run_cmd(const char *const *cmd_argv, int wait, int dry_run)
 		pb_log("%s: %s%s\n", __func__, (dry_run ? "(dry-run) " : ""),
 			cmd_argv[0]);
 
+	if (stdout_buf) {
+		*stdout_buf = NULL;
+		*stdout_buf_len = 0;
+	}
+
 	if (dry_run)
 		return 0;
 
+	if (stdout_buf) {
+		status = pipe(pipefd);
+		if (status) {
+			pb_log("pipe failed");
+			return -1;
+		}
+	}
+
 	pid = fork();
 
 	if (pid == -1) {
@@ -143,12 +200,17 @@ int pb_run_cmd(const char *const *cmd_argv, int wait, int dry_run)
 		return -1;
 	}
 
+
 	if (pid == 0) {
 		int log = fileno(pb_log_get_stream());
 
 		/* Redirect child output to log. */
 
-		status = dup2(log, STDOUT_FILENO);
+		if (stdout_buf) {
+			status = dup2(pipefd[1], STDOUT_FILENO);
+		} else {
+			status = dup2(log, STDOUT_FILENO);
+		}
 		assert(status != -1);
 
 		status = dup2(log, STDERR_FILENO);
@@ -162,6 +224,13 @@ int pb_run_cmd(const char *const *cmd_argv, int wait, int dry_run)
 	if (!wait && !waitpid(pid, &status, WNOHANG))
 		return 0;
 
+	if (stdout_buf) {
+		close(pipefd[1]);
+		status = read_pipe(ctx, pipefd[0], stdout_buf, stdout_buf_len);
+		if (status)
+			return -1;
+	}
+
 	if (waitpid(pid, &status, 0) == -1) {
 		pb_log("%s: waitpid failed: %s\n", __func__,
 				strerror(errno));
diff --git a/lib/system/system.h b/lib/system/system.h
index 271c435..a7a1a12 100644
--- a/lib/system/system.h
+++ b/lib/system/system.h
@@ -18,6 +18,8 @@ struct pb_system_apps {
 extern const struct pb_system_apps pb_system_apps;
 
 int pb_run_cmd(const char *const *cmd_argv, int wait, int dry_run);
+int pb_run_cmd_pipe(const char *const *cmd_argv, int wait, int dry_run,
+		void *ctx, char **buf, int *buf_len);
 int pb_mkdir_recursive(const char *dir);
 int pb_rmdir_recursive(const char *base, const char *dir);