util: added samba_runcmd()

This allows us to run a child command in an async fashion, with
control over logging of stdout and stderr (which appears in the Samba
log file). This is useful for ensuring we don't miss important
messages from rndc commands (for example).

Pair-Programmed-With: Andrew Bartlett <abartlet@samba.org>

1 files changed, 253 insertions, 0 deletions

diff --git a/lib/util/util_runcmd.c b/lib/util/util_runcmd.c
new file mode 100644
index 0000000000..80574c4400
--- /dev/null
+++ b/lib/util/util_runcmd.c
@@ -0,0 +1,253 @@
+/*
+   Unix SMB/CIFS mplementation.
+
+   run a child command
+
+   Copyright (C) Andrew Tridgell 2010
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+*/
+
+/*
+  this runs a child command with stdout and stderr going to the Samba
+  log
+ */
+
+#include "includes.h"
+#include "system/filesys.h"
+#include "lib/tevent/tevent.h"
+#include "libcli/composite/composite.h"
+
+struct samba_runcmd {
+	int stdout_log_level;
+	int stderr_log_level;
+	struct tevent_fd *fde_stdout;
+	struct tevent_fd *fde_stderr;
+	int fd_stdout, fd_stderr;
+	char *arg0;
+	pid_t pid;
+	char buf[1024];
+	uint16_t buf_used;
+};
+
+/*
+  called when a command times out
+ */
+static void runcmd_timeout(struct tevent_context *ev,
+			   struct tevent_timer *te,
+			   struct timeval current_time,
+			   void *private_data)
+{
+	struct composite_context *c = talloc_get_type_abort(private_data, struct composite_context);
+	struct samba_runcmd *r = talloc_get_type_abort(c->private_data, struct samba_runcmd);
+	kill(r->pid, SIGKILL);
+	waitpid(r->pid, NULL, 0);
+	talloc_free(r->fde_stderr);
+	talloc_free(r->fde_stdout);
+	composite_error(c, NT_STATUS_IO_TIMEOUT);
+}
+
+/*
+  handle stdout/stderr from the child
+ */
+static void runcmd_io_handler(struct tevent_context *ev,
+			      struct tevent_fd *fde,
+			      uint16_t flags,
+			      void *private_data)
+{
+	struct composite_context *c = talloc_get_type_abort(private_data, struct composite_context);
+	struct samba_runcmd *r = talloc_get_type_abort(c->private_data, struct samba_runcmd);
+	int level;
+	char *p;
+	int n, fd;
+
+	if (fde == r->fde_stdout) {
+		level = r->stdout_log_level;
+		fd = r->fd_stdout;
+	} else {
+		level = r->stderr_log_level;
+		fd = r->fd_stderr;
+	}
+
+	if (!(flags & TEVENT_FD_READ)) {
+		return;
+	}
+
+	n = read(fd, &r->buf[r->buf_used],
+		 sizeof(r->buf) - r->buf_used);
+	if (n > 0) {
+		r->buf_used += n;
+	} else if (n == 0) {
+		if (fde == r->fde_stdout) {
+			talloc_free(fde);
+			r->fde_stdout = NULL;
+		}
+		if (fde == r->fde_stderr) {
+			talloc_free(fde);
+			r->fde_stderr = NULL;
+		}
+		if (r->fde_stdout == NULL &&
+		    r->fde_stderr == NULL) {
+			int status;
+			/* the child has closed both stdout and
+			 * stderr, assume its dead */
+			pid_t pid = waitpid(r->pid, &status, 0);
+			if (pid != r->pid) {
+				DEBUG(0,("Error in waitpid() for child %s\n", r->arg0));
+				composite_error(c, map_nt_error_from_unix(errno));
+				return;
+			}
+			status = WEXITSTATUS(status);
+			DEBUG(3,("Child %s exited with status %d\n", r->arg0, status));
+			if (status == 0) {
+				composite_done(c);
+			} else {
+				composite_error(c, map_nt_error_from_unix(status));
+			}
+			return;
+		}
+		return;
+	}
+
+	while (r->buf_used > 0 &&
+	       (p = memchr(r->buf, '\n', r->buf_used)) != NULL) {
+		int n1 = (p - r->buf)+1;
+		int n2 = n1 - 1;
+		/* swallow \r from child processes */
+		if (n2 > 0 && r->buf[n2-1] == '\r') {
+			n2--;
+		}
+		DEBUG(level,("%s: %*.*s\n", r->arg0, n2, n2, r->buf));
+		memmove(r->buf, p+1, sizeof(r->buf) - n1);
+		r->buf_used -= n1;
+	}
+
+	/* the buffer could have completely filled - unfortunately we have
+	   no choice but to dump it out straight away */
+	if (r->buf_used == sizeof(r->buf)) {
+		DEBUG(level,("%s: %*.*s\n", r->arg0, r->buf_used, r->buf_used, r->buf));
+		r->buf_used = 0;
+	}
+}
+
+
+/*
+  run a command as a child process, with a timeout.
+
+  any stdout/stderr from the child will appear in the Samba logs with
+  the specified log levels
+ */
+struct composite_context *samba_runcmd(struct tevent_context *ev,
+				       TALLOC_CTX *mem_ctx,
+				       struct timeval timeout,
+				       int stdout_log_level,
+				       int stderr_log_level,
+				       const char *arg0, ...)
+{
+	struct samba_runcmd *r;
+	int p1[2], p2[2];
+	char **argv;
+	int ret;
+	va_list ap;
+	struct composite_context *c;
+
+	c = composite_create(mem_ctx, ev);
+	if (c == NULL) return NULL;
+
+	r = talloc_zero(c, struct samba_runcmd);
+	if (composite_nomem(r, c)) return c;
+
+	c->private_data = r;
+
+	r->stdout_log_level = stdout_log_level;
+	r->stderr_log_level = stderr_log_level;
+
+	r->arg0 = talloc_strdup(r, arg0);
+	if (composite_nomem(r->arg0, c)) return c;
+
+	if (pipe(p1) != 0) {
+		composite_error(c, map_nt_error_from_unix(errno));
+		return c;
+	}
+	if (pipe(p2) != 0) {
+		composite_error(c, map_nt_error_from_unix(errno));
+		close(p1[0]);
+		close(p1[1]);
+		return c;
+	}
+
+	r->pid = fork();
+	if (r->pid == (pid_t)-1) {
+		composite_error(c, map_nt_error_from_unix(errno));
+		close(p1[0]);
+		close(p1[1]);
+		close(p2[0]);
+		close(p2[1]);
+		return c;
+	}
+
+	if (r->pid != 0) {
+		/* the parent */
+		close(p1[1]);
+		close(p2[1]);
+		r->fd_stdout = p1[0];
+		r->fd_stderr = p2[0];
+		set_blocking(r->fd_stdout, false);
+		set_blocking(r->fd_stderr, false);
+		r->fde_stdout = tevent_add_fd(ev, r, r->fd_stdout, TEVENT_FD_READ, runcmd_io_handler, c);
+		tevent_fd_set_auto_close(r->fde_stdout);
+		r->fde_stderr = tevent_add_fd(ev, r, r->fd_stderr, TEVENT_FD_READ, runcmd_io_handler, c);
+		tevent_fd_set_auto_close(r->fde_stderr);
+		if (!timeval_is_zero(&timeout)) {
+			tevent_add_timer(ev, r, timeout, runcmd_timeout, c);
+		}
+		return c;
+	}
+
+	/* the child */
+	close(p1[0]);
+	close(p2[0]);
+	close(0);
+	close(1);
+	close(2);
+
+	/* setup for logging to go to the parents debug log */
+	open("/dev/null", O_RDONLY); /* for stdin */
+	dup2(p1[1], 1);
+	dup2(p2[1], 2);
+
+	argv = str_list_make_single(r, r->arg0);
+	if (!argv) {
+		fprintf(stderr, "Out of memory in child\n");
+		_exit(255);
+	}
+
+	va_start(ap, arg0);
+	while (1) {
+		char *arg = va_arg(ap, char *);
+		if (arg == NULL) break;
+		argv = discard_const_p(char *, str_list_add((const char **)argv, arg));
+		if (!argv) {
+			fprintf(stderr, "Out of memory in child\n");
+			_exit(255);
+		}
+	}
+	va_end(ap);
+
+	ret = execv(arg0, argv);
+	fprintf(stderr, "Failed to exec child - %s\n", strerror(errno));
+	_exit(255);
+	return NULL;
+}