lxc-attach: error on -L/--pty-log + redirection

pty logging only works correctly when stdout and stderr refer to a pty. If they
do not, we do not dup2() them and lxc_console_cb_con() will never write to the
corresponding log file descriptor.

When redirection on stdout and stderr is used we can safely assume that the user
is already logging to a file or /dev/null and creating an additional pty log
doesn't seem to make sense.

Signed-off-by: Christian Brauner <christian.brauner@mailbox.org>

diff --git a/src/lxc/lxc_attach.c b/src/lxc/lxc_attach.c
index ed3ba0df057f3ecf6f098c2a387e3ae1239e37de..58f658bfdd06a63991ed533e777e3220a88f373b 100644 (file)
--- a/src/lxc/lxc_attach.c
+++ b/src/lxc/lxc_attach.c
@@ -21,7 +21,8 @@
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
-#define _GNU_SOURCE
+#include "config.h"
+
 #include <assert.h>
 #include <errno.h>
 #include <fcntl.h>
@@ -38,7 +39,6 @@
 #include "attach.h"
 #include "arguments.h"
 #include "caps.h"
-#include "config.h"
 #include "confile.h"
 #include "console.h"
 #include "log.h"
@@ -254,7 +254,7 @@ static int get_pty_on_host(struct lxc_container *c, struct wrapargs *wrap, int *
        INFO("Trying to allocate a pty on the host");
 
        if (!isatty(args->ptyfd)) {
-               ERROR("stdin is not a tty");
+               ERROR("Standard file descriptor does not refer to a pty\n.");
                return -1;
        }
 
@@ -324,28 +324,40 @@ err1:
        return ret;
 }
 
+static int stdfd_is_pty(void)
+{
+       if (isatty(STDIN_FILENO))
+               return STDIN_FILENO;
+       if (isatty(STDOUT_FILENO))
+               return STDOUT_FILENO;
+       if (isatty(STDERR_FILENO))
+               return STDERR_FILENO;
+
+       return -1;
+}
+
 int main(int argc, char *argv[])
 {
-       int ret = -1;
+       int ret = -1, r;
        int wexit = 0;
        pid_t pid;
        lxc_attach_options_t attach_options = LXC_ATTACH_OPTIONS_DEFAULT;
        lxc_attach_command_t command = (lxc_attach_command_t){.program = NULL};
 
-       ret = lxc_caps_init();
-       if (ret)
+       r = lxc_caps_init();
+       if (r)
                exit(EXIT_FAILURE);
 
-       ret = lxc_arguments_parse(&my_args, argc, argv);
-       if (ret)
+       r = lxc_arguments_parse(&my_args, argc, argv);
+       if (r)
                exit(EXIT_FAILURE);
 
        if (!my_args.log_file)
                my_args.log_file = "none";
 
-       ret = lxc_log_init(my_args.name, my_args.log_file, my_args.log_priority,
+       r = lxc_log_init(my_args.name, my_args.log_file, my_args.log_priority,
                           my_args.progname, my_args.quiet, my_args.lxcpath[0]);
-       if (ret)
+       if (r)
                exit(EXIT_FAILURE);
        lxc_log_options_no_override();
 
@@ -388,19 +400,23 @@ int main(int argc, char *argv[])
                command.argv = (char**)my_args.argv;
        }
 
-       if (isatty(STDIN_FILENO) || isatty(STDOUT_FILENO) || isatty(STDERR_FILENO)) {
-               struct wrapargs wrap = (struct wrapargs){
-                       .command = &command,
+       struct wrapargs wrap = (struct wrapargs){
+               .command = &command,
                        .options = &attach_options
-               };
-               if (isatty(STDIN_FILENO))
-                       wrap.ptyfd = STDIN_FILENO;
-               else if (isatty(STDOUT_FILENO))
-                       wrap.ptyfd = STDOUT_FILENO;
-               else if (isatty(STDERR_FILENO))
-                       wrap.ptyfd = STDERR_FILENO;
+       };
+
+       wrap.ptyfd = stdfd_is_pty();
+       if (wrap.ptyfd >= 0) {
+               if ((!isatty(STDOUT_FILENO) || !isatty(STDERR_FILENO)) && my_args.console_log) {
+                       fprintf(stderr, "-L/--pty-log can only be used when stdout and stderr refer to a pty.\n");
+                       goto out;
+               }
                ret = get_pty_on_host(c, &wrap, &pid);
        } else {
+               if (my_args.console_log) {
+                       fprintf(stderr, "-L/--pty-log can only be used when stdout and stderr refer to a pty.\n");
+                       goto out;
+               }
                if (command.program)
                        ret = c->attach(c, lxc_attach_run_command, &command, &attach_options, &pid);
                else