terminal: log TIOCGPTPEER failure less alarmingly

This is not a fatal error and the fallback codepath is equally safe.
When we use TIOCGPTPEER we're using a stashed fd to the container's
devpts mount's ptmx device and allocating a new fd non-path based
through this ioctl. If this ioctl can't be used we're falling back to
allocating a pts device from the host's devpts mount's ptmx device which
is path-based but is not under control of the container and so that's
safe. The difference is just that the first method gets you a nice
native terminal with all the pleasantries of having tty and friends
working whereas the latter method does not.

Fixes: #3625
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

diff --git a/src/lxc/terminal.c b/src/lxc/terminal.c
index 029e36bbb6d537f7d0e00c98c04655a5a1e47f5c..6e1a2c2887295c65dc49a4dbe23854dd6f827e57 100644 (file)
--- a/src/lxc/terminal.c
+++ b/src/lxc/terminal.c
@@ -931,7 +931,17 @@ static int lxc_terminal_create_native(const char *name, const char *lxcpath, str
 
        terminal->pty = ioctl(terminal->ptx, TIOCGPTPEER, O_RDWR | O_NOCTTY | O_CLOEXEC);
        if (terminal->pty < 0) {
-               SYSWARN("Failed to allocate new pty device");
+               switch (errno) {
+               case ENOTTY:
+                       SYSTRACE("Pure fd-based terminal allocation not possible");
+                       break;
+               case ENOSPC:
+                       SYSTRACE("Exceeding number of allocatable terminals");
+                       break;
+               default:
+                       SYSWARN("Failed to allocate new pty device");
+                       break;
+               }
                goto err;
        }