conf: attach devpts mount directly when new mount api can be used

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

diff --git a/src/lxc/conf.c b/src/lxc/conf.c
index 74da508d889a3e8dc43a3dbcc6b124a8797608f7..d5f40f6fd580502b30cb4c143ba812434688ed24 100644 (file)
--- a/src/lxc/conf.c
+++ b/src/lxc/conf.c
@@ -1667,14 +1667,27 @@ static int lxc_prepare_devpts_child(struct lxc_handler *handler)
 {
        __do_close int fd_fs = -EBADF, fd_fsmnt = -EBADF;
        struct lxc_conf *conf = handler->conf;
+       struct lxc_rootfs *rootfs = &conf->rootfs;
        int ret;
 
-       if (!can_use_mount_api())
-               return 0;
-
        if (conf->pty_max <= 0)
                return log_debug(0, "No new devpts instance will be mounted since no pts devices are requested");
 
+       ret = strnprintf(rootfs->buf, sizeof(rootfs->buf),
+                        "/proc/self/fd/%d/pts", rootfs->dfd_dev);
+       if (ret < 0)
+               return syserror("Failed to create path");
+
+       (void)umount2(rootfs->buf, MNT_DETACH);
+
+       /* Create mountpoint for devpts instance. */
+       ret = mkdirat(rootfs->dfd_dev, "pts", 0755);
+       if (ret < 0 && errno != EEXIST)
+               return log_error_errno(-1, errno, "Failed to create \"/dev/pts\" directory");
+
+       if (!can_use_mount_api())
+               return 0;
+
        fd_fs = fs_prepare("devpts", -EBADF, "", 0, 0);
        if (fd_fs < 0)
                return syserror("Failed to prepare filesystem context for devpts");
@@ -1710,10 +1723,14 @@ static int lxc_prepare_devpts_child(struct lxc_handler *handler)
        fd_fsmnt = fsmount(fd_fs, FSMOUNT_CLOEXEC, MOUNT_ATTR_NOSUID | MOUNT_ATTR_NOEXEC);
        if (fd_fsmnt < 0)
                return syserror("Failed to create new mount for filesystem context %d", fd_fs);
-
        TRACE("Created detached devpts mount %d", fd_fsmnt);
-       handler->conf->devpts_fd = move_fd(fd_fsmnt);
 
+       ret = move_mount(fd_fsmnt, "", rootfs->dfd_dev, "pts", MOVE_MOUNT_F_EMPTY_PATH);
+       if (ret)
+               return syserror("Failed to attach devpts mount %d to %d/pts", conf->devpts_fd, rootfs->dfd_dev);
+
+       DEBUG("Attached detached devpts mount %d to %d/pts", fd_fsmnt, rootfs->dfd_dev);
+       handler->conf->devpts_fd = move_fd(fd_fsmnt);
        return 0;
 }
 
@@ -1730,19 +1747,14 @@ static int lxc_finalize_devpts_child(struct lxc_handler *handler)
        if (conf->pty_max <= 0)
                return log_debug(0, "No new devpts instance will be mounted since no pts devices are requested");
 
-       /*
-        * Fallback codepath in case the new mount API can't be used to create
-        * detached mounts.
-        */
-       if (conf->devpts_fd >= 0) {
-               ret = move_mount(conf->devpts_fd, "", rootfs->dfd_dev, "pts", MOVE_MOUNT_F_EMPTY_PATH);
-               if (ret)
-                       return syserror("Failed to attach devpts mount %d to %d/pts", conf->devpts_fd, rootfs->dfd_dev);
-
-               DEBUG("Attached detached devpts mount %d to %d/pts", conf->devpts_fd, rootfs->dfd_dev);
-       } else {
+       if (!can_use_mount_api()) {
                __do_close int devpts_fd = -EBADF;
 
+               /*
+                * Fallback codepath in case the new mount API can't be used to
+                * create detached mounts.
+                */
+
                ret = strnprintf(devpts_mntopts, sizeof(devpts_mntopts), "%s,max=%zu",
                                default_devpts_mntopts, conf->pty_max);
                if (ret < 0)
@@ -1776,7 +1788,6 @@ static int lxc_finalize_devpts_child(struct lxc_handler *handler)
                        if (ret == 0)
                                break;
                }
-
                if (ret < 0)
                        return log_error_errno(-1, errno, "Failed to mount new devpts instance");