c/r: explicitly emit bind mounts as criu arguments

We switched to --ext-mount-map auto because of "system" (liblxc) added
mounts like the cgmanager socket that weren't in the config file. This had
the added advantage that we could drop all the mount processing code,
because we no longer needed an --ext-mount-map argument.

The problem here is that mounts can move between hosts. While
--ext-mount-map auto does its best to detect this situation, it explicitly
disallows moves that change the path name. In LXD, we bind mount
/var/lib/lxd/shmounts/$container to /dev/.lxd-mounts for each container,
and so when a container is renamed in a migration, the name changes.
--ext-mount-map auto won't detect this, and so the migration fails.

We *could* implement mount rewriting in CRIU, but my experience with cgroup
and apparmor rewriting is that this is painful and error prone. Instead, it
is much easier to go back to explicitly listing --ext-mount-map arguments
from the config file, and allow the source of the bind to change. We leave
--ext-mount-map auto to catch any stragling (or future) system added
mounts.

I believe this should fix Launchpad Bug 1580765

Signed-off-by: Tycho Andersen <tycho.andersen@canonical.com>

diff --git a/src/lxc/criu.c b/src/lxc/criu.c
index 094096777cb63b1cc4942a21882c4870641dd2b9..867139b67a5db9310d7d093fbfa1d54e3da1d423 100644 (file)
--- a/src/lxc/criu.c
+++ b/src/lxc/criu.c
@@ -46,6 +46,12 @@
 #include "network.h"
 #include "utils.h"
 
+#if IS_BIONIC
+#include <../include/lxcmntent.h>
+#else
+#include <mntent.h>
+#endif
+
 #define CRIU_VERSION           "2.0"
 
 #define CRIU_GITID_VERSION     "2.0"
@@ -123,6 +129,8 @@ static void exec_criu(struct criu_opts *opts)
        int static_args = 23, argc = 0, i, ret;
        int netnr = 0;
        struct lxc_list *it;
+       FILE *mnts;
+       struct mntent mntent;
 
        char buf[4096], tty_info[32];
        size_t pos;
@@ -200,6 +208,8 @@ static void exec_criu(struct criu_opts *opts)
        if (opts->user->action_script)
                static_args += 2;
 
+       static_args += 2 * lxc_list_len(&opts->c->lxc_conf->mount_list);
+
        ret = snprintf(log, PATH_MAX, "%s/%s.log", opts->user->directory, opts->action);
        if (ret < 0 || ret >= PATH_MAX) {
                ERROR("logfile name too long\n");
@@ -315,6 +325,36 @@ static void exec_criu(struct criu_opts *opts)
                DECLARE_ARG(opts->user->action_script);
        }
 
+       mnts = write_mount_file(&opts->c->lxc_conf->mount_list);
+       if (!mnts)
+               goto err;
+
+       while (getmntent_r(mnts, &mntent, buf, sizeof(buf))) {
+               char *fmt, *key, *val;
+               char arg[2 * PATH_MAX + 2];
+
+               if (strcmp(opts->action, "dump") == 0) {
+                       fmt = "/%s:%s";
+                       key = mntent.mnt_dir;
+                       val = mntent.mnt_dir;
+               } else {
+                       fmt = "%s:%s";
+                       key = mntent.mnt_dir;
+                       val = mntent.mnt_fsname;
+               }
+
+               ret = snprintf(arg, sizeof(arg), fmt, key, val);
+               if (ret < 0 || ret >= sizeof(arg)) {
+                       fclose(mnts);
+                       ERROR("snprintf failed");
+                       goto err;
+               }
+
+               DECLARE_ARG("--ext-mount-map");
+               DECLARE_ARG(arg);
+       }
+       fclose(mnts);
+
        if (strcmp(opts->action, "dump") == 0 || strcmp(opts->action, "pre-dump") == 0) {
                char pid[32], *freezer_relative;