[CRIU] [PATCH v4 3/3] mount: Restore binfmt_misc content in case of missing mount

[Kirill Tkhai]

In case of mount image is not containing binfmt_misc mountpoint,
scan image directory for binfmt_misc content file (binfmt-misc-xxx).
If a file is found, add temporary mountpoint to mount tree and
restore the content in ordinary way. Then, umount temporary mountpoint.

v4: New

Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>
---
 criu/mount.c |   61 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 59 insertions(+), 2 deletions(-)

diff --git a/criu/mount.c b/criu/mount.c
index d583429..8657c36 100644
--- a/criu/mount.c
+++ b/criu/mount.c
@@ -1379,6 +1379,39 @@ static int try_mount_binfmt_misc(struct ns_id *ns, unsigned int *s_dev)
 	return ret ? -1 : exit_code;
 }
 
+static int find_binfmt_misc_img(unsigned int *s_dev)
+{
+	struct dirent *de;
+	int dfd, ret;
+	DIR *dir;
+
+	*s_dev = 0;
+	dfd = dup(get_service_fd(IMG_FD_OFF));
+	dir = fdopendir(dfd);
+	if (!dir) {
+		close(dfd);
+		pr_perror("Can't open img dir\n");
+		return -1;
+	}
+	rewinddir(dir);
+
+	errno = 0;
+	while ((de = readdir(dir)) != NULL) {
+		if (strncmp(de->d_name, "binfmt-misc-", 12) == 0) {
+			*s_dev = (unsigned int)strtoul(de->d_name + 12, NULL, 10);
+			break;
+		}
+	}
+	ret = errno;
+	if (ret)
+		pr_perror("Can't read dir\n");
+	else if (*s_dev)
+		pr_info("Found binfmt_misc img for dev=%u\n", *s_dev);
+	closedir(dir);
+
+	return ret ? -1 : (*s_dev != 0);
+}
+
 static int binfmt_misc_virtual(struct mount_info *pm)
 {
 	return kerndat_fs_virtualized(KERNDAT_FS_STAT_BINFMT_MISC, pm->s_dev);
@@ -2442,6 +2475,15 @@ static int do_new_mount(struct mount_info *mi)
 	if (tp->restore && tp->restore(mi))
 		return -1;
 
+	if (!mi->mnt_id) {
+		/* C-r time mountpoint, umount it */
+		if (umount(mi->mountpoint) < 0) {
+			pr_perror("Can't umount %s\n", mi->mountpoint);
+			return -1;
+		}
+		goto out;
+	}
+
 	if (remount_ro && mount(NULL, mi->mountpoint, tp->name,
 				     MS_REMOUNT | MS_RDONLY, NULL)) {
 		pr_perror("Unable to apply mount options");
@@ -2461,7 +2503,7 @@ static int do_new_mount(struct mount_info *mi)
 	BUG_ON(mi->master_id);
 	if (restore_shared_options(mi, !mi->shared_id, mi->shared_id, 0))
 		return -1;
-
+out:
 	mi->mounted = true;
 
 	return 0;
@@ -3324,7 +3366,7 @@ static int populate_roots_yard(void)
 
 static int populate_mnt_ns(void)
 {
-	struct mount_info *pms;
+	struct mount_info *pms, *mi;
 	struct ns_id *nsid;
 	struct mount_info *roots_mp = NULL;
 	int ret;
@@ -3343,6 +3385,21 @@ static int populate_mnt_ns(void)
 	if (!pms)
 		return -1;
 
+	for (mi = mntinfo; mi != NULL; mi = mi->next) {
+		if (strcmp(mi->fstype->name, "binfmt_misc") == 0)
+			break;
+	}
+
+	if (!mi) {
+		unsigned int s_dev;
+
+		ret = find_binfmt_misc_img(&s_dev);
+		if (ret > 0)
+			ret = add_cr_time_mount(pms, "binfmt_misc", BINFMT_MISC_HOME, s_dev);
+		if (ret < 0)
+			return -1;
+	}
+
 	if (resolve_shared_mounts(mntinfo, pms->master_id))
 		return -1;