[CRIU] [PATCH v4 2/3] mount: Forced mount unmounted binfmt_misc to do not lost its content
Pavel Emelyanov
xemul at virtuozzo.com
Tue Aug 2 06:00:29 PDT 2016
On 07/20/2016 01:13 PM, Kirill Tkhai wrote:
> Umount does not remove binfmt_misc content. If it's mounted once again,
> the same entries remain registered.
>
> Criu does not dump content of umounted binfmt_misc. So, after C/R we
> lose it at all.
>
> This patch forces mounting of unmounted binfmt_misc after we collected
> mountpoints. If it's unmounted, we mount it back and add this mount
> to the tree of collected mounted mountpoints. Further, binfmt_misc
> content is dumped in usual way with the only difference, that mount
> point itself is not dumped.
>
> v2: Print error in case of umount() fail.
> Move add_forced_mount() to another patch.
> v3: Close binfmt_misc dir before its umount().
> v4: Do not dump forced mounted mountpoint.
>
> Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>
> ---
> criu/cr-dump.c | 1
> criu/include/mount.h | 1
> criu/mount.c | 155 ++++++++++++++++++++++++++++++++++++++++++++++++++
> 3 files changed, 156 insertions(+), 1 deletion(-)
>
> diff --git a/criu/cr-dump.c b/criu/cr-dump.c
> index febef16..b53e45f 100644
> --- a/criu/cr-dump.c
> +++ b/criu/cr-dump.c
> @@ -1616,6 +1616,7 @@ static int cr_dump_finish(int ret)
> if (ret || post_dump_ret || opts.final_state == TASK_ALIVE) {
> network_unlock();
> delete_link_remaps();
> + clean_cr_time_mounts();
> }
> pstree_switch_state(root_item,
> (ret || post_dump_ret) ?
> diff --git a/criu/include/mount.h b/criu/include/mount.h
> index c7992ac..c8668c9 100644
> --- a/criu/include/mount.h
> +++ b/criu/include/mount.h
> @@ -127,5 +127,6 @@ extern int ext_mount_add(char *key, char *val);
> extern int mntns_maybe_create_roots(void);
> extern int read_mnt_ns_img(void);
> extern void cleanup_mnt_ns(void);
> +extern void clean_cr_time_mounts(void);
>
> #endif /* __CR_MOUNT_H__ */
> diff --git a/criu/mount.c b/criu/mount.c
> index 6512f51..d583429 100644
> --- a/criu/mount.c
> +++ b/criu/mount.c
> @@ -40,6 +40,7 @@
> #undef LOG_PREFIX
> #define LOG_PREFIX "mnt: "
>
> +#define BINFMT_MISC_HOME "/proc/sys/fs/binfmt_misc"
> static struct fstype fstypes[];
>
> int ext_mount_add(char *key, char *val)
> @@ -1135,6 +1136,53 @@ static int attach_option(struct mount_info *pm, char *opt)
> return pm->options ? 0 : -1;
> }
>
> +static int add_cr_time_mount(struct mount_info *root, char *fsname, const char *path, unsigned int s_dev)
> +{
> + struct mount_info *mi, *t, *parent;
> +
> + mi = mnt_entry_alloc();
> + if (!mi)
> + return -1;
> + mi->mountpoint = xmalloc(strlen(path) + 2);
> + if (!mi->mountpoint)
> + return -1;
> + mi->ns_mountpoint = mi->mountpoint;
> + sprintf(mi->mountpoint, ".%s", path);
> + mi->mnt_id = mi->flags = mi->sb_flags = 0;
> + mi->root = xstrdup("/");
> + mi->fsname = xstrdup(fsname);
> + mi->source = xstrdup(fsname);
> + mi->options = xstrdup("");
> + if (!mi->root || !mi->fsname || !mi->source || !mi->options)
> + return -1;
> + mi->fstype = find_fstype_by_name(fsname);
> +
> + mi->s_dev = mi->s_dev_rt = s_dev;
> +
> + parent = root;
> + while (1) {
> + list_for_each_entry(t, &parent->children, siblings) {
> + if (strstr(mi->mountpoint, t->mountpoint) == mi->mountpoint) {
The strstr search for substring, you need to check whether one string
_starts_ with another, don't you? We have strstartswith() helper for it.
> + parent = t;
> + break;
> + }
> + }
> + if (&t->siblings == &parent->children)
> + break;
> + }
> +
> + mi->nsid = parent->nsid;
> + mi->parent = parent;
> + mi->parent_mnt_id = parent->mnt_id;
> + mi->next = parent->next;
> + parent->next = mi;
> + list_add(&mi->siblings, &parent->children);
> + pr_info("Add cr-time mountpoint %s with parent %s(%u)\n",
> + mi->mountpoint, parent->mountpoint, parent->mnt_id);
> + return 0;
> +}
> +
> +
> /* Is it mounted w or w/o the newinstance option */
> static int devpts_parse(struct mount_info *pm)
> {
> @@ -1272,6 +1320,65 @@ static int devtmpfs_restore(struct mount_info *pm)
> return ret;
> }
>
> +static int try_mount_binfmt_misc(struct ns_id *ns, unsigned int *s_dev)
> +{
> + int num, mnt_fd, ret, exit_code = -1;
> + struct dirent *de;
> + struct stat st;
> + DIR *dir;
> +
> + ret = switch_ns(ns->ns_pid, &mnt_ns_desc, &mnt_fd);
> + if (ret < 0) {
> + pr_err("Can't switch mnt_ns\n");
> + goto out;
> + }
> +
> + ret = mount("binfmt_misc", BINFMT_MISC_HOME, "binfmt_misc", 0, NULL);
> + if (ret < 0) {
> + if (errno == EPERM) {
> + pr_info("Can't mount binfmt_misc: EPERM. Running in user_ns?\n");
> + exit_code = 0;
> + goto restore_ns;
> + }
> + if (errno != EBUSY && errno != ENODEV && errno != ENOENT) {
> + pr_perror("Can't mount binfmt_misc");
> + goto restore_ns;
> + }
> + pr_info("Prepare binfmt_misc: skipping(%d)\n", errno);
> + } else {
> + dir = opendir(BINFMT_MISC_HOME);
> + if (!dir) {
> + pr_perror("Can't read binfmt_misc dir");
> + goto restore_ns;
> + }
> +
> + num = 0;
> + /* ".", "..", "register", "status" */
> + while (num <= 4 && (de = readdir(dir)) != NULL)
> + num++;
> + closedir(dir);
> + if (num <= 4) {
> + /* No entries */
> + if (umount(BINFMT_MISC_HOME) < 0)
> + pr_perror("Can't umount "BINFMT_MISC_HOME"\n");
> + } else {
> + if (stat(BINFMT_MISC_HOME, &st) < 0)
> + pr_perror("Can't stat on binfmt_misc path\n");
> + else {
> + *s_dev = st.st_dev;
> + exit_code = 1;
> + }
> + goto restore_ns;
> + }
What does this else branch do? Why can't we just add the entry and
let ->dump callback do whatever is appropriate?
> + }
> +
> + exit_code = 0;
> +restore_ns:
> + ret = restore_ns(mnt_fd, &mnt_ns_desc);
> +out:
> + return ret ? -1 : exit_code;
> +}
> +
> static int binfmt_misc_virtual(struct mount_info *pm)
> {
> return kerndat_fs_virtualized(KERNDAT_FS_STAT_BINFMT_MISC, pm->s_dev);
> @@ -1873,6 +1980,11 @@ static int dump_one_mountpoint(struct mount_info *pm, struct cr_img *img)
> if (!pm->dumped && dump_one_fs(pm))
> return -1;
>
> + if (pm->mnt_id == 0) {
> + pr_info("Skip dumping cr-time mountpoint: %s\n", pm->mountpoint);
> + return 0;
> + }
> +
> me.mnt_id = pm->mnt_id;
> me.root_dev = pm->s_dev;
> me.parent_mnt_id = pm->parent_mnt_id;
> @@ -1931,7 +2043,8 @@ static void free_mntinfo(struct mount_info *pms)
>
> struct mount_info *collect_mntinfo(struct ns_id *ns, bool for_dump)
> {
> - struct mount_info *pm;
> + struct mount_info *pm, *mi;
> + int ret;
>
> pm = parse_mountinfo(ns->ns_pid, ns, for_dump);
> if (!pm) {
> @@ -1943,6 +2056,22 @@ struct mount_info *collect_mntinfo(struct ns_id *ns, bool for_dump)
> if (ns->mnt.mntinfo_tree == NULL)
> goto err;
>
> + if (for_dump && ns->type == NS_ROOT) {
> + for (mi = pm; mi != NULL; mi = mi->next) {
> + if (strcmp(mi->fstype->name, "binfmt_misc") == 0)
> + break;
> + }
You don't have to search for the entry, just declare the ->parse callback
and set the boolean flag. Or add flag (or count) on fstype struct and count
for mountpoints of desired fstype.
> + if (!mi) {
> + unsigned int s_dev = 0;
> + ret = try_mount_binfmt_misc(ns, &s_dev);
> + if (ret < 0)
> + return NULL;
> + if (ret > 0 && add_cr_time_mount(ns->mnt.mntinfo_tree, "binfmt_misc",
> + BINFMT_MISC_HOME, s_dev) < 0)
> + return NULL;
> + }
> + }
> +
> ns->mnt.mntinfo_list = pm;
> return pm;
> err:
> @@ -3683,4 +3812,28 @@ int dump_mnt_namespaces(void)
> return 0;
> }
>
> +void clean_cr_time_mounts(void)
> +{
> + struct mount_info *mi;
> + int mnt_fd, ret;
> +
> + for (mi = mntinfo; mi; mi = mi->next) {
> + if (mi->mnt_id)
> + continue;
> + ret = switch_ns(mi->nsid->ns_pid, &mnt_ns_desc, &mnt_fd);
> + if (ret) {
> + pr_err("Can't switch to pid's %u mnt_ns\n", mi->nsid->ns_pid);
> + continue;
> + }
> +
> + if (umount(mi->mountpoint) < 0)
> + pr_perror("Can't umount forced mount %s\n", mi->mountpoint);
> +
> + if (restore_ns(mnt_fd, &mnt_ns_desc)) {
Can we restore it once outside the loop?
> + pr_err("cleanup_forced_mounts exiting with wrong mnt_ns\n");
> + return;
> + }
> + }
> +}
> +
> struct ns_desc mnt_ns_desc = NS_DESC_ENTRY(CLONE_NEWNS, "mnt");
>
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