[CRIU] [PATCH 4/5] [v3] mnt: try to split a mount tree to restore over-mounted mounts
Andrei Vagin
avagin at openvz.org
Wed Dec 7 23:30:09 PST 2016
From: Andrei Vagin <avagin at virtuozzo.com>
If a mount overmounts something else, we can try to restore it
separetly and then move it to the right places after restoring
all mounts.
In this patch if we see that a mount is overmounts something,
we create a new directory in the root yard and restore this
mount and its sub-tree in this directory.
https://bugs.openvz.org/browse/OVZ-6778
v2: add more comments
rename roots_mp into roots_yard_mp
v3: rename functions
Signed-off-by: Andrei Vagin <avagin at virtuozzo.com>
---
criu/mount.c | 159 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 158 insertions(+), 1 deletion(-)
diff --git a/criu/mount.c b/criu/mount.c
index a578b0e..0421f67 100644
--- a/criu/mount.c
+++ b/criu/mount.c
@@ -736,7 +736,8 @@ static int validate_mounts(struct mount_info *info, bool for_dump)
}
}
skip_fstype:
- if (does_mnt_overmount(m)) {
+ if (does_mnt_overmount(m) &&
+ !list_empty(&m->parent->mnt_share)) {
pr_err("Unable to handle mounts under %d:%s\n",
m->mnt_id, m->mountpoint);
return -1;
@@ -2162,6 +2163,144 @@ static int do_umount_one(struct mount_info *mi)
return 0;
}
+/*
+ * If a mount overmounts other mounts, it is restored separetly in the roots
+ * yard and then moved to the right place.
+ *
+ * mnt_remap_entry is created for each such mount and it's added into
+ * mnt_remap_list. The origin mount point is replaced on a new one in
+ * roots_yard where it will be restored. The remapped mount will be
+ * moved to the right places after restoring all mounts.
+ */
+
+static inline int print_ns_root(struct ns_id *ns, int remap_id, char *buf, int bs);
+static int get_mp_mountpoint(char *mountpoint, struct mount_info *mi, char *root, int root_len);
+
+static LIST_HEAD(mnt_remap_list);
+static int remap_id;
+
+struct mnt_remap_entry {
+ struct mount_info *mi; /* child is remaped into the root yards */
+ struct mount_info *parent; /* the origin parent for the child*/
+ struct list_head node;
+};
+
+static int do_mnt_remap(struct mount_info *m)
+{
+ int len;
+
+ if (m->nsid->type == NS_OTHER) {
+ /*
+ * m->mountpoint already contains a roots_yard prefix and
+ * it has a fixed size, so it can be just replaced.
+ */
+ len = print_ns_root(m->nsid, remap_id, m->mountpoint, PATH_MAX);
+ m->mountpoint[len] = '/';
+ } else if (m->nsid->type == NS_ROOT) {
+ char root[PATH_MAX], *mp, *ns_mp;
+ int len, ret;
+
+ /*
+ * Allocate a new path in the roots yard. m->mountpoint in the
+ * root namespace doesn't have a roots_yard prefix, so its
+ * size has to be changed and a new storage has to be
+ * allocated.
+ */
+ mp = m->mountpoint; ns_mp = m->ns_mountpoint;
+
+ len = print_ns_root(m->nsid, remap_id, root, PATH_MAX);
+
+ ret = get_mp_mountpoint(ns_mp, m, root, len);
+ if (ret < 0)
+ return ret;
+ xfree(mp);
+ } else
+ BUG();
+ return 0;
+}
+
+static int try_remap_mount(struct mount_info *m)
+{
+ struct mnt_remap_entry *r;
+
+ if (!does_mnt_overmount(m))
+ return 0;
+
+ BUG_ON(!m->parent || !list_empty(&m->parent->mnt_share));
+
+ r = xmalloc(sizeof(struct mnt_remap_entry));
+ if (!r)
+ return -1;
+
+ r->mi = m;
+ list_add(&r->node, &mnt_remap_list);
+
+ return 0;
+}
+
+static int find_remap_mounts(struct mount_info *root)
+{
+ struct mnt_remap_entry *r;
+ struct mount_info *m;
+
+ /*
+ * It's impossible to change a tree without interrupting
+ * enumeration, so on the first step mounts are added
+ * into mnt_remap_list and then they are connected to root_yard_mp.
+ */
+ if (mnt_tree_for_each(root, try_remap_mount))
+ return -1;
+
+ /* Move remapped mounts to root_yard */
+ list_for_each_entry(r, &mnt_remap_list, node) {
+ m = r->mi;
+ r->parent = m->parent;
+ m->parent = root_yard_mp;
+ list_del(&m->siblings);
+ list_add(&m->siblings, &root_yard_mp->children);
+
+ remap_id++;
+ mnt_tree_for_each(m, do_mnt_remap);
+ pr_debug("Restore the %d mount in %s\n", m->mnt_id, m->mountpoint);
+ }
+
+ return 0;
+}
+
+/* Move remapped mounts to places where they have to be */
+static int fini_remap_mounts()
+{
+ struct mnt_remap_entry *r;
+
+ list_for_each_entry(r, &mnt_remap_list, node) {
+ struct mount_info *m = r->mi;
+ char path[PATH_MAX];
+ int len;
+
+ if (m->nsid->type == NS_ROOT) {
+ path[0] = '.';
+ strncpy(path + 1, m->ns_mountpoint, PATH_MAX - 1);
+ } else {
+ strncpy(path, m->mountpoint, PATH_MAX);
+ len = print_ns_root(m->nsid, 0, path, PATH_MAX);
+ path[len] = '/';
+ }
+
+ pr_debug("Move mount %s -> %s\n", m->mountpoint, path);
+ if (mount(m->mountpoint, path, NULL, MS_MOVE, NULL)) {
+ pr_perror("Unable to move mount %s -> %s", m->mountpoint, path);
+ return -1;
+ }
+
+ /* Insert child back to its place in the tree */
+ list_del(&r->mi->siblings);
+ list_add(&r->mi->siblings, &r->parent->children);
+ r->mi->parent = r->parent;
+ }
+
+ return 0;
+}
+
static int cr_pivot_root(char *root)
{
char tmp_dir_tmpl[] = "crtools-put-root.XXXXXX";
@@ -2637,6 +2776,7 @@ void fini_restore_mntns(void)
*/
static int populate_roots_yard(void)
{
+ struct mnt_remap_entry *r;
char path[PATH_MAX];
struct ns_id *nsid;
@@ -2657,6 +2797,17 @@ static int populate_roots_yard(void)
}
}
+ /*
+ * mnt_remap_list is filled in find_remap_mounts() and
+ * contains mounts which has to be restored separatly
+ */
+ list_for_each_entry(r, &mnt_remap_list, node) {
+ if (mkdirpat(AT_FDCWD, r->mi->mountpoint, 0755)) {
+ pr_perror("Unable to create %s", r->mi->mountpoint);
+ return -1;
+ }
+ }
+
return 0;
}
@@ -2707,6 +2858,9 @@ static int populate_mnt_ns(void)
if (validate_mounts(mntinfo, false))
return -1;
+ if (find_remap_mounts(pms))
+ return -1;
+
/*
* Set properties for the root before mounting a root yard,
* otherwise the root yard can be propagated into the host
@@ -2724,6 +2878,9 @@ static int populate_mnt_ns(void)
ret = mnt_tree_for_each(pms, do_mount_one);
mnt_tree_for_each(pms, do_close_one);
+ if (ret == 0 && fini_remap_mounts())
+ return -1;
+
if (umount_clean_path())
return -1;
return ret;
--
2.7.4
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