With index=on, overlayfs instances are non-migratable, meaning that
the layers cannot be copied without breaking the index.
So when indexdir exists, store a persistent uuid in xattr on the
indexdir to give the overlayfs instance a persistent identifier.
This also makes f_fsid persistent and more reliable for reporting
fid info in fanotify events.
With mount option uuid=nogen, a persistent uuid is not be initialized
on indexdir, but if a persistent uuid already exists, it will be used.
Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>
---
fs/overlayfs/overlayfs.h | 3 +++
fs/overlayfs/super.c | 7 +++++++
fs/overlayfs/util.c | 41 ++++++++++++++++++++++++++++++++++++++++
3 files changed, 51 insertions(+)
diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
index dcdb02d0ddf8..9927472a3aaa 100644
--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h
@@ -36,6 +36,7 @@ enum ovl_xattr {
OVL_XATTR_IMPURE,
OVL_XATTR_NLINK,
OVL_XATTR_UPPER,
+ OVL_XATTR_UUID,
OVL_XATTR_METACOPY,
OVL_XATTR_PROTATTR,
};
@@ -431,6 +432,8 @@ bool ovl_already_copied_up(struct dentry *dentry, int flags);
bool ovl_path_check_dir_xattr(struct ovl_fs *ofs, const struct path *path,
enum ovl_xattr ox);
bool ovl_path_check_origin_xattr(struct ovl_fs *ofs, const struct path *path);
+bool ovl_init_uuid_xattr(struct super_block *sb, struct ovl_fs *ofs,
+ struct dentry *upperdentry, bool set);
static inline bool ovl_check_origin_xattr(struct ovl_fs *ofs,
struct dentry *upperdentry)
diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index ad2250f98b38..8364620e8722 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -1535,6 +1535,9 @@ static int ovl_get_indexdir(struct super_block *sb, struct ovl_fs *ofs,
if (err)
pr_err("failed to verify index dir 'upper' xattr\n");
+ /* Best effort get or set persistent uuid */
+ ovl_init_uuid_xattr(sb, ofs, ofs->indexdir, true);
+
/* Cleanup bad/stale/orphan index entries */
if (!err)
err = ovl_indexdir_cleanup(ofs);
@@ -2052,6 +2055,10 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
ovl_uuid_str[ofs->config.uuid]);
}
+ /*
+ * This uuid may be overridden by a persistent uuid stored in xattr on
+ * index dir and it may be persisted in xattr on first index=on mount.
+ */
if (ovl_want_uuid_gen(ofs))
uuid_gen(&sb->s_uuid);
diff --git a/fs/overlayfs/util.c b/fs/overlayfs/util.c
index 923d66d131c1..8902db4b2975 100644
--- a/fs/overlayfs/util.c
+++ b/fs/overlayfs/util.c
@@ -589,6 +589,45 @@ bool ovl_path_check_origin_xattr(struct ovl_fs *ofs, const struct path *path)
return false;
}
+/*
+ * Load persistent uuid from xattr into s_uuid if found, possibly overriding
+ * the random generated value in s_uuid.
+ * Otherwise, if @set is true and s_uuid contains a valid value, store this
+ * value in xattr.
+ */
+bool ovl_init_uuid_xattr(struct super_block *sb, struct ovl_fs *ofs,
+ struct dentry *upperdentry, bool set)
+{
+ struct path path = {
+ .dentry = upperdentry,
+ .mnt = ovl_upper_mnt(ofs),
+ };
+ uuid_t uuid;
+ int res;
+
+ res = ovl_path_getxattr(ofs, &path, OVL_XATTR_UUID, uuid.b, UUID_SIZE);
+ if (res == UUID_SIZE) {
+ uuid_copy(&sb->s_uuid, &uuid);
+ return true;
+ }
+
+ if (res == -ENODATA) {
+ if (!set || uuid_is_null(&sb->s_uuid))
+ return false;
+
+ res = ovl_setxattr(ofs, upperdentry, OVL_XATTR_UUID,
+ sb->s_uuid.b, UUID_SIZE);
+ if (res == 0)
+ return true;
+ } else {
+ set = false;
+ }
+
+ pr_warn("failed to %s uuid (%pd2, err=%i)\n",
+ set ? "set" : "get", upperdentry, res);
+ return false;
+}
+
bool ovl_path_check_dir_xattr(struct ovl_fs *ofs, const struct path *path,
enum ovl_xattr ox)
{
@@ -611,6 +650,7 @@ bool ovl_path_check_dir_xattr(struct ovl_fs *ofs, const struct path *path,
#define OVL_XATTR_IMPURE_POSTFIX "impure"
#define OVL_XATTR_NLINK_POSTFIX "nlink"
#define OVL_XATTR_UPPER_POSTFIX "upper"
+#define OVL_XATTR_UUID_POSTFIX "uuid"
#define OVL_XATTR_METACOPY_POSTFIX "metacopy"
#define OVL_XATTR_PROTATTR_POSTFIX "protattr"
@@ -625,6 +665,7 @@ const char *const ovl_xattr_table[][2] = {
OVL_XATTR_TAB_ENTRY(OVL_XATTR_IMPURE),
OVL_XATTR_TAB_ENTRY(OVL_XATTR_NLINK),
OVL_XATTR_TAB_ENTRY(OVL_XATTR_UPPER),
+ OVL_XATTR_TAB_ENTRY(OVL_XATTR_UUID),
OVL_XATTR_TAB_ENTRY(OVL_XATTR_METACOPY),
OVL_XATTR_TAB_ENTRY(OVL_XATTR_PROTATTR),
};
--
2.34.1
