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authorAmir Goldstein <amir73il@gmail.com>2023-07-07 10:26:29 +0200
committerAmir Goldstein <amir73il@gmail.com>2023-08-12 18:02:50 +0200
commitcbb44f0935974bba997f8db0458fac5739ae0009 (patch)
treec32f08f3a699457bbcf17a0e6b6e180d50732233
parentovl: store persistent uuid/fsid with uuid=on (diff)
downloadlinux-cbb44f0935974bba997f8db0458fac5739ae0009.tar.xz
linux-cbb44f0935974bba997f8db0458fac5739ae0009.zip
ovl: auto generate uuid for new overlay filesystems
Add a new mount option uuid=auto, which is the default. If a persistent UUID xattr is found it is used. Otherwise, an existing ovelrayfs with copied up subdirs in upper dir that was never mounted with uuid=on retains the null UUID. A new overlayfs with no copied up subdirs, generates the persistent UUID on first mount. Signed-off-by: Amir Goldstein <amir73il@gmail.com>
-rw-r--r--Documentation/filesystems/overlayfs.rst8
-rw-r--r--fs/overlayfs/overlayfs.h4
-rw-r--r--fs/overlayfs/params.c3
-rw-r--r--fs/overlayfs/util.c22
4 files changed, 34 insertions, 3 deletions
diff --git a/Documentation/filesystems/overlayfs.rst b/Documentation/filesystems/overlayfs.rst
index 8275ed735f77..35853906accb 100644
--- a/Documentation/filesystems/overlayfs.rst
+++ b/Documentation/filesystems/overlayfs.rst
@@ -664,7 +664,7 @@ UUID and fsid
The UUID of overlayfs instance itself and the fsid reported by statfs(2) are
controlled by the "uuid" mount option, which supports these values:
-- "null": (default)
+- "null":
UUID of overlayfs is null. fsid is taken from upper most filesystem.
- "off":
UUID of overlayfs is null. fsid is taken from upper most filesystem.
@@ -674,6 +674,12 @@ controlled by the "uuid" mount option, which supports these values:
UUID is stored in xattr "trusted.overlay.uuid", making overlayfs fsid
unique and persistent. This option requires an overlayfs with upper
filesystem that supports xattrs.
+- "auto": (default)
+ UUID is taken from xattr "trusted.overlay.uuid" if it exists.
+ Upgrade to "uuid=on" on first time mount of new overlay filesystem that
+ meets the prerequites.
+ Downgrade to "uuid=null" for existing overlay filesystems that were never
+ mounted with "uuid=on".
Volatile mount
diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
index 8b026d758eaf..72f57d919aa9 100644
--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h
@@ -71,6 +71,7 @@ enum {
enum {
OVL_UUID_OFF,
OVL_UUID_NULL,
+ OVL_UUID_AUTO,
OVL_UUID_ON,
};
@@ -550,7 +551,8 @@ static inline bool ovl_origin_uuid(struct ovl_fs *ofs)
static inline bool ovl_has_fsid(struct ovl_fs *ofs)
{
- return ofs->config.uuid == OVL_UUID_ON;
+ return ofs->config.uuid == OVL_UUID_ON ||
+ ofs->config.uuid == OVL_UUID_AUTO;
}
/*
diff --git a/fs/overlayfs/params.c b/fs/overlayfs/params.c
index 5a59c87c1dfe..3fc01feb5f12 100644
--- a/fs/overlayfs/params.c
+++ b/fs/overlayfs/params.c
@@ -68,6 +68,7 @@ static const struct constant_table ovl_parameter_bool[] = {
static const struct constant_table ovl_parameter_uuid[] = {
{ "off", OVL_UUID_OFF },
{ "null", OVL_UUID_NULL },
+ { "auto", OVL_UUID_AUTO },
{ "on", OVL_UUID_ON },
{}
};
@@ -79,7 +80,7 @@ static const char *ovl_uuid_mode(struct ovl_config *config)
static int ovl_uuid_def(void)
{
- return OVL_UUID_NULL;
+ return OVL_UUID_AUTO;
}
static const struct constant_table ovl_parameter_xino[] = {
diff --git a/fs/overlayfs/util.c b/fs/overlayfs/util.c
index 8602982ae579..9ebb9598e7ec 100644
--- a/fs/overlayfs/util.c
+++ b/fs/overlayfs/util.c
@@ -695,6 +695,28 @@ bool ovl_init_uuid_xattr(struct super_block *sb, struct ovl_fs *ofs,
if (res != -ENODATA)
goto fail;
+ /*
+ * With uuid=auto, if uuid xattr is found, it will be used.
+ * If uuid xattrs is not found, generate a persistent uuid only on mount
+ * of new overlays where upper root dir is not yet marked as impure.
+ * An upper dir is marked as impure on copy up or lookup of its subdirs.
+ */
+ if (ofs->config.uuid == OVL_UUID_AUTO) {
+ res = ovl_path_getxattr(ofs, upperpath, OVL_XATTR_IMPURE, NULL,
+ 0);
+ if (res > 0) {
+ /* Any mount of old overlay - downgrade to uuid=null */
+ ofs->config.uuid = OVL_UUID_NULL;
+ return true;
+ } else if (res == -ENODATA) {
+ /* First mount of new overlay - upgrade to uuid=on */
+ ofs->config.uuid = OVL_UUID_ON;
+ } else if (res < 0) {
+ goto fail;
+ }
+
+ }
+
/* Generate overlay instance uuid */
uuid_gen(&sb->s_uuid);