Commit cbb44f09 authored by Amir Goldstein's avatar Amir Goldstein
Browse files

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: default avatarAmir Goldstein <amir73il@gmail.com>
parent d9544c1b

Documentation/filesystems/overlayfs.rst

+7 −1
Original line number Diff line number Diff line
@@ -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

fs/overlayfs/overlayfs.h

+3 −1
Original line number Diff line number Diff line
@@ -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;

}



/*

fs/overlayfs/params.c

+2 −1
Original line number Diff line number Diff line
@@ -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[] = {

fs/overlayfs/util.c

+22 −0
Original line number Diff line number Diff line
@@ -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);