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| author | Alexander Larsson <alexl@redhat.com> | 2023-08-15 09:40:50 +0200 |
|---|---|---|
| committer | Amir Goldstein <amir73il@gmail.com> | 2023-10-31 00:12:59 +0200 |
| commit | dad02fad84cbce30f317b69a4f2391f90045f79d (patch) | |
| tree | 87e40882bd788ccb619dc683ea21c97605643c2c /fs/overlayfs/overlayfs.h | |
| parent | d431e652600bf2708f5a5ca3b46fa1b53606d1cf (diff) | |
ovl: Support escaped overlay.* xattrs
There are cases where you want to use an overlayfs mount as a lowerdir
for another overlayfs mount. For example, if the system rootfs is on
overlayfs due to composefs, or to make it volatile (via tmps), then
you cannot currently store a lowerdir on the rootfs. This means you
can't e.g. store on the rootfs a prepared container image for use
using overlayfs.
To work around this, we introduce an escapment mechanism for overlayfs
xattrs. Whenever the lower/upper dir has a xattr named
"overlay.overlay.XYZ", we list it as "overlay.XYZ" in listxattrs, and
when the user calls getxattr or setxattr on "overlay.XYZ", we apply to
"overlay.overlay.XYZ" in the backing directories.
This allows storing any kind of overlay xattrs in a overlayfs mount
that can be used as a lowerdir in another mount. It is possible to
stack this mechanism multiple times, such that
"overlay.overlay.overlay.XYZ" will survive two levels of overlay mounts,
however this is not all that useful in practice because of stack depth
limitations of overlayfs mounts.
Note: These escaped xattrs are copied to upper during copy-up.
Signed-off-by: Alexander Larsson <alexl@redhat.com>
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Diffstat (limited to 'fs/overlayfs/overlayfs.h')
| -rw-r--r-- | fs/overlayfs/overlayfs.h | 7 |
1 files changed, 7 insertions, 0 deletions
diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h index 1c0ad84646e8..393c6ba9bffa 100644 --- a/fs/overlayfs/overlayfs.h +++ b/fs/overlayfs/overlayfs.h @@ -32,6 +32,13 @@ enum ovl_path_type { #define OVL_XATTR_USER_PREFIX XATTR_USER_PREFIX OVL_XATTR_NAMESPACE #define OVL_XATTR_USER_PREFIX_LEN (sizeof(OVL_XATTR_USER_PREFIX) - 1) +#define OVL_XATTR_ESCAPE_PREFIX OVL_XATTR_NAMESPACE +#define OVL_XATTR_ESCAPE_PREFIX_LEN (sizeof(OVL_XATTR_ESCAPE_PREFIX) - 1) +#define OVL_XATTR_ESCAPE_TRUSTED_PREFIX OVL_XATTR_TRUSTED_PREFIX OVL_XATTR_ESCAPE_PREFIX +#define OVL_XATTR_ESCAPE_TRUSTED_PREFIX_LEN (sizeof(OVL_XATTR_ESCAPE_TRUSTED_PREFIX) - 1) +#define OVL_XATTR_ESCAPE_USER_PREFIX OVL_XATTR_USER_PREFIX OVL_XATTR_ESCAPE_PREFIX +#define OVL_XATTR_ESCAPE_USER_PREFIX_LEN (sizeof(OVL_XATTR_ESCAPE_USER_PREFIX) - 1) + enum ovl_xattr { OVL_XATTR_OPAQUE, OVL_XATTR_REDIRECT, |