On Tue, Sep 12, 2023 at 12:56 PM Alexander Larsson <alexl@xxxxxxxxxx> wrote: > > 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 tmpfs), then you cannot currently store > a lowerdir on the rootfs, because the inner overlayfs will eat all the whiteouts > and overlay xattrs. This means you can't e.g. store on the rootfs a prepared > container image for use with overlayfs. > > This patch series adds support for nesting of overlayfs mounts by escaping the > problematic features and unescaping them when exposing to the overlayfs user. > > This series is also available here: > https://github.com/alexlarsson/linux/tree/ovl-nesting > > And xfstest to test it is available here: > https://github.com/alexlarsson/xfstests/tree/overlayfs-nesting > > The overlay/083 test checks both xattr escaping, the new whiteouts as well as > actual nesting of overlayfs. > > Note that this series breaks the overlay/026 test which validates that > writing overlay.* xattrs is not supported, but it now is. I'm not sure > if we should fix this test to not fail, or if we should make this an > opt-in mount feature. Please fix the test as we discussed: 1. relax the requirement that getxattr trusted.overlay should fail 2. set expectations for setxattr depending on result of getxattr This way we will not lose much test coverage for old kernels. This test fix can be posted to fstests ahead of time as preparation for your patch set. Given that this version has dropped the controversial bits and that the whiteout implementation is the one that was proposed by Miklos, I don't see any problem with it now. I can queue it up for 6.7 and if Miklos has any objections or comments, we have enough time to address them. Thanks, Amir. > > Changes since v3: > * Dropped the handling of whiteout xattrs across layers. > * Copy-up escaped overlayfs xattrs. > * Minor code cleanups. > > Changes since v2: > * Uses a new approach for escaping whiteouts with a regular file with an > overlay.whiteout xattr in a lower directory with an overlay.whiteouts > xattr. > > Changes since v1: > > * Moved all xattr handling to xattr.c > * Made creation of escaped whiteouts atomic > > Alexander Larsson (5): > ovl: Move xattr support to new xattrs.c file > ovl: Add OVL_XATTR_TRUSTED/USER_PREFIX_LEN macros > ovl: Support escaped overlay.* xattrs > ovl: Add an alternative type of whiteout > ovl: Add documentation on nesting of overlayfs mounts > > Documentation/filesystems/overlayfs.rst | 23 ++ > fs/overlayfs/Makefile | 2 +- > fs/overlayfs/dir.c | 4 +- > fs/overlayfs/inode.c | 124 ----------- > fs/overlayfs/namei.c | 15 +- > fs/overlayfs/overlayfs.h | 42 +++- > fs/overlayfs/readdir.c | 27 ++- > fs/overlayfs/super.c | 67 +----- > fs/overlayfs/util.c | 40 ++++ > fs/overlayfs/xattrs.c | 273 ++++++++++++++++++++++++ > 10 files changed, 404 insertions(+), 213 deletions(-) > create mode 100644 fs/overlayfs/xattrs.c > > -- > 2.41.0 >
