On Thu, May 25, 2023 at 6:21 PM Alexander Larsson <alexl@xxxxxxxxxx> wrote: > > Something that came up about this in a discussion recently was > multi-layer composefs style images. For example, this may be a useful > approach for multi-layer container images. > > In such a setup you would have one lowerdata layer, but two real > lowerdirs, like lowerdir=A:B::C. In this situation a file in B may > accidentally have the same name as a file on C, causing a redirect > from A to end up in B instead of C. > I was under the impression that the names of the data blobs in C are supposed to be content derived names (hash). Is this not the case or is the concern about hash conflicts? > Would it be possible to have a syntax for redirects that mean "only > lookup in lowerdata layers. For example a double-slash path > //some/file. > Anything is possible if we can define the problem that needs to be solved. In this case, I did not understand why the problem is limited to finding a file by mistake in layer B. If there are several data layers A:B::C:D why wouldn't we have the same problem with a file name collision between C and D? So if there was a need to be able to redirect to a specific layer, I would imagine that we would need to be able to address any layer and not just "the start of data layers". If we were looking for a syntax that is not a current valid redirect, anything with // would work as well as anything with / that is not an absolute path, e.g. 3:/path/to/file, so both NFS and SMB ;-) Please describe the problem with more details and examples. Thanks, Amir. > On Thu, Apr 27, 2023 at 3:06 PM Amir Goldstein <amir73il@xxxxxxxxx> wrote: > > > > Miklos, > > > > This v2 combines the prep patch set [1] and lazy lookup patch set [2]. > > > > This work is motivated by Alexander's composefs use case. > > Alexander has been developing and testing his fsverity patches over > > my lazy-lowerdata-lookup branch [3]. > > > > Alexander has also written tests for lazy lowerdata lookup [4]. > > > > Note that patch #1 is a Fixes patch for stable. > > Gao commented that the fix may not be complete, but I think it is better > > than no fix at all. > > > > Regarding lazy lookup in d_real(), I am not sure if the best effort > > lookup is the best solution, but in any case, none of this code kicks in > > without explicit opt-in to data-only layers, so the risk of breaking > > existing setups is quite low. > > > > Thanks, > > Amir. > > > > Changes since v1: > > - Include the prep patch set > > - Split remove lowerdata from add lowerdata_redirect patch > > - Remove embedded ovl_entry stack optimization > > - Add lazy lookup and comment in d_real_inode() > > - Improve documentation of :: data-only layers syntax > > - Added RVBs > > > > [1] https://lore.kernel.org/linux-unionfs/20230408164302.1392694-1-amir73il@xxxxxxxxx/ > > [2] https://lore.kernel.org/linux-unionfs/20230412135412.1684197-1-amir73il@xxxxxxxxx/ > > [3] https://github.com/amir73il/linux/commits/ovl-lazy-lowerdata > > [4] https://github.com/amir73il/xfstests/commits/ovl-lazy-lowerdata > > > > Amir Goldstein (13): > > ovl: update of dentry revalidate flags after copy up > > ovl: use OVL_E() and OVL_E_FLAGS() accessors > > ovl: use ovl_numlower() and ovl_lowerstack() accessors > > ovl: factor out ovl_free_entry() and ovl_stack_*() helpers > > ovl: move ovl_entry into ovl_inode > > ovl: deduplicate lowerpath and lowerstack[] > > ovl: deduplicate lowerdata and lowerstack[] > > ovl: remove unneeded goto instructions > > ovl: introduce data-only lower layers > > ovl: implement lookup in data-only layers > > ovl: prepare to store lowerdata redirect for lazy lowerdata lookup > > ovl: prepare for lazy lookup of lowerdata inode > > ovl: implement lazy lookup of lowerdata in data-only layers > > > > Documentation/filesystems/overlayfs.rst | 36 +++++ > > fs/overlayfs/copy_up.c | 11 ++ > > fs/overlayfs/dir.c | 3 +- > > fs/overlayfs/export.c | 41 +++--- > > fs/overlayfs/file.c | 21 ++- > > fs/overlayfs/inode.c | 38 +++-- > > fs/overlayfs/namei.c | 185 +++++++++++++++++++----- > > fs/overlayfs/overlayfs.h | 20 ++- > > fs/overlayfs/ovl_entry.h | 73 ++++++++-- > > fs/overlayfs/super.c | 132 ++++++++++------- > > fs/overlayfs/util.c | 165 ++++++++++++++++----- > > 11 files changed, 534 insertions(+), 191 deletions(-) > > > > -- > > 2.34.1 > > > > > -- > =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= > Alexander Larsson Red Hat, Inc > alexl@xxxxxxxxxx alexander.larsson@xxxxxxxxx >
