Hi Miklos,
Wanted to give you a heads up on upcoming announcement for
overlayfs snapshots POC, just to give you a sense of what's been
driving my recent overlayfs development efforts
and also because I am eager to share the news ;-).
I still need to sort out some documentation with FAQ and use cases
before I make a more public announcement of the project. I intend
to get to it next week and post a talk proposal to LSF/MM.
An example to make a long story short:
mount -t overlay -o lowerdir=/lower,upperdir=/upper,workdir=/work
none /snaphot
mount -t snapshot -o upperdir=/lower,snapshot=/snapshot
none /mnt
/mnt is a rw view of /lower, where every mutation is preceded
by "copy-down" to upper.
/snapshot is an overlay view of lower+upper where content
remains stable.
I instrumented unionmount-testsuite with run --sn for running tests on the
setup described in the example above (in my githib #ovl_snapshot branch).
I am pleased to say that all test now pass successfully, including content
validation of files in /snapshot after every test (before and after remount).
The patches to overlayfs are not so intrusive IMO and can be found on
my github #ovl_snapshot branch.
As a matter of fact, most of the changes can be maintained as a forked
module for the development period. The module registers itself as fs type
snapshot and used for the second stacked mount.
At the moment there are only 2 modifications required from the underlying
"vanilla" overlayfs mount:
1. #redirect_fh, which #ovl_snapshot is based on
redirect_fh allows moving directories in lower without breaking the
downwards reference from upper
2. "explicit whiteout" - place preemptive whiteout in upper
(see patch #2), which does not affect normal overlayfs ops
and does not break any assumptions as far as I can tell
Thanks for all your help and patience so far!
Amir.
Amir Goldstein (9):
ovl: introduce snapshot mount
ovl: explicit copy up/whiteout requests from snapshot mount
ovl: implement snapshot mount lookup
ovl: cow file to snapshot on open for write
ovl: cow file/dir to snapshot on ovl_want_write()
ovl: redirect dir on rename in snapshot mount
ovl: fix set_acl crash with snapshot mount
ovl: unhash removed dentries from snapshot
ovl: real dir operations for snapshot mount
fs/overlayfs/Kconfig | 8 ++
fs/overlayfs/Makefile | 1 +
fs/overlayfs/dir.c | 52 ++++++++--
fs/overlayfs/inode.c | 2 +-
fs/overlayfs/namei.c | 27 ++++-
fs/overlayfs/overlayfs.h | 14 +++
fs/overlayfs/ovl_entry.h | 7 +-
fs/overlayfs/readdir.c | 4 +-
fs/overlayfs/snapshot.c | 115 +++++++++++++++++++++
fs/overlayfs/super.c | 256 +++++++++++++++++++++++++++++++++++++++++------
fs/overlayfs/util.c | 17 ++++
11 files changed, 458 insertions(+), 45 deletions(-)
create mode 100644 fs/overlayfs/snapshot.c
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