Hi Amir, thanks for your suggestions.
On 2018/3/23 20:32, Amir Goldstein Wrote:
On Thu, Mar 22, 2018 at 1:35 PM, zhangyi (F) <yi.zhang@xxxxxxxxxx> wrote:
Hi All,
This is overlay feature set support patches, introduce incompatable,
read-only compatable and incompatable feature set, store on the upper
root dir via "trusted.overlay.feature_[compat|ro_compat|incompat]"
xattrs.
Hi Zhangyi!
Thanks again for working on this.
For the "features" feature to be complete I think one more thing is required.
I suggest to refer to the era before "features" as overlayfs on-disk format v1
and to the era after "features" + fsck.overlayfs as on-disk format v2.
On-disk format v2 is identified by the existence of the features xattrs, even
if the are empty.
Every layer in the overlay can be of either format v1 or v2, but when you run
fsck.overlay it will scan all layers for undeclared features and
"upgrade" the layers
to v2, by explicitly stating the empty or non-empty feature sets of the layer.
> So the thing that is missing IMO is -
a Kconfig option (say OVERLAY_FS_V2 ot OVERLAY_FS_FEATURES)
which defaults to n, but allows distros to opt-in for "v2 only".
With that config option set, overlay will refuse to mount v1 layers, or in other
words, fsck.overlay must be run before first time mount, or a simple
mkfs.overlay
to initialize the features xattrs
Let me see, if "OVERLAY_FS_V2=y",
- overlay will refuse to mount overlayfs which was mounted on old
kernel, user should run fsck.overlay to check features in each layer
and set feature xattr on the layer's root dir. So the feature xattr on
one root dir only contain this layer's features.
- overlay will refuse to mount overlayfs whose upper is empty(no feature
xattr), maybe new created image and never mounted before,
uesr should run a simple mkfs.overlay to init the feature xattr for all
layers (maybe accept -o options to enable features).
and if "OVERLAY_FS_V2=n",
This is what we do now in kernel, features xattr will set in the upper
root dir according to mount options (or maybe where we set xattrs used
by features, like redirect). And one more thing should do is init an
empty feature xattr if user don't give any feature mount options.
Right?
Another option is to relax the requirement for declaring lower layers features
and leave only the requirement that upper root dir is either empty or has the
features xattrs. In any case, on first mount with an empty upper dir,
features xattrs
should be initialized. Maybe that calls for yet another Kconfig option, i.e.
OVERLAY_FS_LOWER_V2.
Sorry, I don't follow this option.
Do you mean this option is a sub-option of OVERLAY_FS_V2 ?
If "OVERLAY_FS_LOWER_V2=y", refuse to mount just if there is no feature
xattrs on the upper root dir (empty or non-empty will pass). Introduce
this option because overlayfs only set feature xattrs on the upper
layer, so there is no feature xattrs on the lower root dir, right or
some other reasons ?
Now, the quesion is:
The feature xattrs on the upper root dir should contain all features in
the overlayfs(1), or features just in the upper layer(2), not sure which
one is better ?
If (1), say "this overlayfs image have index feature, not this layer",
it's easy to do but we will meet the indexdir problem you mentioned in 2/4.
if (2), the auto fix (e.g. fix redirect feature if we detect redirect
xattr) becomes useless becase we cannot set feature xattr to the lower
root dir, so need to remove this implement or give a warn to ask
fsck.overlay to handle this. But we can distinguish features in the
upper layer and lowers layer, maybe useful in the future.
Thanks,
Yi
This patch set base on Linux 4.16-rc6.
Patch 1: Implement feature xattr and mount check, refuse mount if no
backward incompatible feature is detected.
Patch 2: Copy up feature xattr from the lower root dirs to the upper
root dir to prevent feature lost.
Patch 3: Add three already support feature: redirect dir, index and
nfs_export, enable them when user give enable mount option.
patch 4: Fix redircet feature once a redirect xattr is detected for
the case of overlay was mounted in the old kernel.
(PS: Not sure this patch is necessary, maybe just give a warning message
and handle this by fsck.overlay? If necessary, check indexdir during
mount time is also necessary too).
zhangyi (F) (4):
ovl: add feature set support
ovl: update features on upper root dir from lower layers
ovl: enable features according to mount options
ovl: fix redirect feature for backward compatibility
fs/overlayfs/namei.c | 12 ++
fs/overlayfs/overlayfs.h | 90 +++++++++++
fs/overlayfs/ovl_entry.h | 18 +++
fs/overlayfs/super.c | 410 ++++++++++++++++++++++++++++++++++++++++++++++-
4 files changed, 525 insertions(+), 5 deletions(-)
--
2.13.6
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