On Fri, Dec 15, 2017 at 5:35 AM, zhangyi (F) <yi.zhang@xxxxxxxxxx> wrote:
> On 2017/12/14 22:13, Miklos Szeredi Wrote:
[...]
>>
>>>
>>> Opaque directories
>>> ------------------
>>>
>>> An opaque directory is a directory with "trusted.overlay.opaque" xattr
>>> valued "y". There are two legal situations of making opaque directory: 1)
>>> create directory over whiteout 2) creat directory in merged directory. If an
>>> opaque directory is found, corresponding matching name in lower layers might
>>> exist or parent directory might merged, If not, the opaque xattr will be
>>> treated as invalid and remove.
>>
>> Current version of overlay fs doesn't bother with removing opaque
>> attribute. So not sure fsck.overlay should care. Or at least is
>> should be an optional thing and not worth warning about, since it's
>> perfectly normal.
>>
> Indeed, we can introduce '-f' option to handle this (e2fsck(8)):
>
> -f Force checking even if the file system seems clean.
>
Hmm, I would not use -f for that, because it means something completely
different in e2fsck.
ext4 has a "clean" super block flag, which is set on clean unmount.
-f means to run even if "clean" flag is set.
Please reserve -f for that future use case.
What Miklos is saying, and I agree with him, is that fsck.overlay should be
resolve inconsistencies rather then cleanup leftovers that don't bother anyone.
BTW, you should also add a check for "impure" xattr.
There are clear rules about when "impure" should be set - when a pure dir has
entries with "origin" or "redirect" entries inside it - those rule
were NOT honored
since introduction of "redirect" and they were even not fully honored sine
introduction of "origin" ("ovl: mark parent impure on ovl_link()" was
added later)
Missing "impure" will cause wrong d_ino in readdir of impure dir.
[...]
>>
>>> 2) The origin directory should be redirected only once in one layer,
>>> which mean there is only one redirect xattr point to this origin directory in
>>> the specified layer.
>>> 3) A whiteout or an opaque directory with the same name to origin should
>>> exist in the same directory as the redirect directory.
>>>
>>> If not, 1) The redirect xattr is invalid and need to remove 2) One of
>>> the redirect xattr is redundant but not sure which one is, ask user 3)
>>> Create a whiteout device or set opaque xattr to an existing directory if the
>>> parent directory was meregd or remove xattr if not.
>>
>> Hmm, in this case also should ask the user, as it's not clear that the
>> "new" copy resulting from removal of whiteout on upper is the wanted
>> one or the "old" renamed copy.
>>
> Thanks for point this out, do you mean the newly created directory over whiteout
> between old renamed directory? If so, Amir have already pointed out in the first
> iteration and I handled it in current version. Please see:
>
> https://www.spinics.net/lists/linux-unionfs/msg03268.html
>
> Now, fsck will also check dir's redirect xattr for this case, it will add opaque
> xattr only when parent is merged and not redirected.
>
I think what Miklos meant is what I wrote in comment to test 203.
User needs to be asked which dir should be the merge dir and not
assume that the redirected dir is the correct answer.
Amir.
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