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SubjectRe: [PATCH 0/7] overlay filesystem: request for inclusion

Miklos Szeredi:
> st_nlink==1 for directories is widely accepted way of saying that the
> number of subdirectories is unknown. Various filesystems already do
> this, and versions of GNU utils that I have come across accept it.

When the upperdir is tmpfs, the link count of the directories in it will
not be 1, won't it?

> > - If I remember correctly, Valerie Aurora has pointed out that
> > open(O_RDONLY) + fchmod() will work correctly in UnionMount.
> > It is true in overlayfs too?
> Neither union-mounts nor overlayfs can handle this case.

Oh, I meant "will work NOT correctly". Sorry.

> I hadn't thought about this case, so overlayfs would modify the lower
> filesystem in that case, which is a no-no.
> Following patch fixes this and return -EROFS for the above case. I also
> updated the non-standard section in the docs.

Hmm, such changes to mnt_flags looks slightly rude to me. Do we have to
consider about these?
- there may exist files opened as RW on the lower.
- when overlayfs is unmounted, it should restore the original mnt_flags.
- (there may exist more...)

If overlayfs doesn't expect the lower mounted as RW, then it might be
better to reject it simply at mounting.

J. R. Okajima

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