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SubjectRe: [RFC PATCH v5 06/10] ovl: implement overlayfs' ->write_inode operation
 ---- 在 星期三, 2021-12-01 21:46:10 Jan Kara <jack@suse.cz> 撰写 ----
> On Wed 01-12-21 09:19:17, Amir Goldstein wrote:
> > On Wed, Dec 1, 2021 at 8:31 AM Chengguang Xu <cgxu519@mykernel.net> wrote:
> > > So the final solution to handle all the concerns looks like accurately
> > > mark overlay inode diry on modification and re-mark dirty only for
> > > mmaped file in ->write_inode().
> > >
> > > Hi Miklos, Jan
> > >
> > > Will you agree with new proposal above?
> > >
> >
> > Maybe you can still pull off a simpler version by remarking dirty only
> > writably mmapped upper AND inode_is_open_for_write(upper)?
>
> Well, if inode is writeably mapped, it must be also open for write, doesn't
> it? The VMA of the mapping will hold file open. So remarking overlay inode
> dirty during writeback while inode_is_open_for_write(upper) looks like
> reasonably easy and presumably there won't be that many inodes open for
> writing for this to become big overhead?
>
> > If I am not mistaken, if you always mark overlay inode dirty on ovl_flush()
> > of FMODE_WRITE file, there is nothing that can make upper inode dirty
> > after last close (if upper is not mmaped), so one more inode sync should
> > be enough. No?
>
> But we still need to catch other dirtying events like timestamp updates,
> truncate(2) etc. to mark overlay inode dirty. Not sure how reliably that
> can be done...
>

To be honest I even don't fully understand what's the ->flush() logic in overlayfs.
Why should we open new underlying file when calling ->flush()?
Is it still correct in the case of opening lower layer first then copy-uped case?


Thanks,
Chengguang








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