On Fri, Jan 25, 2019 at 2:04 PM Amir Goldstein <amir73il@xxxxxxxxx> wrote: > > > > One questions about your patch: > > > Skipping the ovl_change_flags() for upper realfile, that's just a > > > quick hack, right? > > > I'll need to fix this up properly. > > > > Yes. > > > > Speaking of hacks: I don't really like the O_RDWR | O_WRONLY thing. I > > understand why it works, but I think handling it explicitly would be > > much cleaner. > > > > I figured... in fact, it is not at all interesting to propagate f_flags > to copy up helpers, so I was thinking of translating them to simple > copy_up_flags *before* the call to ovl_maybe_copy_up(), i.e.: > > OVL_COPY_UP = 1, > OVL_COPY_UP_DATA = 2, > OVL_COPY_UP_WITH_DATA = 3, Much better. > > > > About the way forward, implementing writepage() should be quite straight forward > > > from this, so I will add write support re-work the series and re-post. > > > > The one issue is, we don't have the open file available from > > writepage(s) like we do in readpage(s). In fact leaving the > > writeback till after close is an important optimization (e.g. > > compilers write temporary files, that are then immediately deleted, so > > no need to actually do any writeback). > > > > That opens some interesting questions about how to do the writeback... > > > > Mmm.... so now using upper page cache for write does sound so bad. > If only we had shared cache pages ;-) > We can treat upper page cache as a vessel for writeback and invalidate > it upon completion, since it is *ours*. > I'll see what I can come up with. Just calling ->writepage() of upper fs won't work, filesystems do preparatory work in ->prepare_write(), etc, and those need the struct file... I don't think we are better off, than calling vfs_write_iter(). Thanks, Miklos
