Re: [PATCH 2/2] fuse: wait for writeback in fuse_file_fallocate()

[Maxim Patlasov]

08/13/2013 05:23 PM, Brian Foster ÐÐÑÐÑ:
> On 08/13/2013 08:56 AM, Maxim Patlasov wrote:
> > Hi,
> >
> > 08/13/2013 04:05 PM, Brian Foster ÐÐÑÐÑ:
> > > ...
> > > @@ -2478,8 +2516,11 @@ static long fuse_file_fallocate(struct file
> > > *file, int mode, loff_t offset,
> > >          if (lock_inode) {
> > >            mutex_lock(&inode->i_mutex);
> > > -        if (mode & FALLOC_FL_PUNCH_HOLE)
> > > -            fuse_set_nowrite(inode);
> > > +        if (mode & FALLOC_FL_PUNCH_HOLE) {
> > > +            truncate_pagecache_range(inode, offset,
> > > +                         offset + length - 1);
> > > +            fuse_wait_on_writeback(inode, offset, length);
> > > +        }
> > > If this happens to be the first attempt on an fs that doesn't support
> > > fallocate, we'll return -EOPNOTSUPP after having already punched out the
> > > data in the pagecache.
> > Yes, this is unpleasant, but it's not critical, imo. We're returning an
> > error code (even though equal to -EOPNOTSUPP) and a sane application
> > should not make any assumption about current state of the punched
> > region. Also, the application intended to discard given region of the
> > file, so why should it pay care for its content afterwards?
> I agree, though most users probably wouldn't expect that a blatant error
> like EOPNOTSUPP leave the range in a weird state. What's more, it only
> does so if it's the first attempt and behaves more appropriately after
> that.
>
> > > What about replacing the nowrite logic with a
> > > flush (and still followed by your new writeback wait logic) rather than
> > > moving the pagecache truncate?
> > The "flush" you mentioned should firstly flush page cache.
> > invalidate_inode_pages2_range() seems to be a candidate. We definitely
> > cannot ignore error code from it because it can be fuse_launder_page()
> > who got -ENOMEM from fuse_writepage_locked(). In case of err == -ENOMEM,
> > we could safely fail fallocate, but what should we do if it's -EBUSY?
> > Any ideas?
> I was referring to something like filemap_write_and_wait_range(), for
> example. Then continue to use truncate_pagecache_range() as we do today.
> Thoughts

Looks nice. I'll send updated patch after some testing. Thanks a lot for 
the suggestion!

Maxim
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