linux-ext4 - Re: [PATCH 11/17] iomap: assign current->backing_dev_info in iomap_file_buffered

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Date:   Mon, 24 Apr 2023 08:22:20 +0200
From:   Christoph Hellwig <hch@....de>
To:     "Darrick J. Wong" <djwong@...nel.org>
Cc:     Christoph Hellwig <hch@....de>, Jens Axboe <axboe@...nel.dk>,
        Miklos Szeredi <miklos@...redi.hu>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Howells <dhowells@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        linux-block@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        ceph-devel@...r.kernel.org, linux-ext4@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net, cluster-devel@...hat.com,
        linux-xfs@...r.kernel.org, linux-nfs@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 11/17] iomap: assign current->backing_dev_info in
 iomap_file_buffered_write

On Sun, Apr 23, 2023 at 11:18:25PM -0700, Darrick J. Wong wrote:
> > @@ -876,8 +877,11 @@ iomap_file_buffered_write(struct kiocb *iocb, struct iov_iter *i,
> >  	if (iocb->ki_flags & IOCB_NOWAIT)
> >  		iter.flags |= IOMAP_NOWAIT;
> >  
> > +	current->backing_dev_info = inode_to_bdi(iter.inode);
> 
> Dumb question from me late on a Sunday night, but does the iomap_unshare
> code need to set this too?  Since it works by dirtying pagecache folios
> without actually changing the contents?

A very good question that I have no answer for.  The
current->backing_dev_info mechanism confuses the heck out of me and
appears basically undocumented.