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From:   David Howells <dhowells@redhat.com>
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References: <20210216102614.GA27555@lst.de> <161340385320.1303470.2392622971006879777.stgit@warthog.procyon.org.uk> <161340390150.1303470.509630287091953754.stgit@warthog.procyon.org.uk>
To:     Christoph Hellwig <hch@lst.de>
Cc:     dhowells@redhat.com, Trond Myklebust <trondmy@hammerspace.com>,
        Anna Schumaker <anna.schumaker@netapp.com>,
        Steve French <sfrench@samba.org>,
        Dominique Martinet <asmadeus@codewreck.org>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Matthew Wilcox <willy@infradead.org>, linux-mm@kvack.org,
        linux-cachefs@redhat.com, linux-afs@lists.infradead.org,
        linux-nfs@vger.kernel.org, linux-cifs@vger.kernel.org,
        ceph-devel@vger.kernel.org, v9fs-developer@lists.sourceforge.net,
        linux-fsdevel@vger.kernel.org, Jeff Layton <jlayton@redhat.com>,
        David Wysochanski <dwysocha@redhat.com>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 04/33] vfs: Export rw_verify_area() for use by cachefiles
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Date:   Tue, 16 Feb 2021 11:55:35 +0000
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Christoph Hellwig <hch@lst.de> wrote:

> > Export rw_verify_area() for so that cachefiles can use it before issuing
> > call_read_iter() and call_write_iter() to effect async DIO operations
> > against the cache.  This is analogous to aio_read() and aio_write().
> 
> I don't think this is the right thing to do.  Instead of calling
> into ->read_iter / ->write_iter directly this should be using helpers.
> 
> What prevents you from using vfs_iocb_iter_read and
> vfs_iocb_iter_write which seem the right level of abstraction for this?

I don't think they existed when I wrote this code.  Should aio use that too,
btw?  I modelled my code on aio_read() and aio_write().

But I can certainly switch to using vfs_iocb_iter_read/write, though the
trivial checks are redundant.  The fsnotify call, I guess I'm missing though
(and is that missing in aio_read/write() also?).

David