linux-kernel - Re: [PATCH 07/30] aio: add delayed cancel support

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Message-ID: <20180329085305.GA22215@lst.de>
Date:   Thu, 29 Mar 2018 10:53:05 +0200
From:   Christoph Hellwig <hch@....de>
To:     Al Viro <viro@...IV.linux.org.uk>
Cc:     Christoph Hellwig <hch@....de>, Avi Kivity <avi@...lladb.com>,
        linux-aio@...ck.org, linux-fsdevel@...r.kernel.org,
        netdev@...r.kernel.org, linux-api@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 07/30] aio: add delayed cancel support

On Wed, Mar 28, 2018 at 05:35:26PM +0100, Al Viro wrote:
> >  	ret = vfs_fsync(req->file, req->datasync);
> > -	fput(req->file);
> > -	aio_complete(container_of(req, struct aio_kiocb, fsync), ret, 0);
> > +	if (aio_complete(iocb, ret, 0, 0))
> > +		fput(file);
> 
> IDGI.
> 	1) can aio_complete() ever return false here?

It won't.  But sometimes checking the return value and sometimes not
seems like a bad pattern.

> 	2) do we ever have aio_kiocb that would not have an associated
> struct file * that needs to be dropped on successful aio_complete()?  AFAICS,
> rw, fsync and poll variants all have one, and I'm not sure what kind of
> async IO *could* be done without an opened file.

All have a file assoiated at least right now.  As mentioned last time
finding a struct to pass that file would be rather annoying, so we'd either
have to pass it explicitly, or do something nasty like duplicating the
pointer in the aio_kiocb in addition to struct kiocb.  Which might not
be that bad after all, as it would only bloat the aio_kiocb and not
struct kiocb used on stack all over.