linux-ext4 - Re: Could we get an IOCB_NO_READ

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Message-ID: <20210917110454.GA10535@lst.de>
Date:   Fri, 17 Sep 2021 13:04:54 +0200
From:   Christoph Hellwig <hch@....de>
To:     David Howells <dhowells@...hat.com>
Cc:     Christoph Hellwig <hch@....de>, linux-ext4@...r.kernel.org,
        linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: Could we get an IOCB_NO_READ_HOLE?

On Fri, Sep 17, 2021 at 11:43:59AM +0100, David Howells wrote:
> David Howells <dhowells@...hat.com> wrote:
> 
> > Would it be possible to get an IOCB_NO_READ_HOLE flag that causes a read to
> > either fail entirely if there's a hole in the file or to stop at the hole,
> > possibly returning -ENODATA if the hole is at the front of the file?
> > 
> > Looking at iomap_dio_iter(), IOMAP_HOLE should be enabled in
> > iomap_iter::iomap.type for this?  Is it that simple?
> 
> Actually, that's not the right thing.  How about the attached - at least for
> direct I/O?

This looks pretty reasonable.  We'll just need to make sure to reject
the flag for the many file operations instances that do not support it.