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SubjectRe: [PATCH 1/3] fs: allow short direct-io reads to be completed via buffered IO
On Tue, May 04, 2010 at 10:14:18AM +1000, Dave Chinner wrote:
> On Mon, May 03, 2010 at 01:27:02PM -0400, Josef Bacik wrote:
> > This is similar to what already happens in the write case. If we have a short
> > read while doing O_DIRECT, instead of just returning, fallthrough and try to
> > read the rest via buffered IO. BTRFS needs this because if we encounter a
> > compressed or inline extent during DIO, we need to fallback on buffered. If the
> > extent is compressed we need to read the entire thing into memory and
> > de-compress it into the users pages. I have tested this with fsx and everything
> > works great. Thanks,
>
> Won't this mean that any direct IO read that spans EOF (i.e. get a
> short read) now attempt a buffered IO (that will fail) before returning?
>

Hmm yeah you are right. What would be an acceptable way to avoid this, do a

if (retval || !count || ppos >= i_size_read(inode))
goto out;
type thing? Thanks,

Josef


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