linux-kernel - Re: [PATCH] aio: Support read/write with non-iter file-ops

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Date:   Thu, 18 Jul 2019 16:43:52 -0700
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     Benjamin LaHaise <bcrl@...ck.org>, linux-fsdevel@...r.kernel.org,
        linux-aio@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] aio: Support read/write with non-iter file-ops

On Thu 18 Jul 16:17 PDT 2019, Al Viro wrote:

> On Thu, Jul 18, 2019 at 04:10:54PM -0700, Bjorn Andersson wrote:
> > Implement a wrapper for aio_read()/write() to allow async IO on files
> > not implementing the iter version of read/write, such as sysfs. This
> > mimics how readv/writev uses non-iter ops in do_loop_readv_writev().
> 
> IDGI.  How would that IO manage to be async?  And what's the point
> using aio in such situations in the first place?

The point is that an application using aio to submit io operations on a
set of files, can use the same mechanism to read/write files that
happens to be implemented by driver only implementing read/write (not
read_iter/write_iter) in the registered file_operations struct, such as
kernfs.

In this particular case I have a sysfs file that is accessing hardware
and hence will block for a while and using this patch I can io_submit()
a write and handle the completion of this in my normal event loop.

Each individual io operation will be just as synchronous as the current
iter-based mechanism - for the drivers that implement that.

Regards,
Bjorn