linux-kernel - Re: sendfile and EAGAIN

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Date:	Sat, 02 Mar 2013 19:53:47 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Ulrich Drepper <drepper@...il.com>
CC:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Al Viro <viro@...iv.linux.org.uk>
Subject: Re: sendfile and EAGAIN

On 02/25/2013 09:22 AM, Ulrich Drepper wrote:
> When using sendfile with a non-blocking output file descriptor for a
> socket the operation can cause a partial write because of capacity
> issues.  This is nothing critical and the operation could resume after
> the output queue is cleared.  The problem is: there is no way to
> determine where to resume.
> 
> The system call just returns -EAGAIN without any further indication.
> The caller doesn't know what to resend.

This is IMO just a bug.  EAGAIN should only be used in the zero-byte
case and in other cases it should return the number of bytes
transferred, just like all the read/write system calls.

This was clearly also the intent.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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