Date: Mon, 10 Mar 2003 18:23:18 +1100 From: Peter Jeremy <peterjeremy@optushome.com.au> To: Sean Chittenden <sean@chittenden.org> Cc: arch@FreeBSD.ORG Subject: Re: Should sendfile() to return EAGAIN? [patch] Message-ID: <20030310072318.GA3343@cirb503493.alcatel.com.au> In-Reply-To: <20030309214638.GN79234@perrin.int.nxad.com> References: <20030309135037.GK79234@perrin.int.nxad.com> <Pine.BSF.4.21.0303092026380.85235-100000@is> <20030309214638.GN79234@perrin.int.nxad.com>
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On Sun, Mar 09, 2003 at 01:46:38PM -0800, Sean Chittenden wrote:
>Eh, well, I vacillate on this topic, but there is something to be said
>for source compatibility. Using EAGAIN requires no changes to
>existing code. Returning ENOBUFS does require a change to existing
>code.
I support source compatibility as a guideline but not as a hard-and-fast
rule. This wouldn't be the first time that source compatability has
been broken and won't be the last time. In any case, that last "does"
should be "may" - some applications may no care.
Looking at FreeBSD, the only standard application that uses sendfile(2)
is ftpd(8) - and it doesn't care what the actual errno is. The libc_r
wrapper would need to be modified though and there may be ports that
use sendfile(2).
> By the same token, it seems more correct to me
>to signify to the app that the OS is maxed (ENOBUFS) as opposed to the
>client being maxed (EAGAIN). ::shrug::
The descriptions of the errors (from intro(2)) are:
35 EAGAIN Resource temporarily unavailable. This is a temporary condi-
tion and later calls to the same routine may complete normally.
55 ENOBUFS No buffer space available. An operation on a socket or pipe
was not performed because the system lacked sufficient buffer
space or because a queue was full.
Whilst both errors cover the situation, "ENOBUFS" provides more
information to the caller and I would therefore consider it as the
preferred error.
Peter
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