From owner-cvs-src@FreeBSD.ORG Sun Jun 12 10:30:50 2005 Return-Path: X-Original-To: cvs-src@freebsd.org Delivered-To: cvs-src@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id E6F4416A41C; Sun, 12 Jun 2005 10:30:50 +0000 (GMT) (envelope-from deischen@freebsd.org) Received: from mail.ntplx.net (mail.ntplx.net [204.213.176.10]) by mx1.FreeBSD.org (Postfix) with ESMTP id 9717443D48; Sun, 12 Jun 2005 10:30:50 +0000 (GMT) (envelope-from deischen@freebsd.org) Received: from sea.ntplx.net (sea.ntplx.net [204.213.176.11]) by mail.ntplx.net (8.13.4/8.13.4/NETPLEX) with ESMTP id j5CAUnT6003104; Sun, 12 Jun 2005 06:30:49 -0400 (EDT) Date: Sun, 12 Jun 2005 06:30:49 -0400 (EDT) From: Daniel Eischen X-X-Sender: eischen@sea.ntplx.net To: Alfred Perlstein In-Reply-To: <20050612100708.GK17867@elvis.mu.org> Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Virus-Scanned: by AMaViS and Clam AntiVirus (mail.ntplx.net) Cc: Brian Fundakowski Feldman , src-committers@freebsd.org, cvs-all@freebsd.org, cvs-src@freebsd.org Subject: Re: cvs commit: src/sys/nfsclient nfs_bio.c nfs_vfsops.c nfsargs.h nfsmount.h src/sys/sys buf.h bufobj.h src/sys/kern vfs_bio.c X-BeenThere: cvs-src@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list Reply-To: Daniel Eischen List-Id: CVS commit messages for the src tree List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 12 Jun 2005 10:30:51 -0000 On Sun, 12 Jun 2005, Alfred Perlstein wrote: > * Brian Fundakowski Feldman [050612 01:26] wrote: > > On Sun, Jun 12, 2005 at 01:08:33AM -0700, Alfred Perlstein wrote: > > > > > > Seriously, have you tested what happens to a libc_r app that > > > opens an nfs file F_SYNC? My guess is that it's not pretty. > > > > This code path is related to O_NONBLOCK, not O_FSYNC. O_FSYNC is > > synonymous with the slow fallback path that large transactional block > > now takes, rather than deadlocking. O_NONBLOCK really means that > > whatever they do, they are required to check for EAGAIN. > > To make it perfectly clear. > > If an application linked against libc_r opens a file with O_FSYNC. > Libc_r will set O_NONBLOCK (it does so for each open(2)) > A write on that descriptor will return EAGAIN (to libc_r) > Libc_r will then attempt to select(2) on this decriptor, which > will return "ready" (as do all select(2)'s on disk files) > > The question is: > > Will Libc_r then busy spin? Yes, for the most part. > If so, how many other apps might get screwed just sometimes (over > nfs) because only _half_ of this "solution" is implemented? > > Or is my thinking on this wrong? I think I agree with Alfred. If select() returns ready, then you should be able to write some part of your buffer. Also, anyone using a file descriptor in non-blocking mode should expect short writes and loop until the entire buffer has been written. >From my understanding, disk I/O has always returned ready, then blocked in the kernel if necessary. I think that if we are going to start honoring non-blocking mode for disk I/O (or NFS, whatever), it should be done fully. That means you allow short writes when select() returns ready, and select() doesn't return ready if no data can be written. -- DE