Date: Sun, 12 Jun 2005 03:07:08 -0700 From: Alfred Perlstein <alfred@freebsd.org> To: Brian Fundakowski Feldman <green@freebsd.org> Cc: cvs-src@freebsd.org, src-committers@freebsd.org, cvs-all@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 Message-ID: <20050612100708.GK17867@elvis.mu.org> In-Reply-To: <20050612082612.GF66188@green.homeunix.org> References: <200506102350.j5ANofFM008212@repoman.freebsd.org> <20050611034930.GY17867@elvis.mu.org> <20050611064956.GC66188@green.homeunix.org> <20050611141021.GD17867@elvis.mu.org> <20050611170425.GD66188@green.homeunix.org> <20050611174617.GE17867@elvis.mu.org> <20050611212534.GE66188@green.homeunix.org> <20050612080833.GJ17867@elvis.mu.org> <20050612082612.GF66188@green.homeunix.org>
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* Brian Fundakowski Feldman <green@freebsd.org> [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? 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? -- - Alfred Perlstein - email: bright@mu.org cell: 408-480-4684
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