Date: Thu, 15 Nov 2007 23:38:17 +0100 From: Kris Kennaway <kris@FreeBSD.org> To: Timo Sirainen <tss@iki.fi> Cc: Adam McDougall <mcdouga9@egr.msu.edu>, freebsd-current@FreeBSD.org, Robert Watson <rwatson@FreeBSD.org> Subject: Re: link() not increasing link count on NFS server Message-ID: <473CCA59.8090304@FreeBSD.org> In-Reply-To: <1195132320.6039.135.camel@hurina> References: <20071115074247.GQ37473@egr.msu.edu> <20071115123543.H82897@fledge.watson.org> <1195132320.6039.135.camel@hurina>
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Timo Sirainen wrote: > On Thu, 2007-11-15 at 12:39 +0000, Robert Watson wrote: >>> or Solaris NFS clients. Basically, Timo (cc'ed) came up with a small test >>> case that seems to indicate sometimes a link() call can succeed while the >>> link count of the file will not increase. If this is ran on two FreeBSD >>> clients from the same NFS directory, you will occasionally see "link() >>> succeeded, but link count=1". I've tried both a Netapp and a FreeBSD NFS > .. >> My guess, and this is just a hand-wave, is that the attribute cache in the NFS >> client isn't being forced to refresh, and hence you're getting the old stat >> data back (and perhaps there's no GETATTR on the wire, which might hint at >> this). If you'd like, you can post a link to the pcap capture file and one of >> us can take a look, but I've found NFS RPCs to be surprisingly readable in >> Wireshark so you might find it sheds quite a bit of light. > > Actually the point was that link() returns success even though in > reality it fails. The fstat() was just a workaround to catch this case > and treat link count 1 as if link() had failed with EEXIST. After that I > had no more problems with locking. > > I noticed this first because my dotlocking was failing to lock files > properly. I also added fchown() to flush attribute cache after link() > and before fstat(), it gives the same link count=1 reply. Is it failing (leaving the link count unchanged, when fstat()'ed on the server), or is it just returning a stale link count when the *client* runs fstat()? There is at least one race with the NFS attribute cache that sometimes returns old data to clients when they stat a file that has been recently modified. Kris
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