Date: Sat, 23 Aug 2003 11:32:43 -0700 From: Kirk McKusick <mckusick@beastie.mckusick.com> To: "Poul-Henning Kamp" <phk@phk.freebsd.dk> Cc: Paul Saab <ps@yahoo-inc.com> Subject: Re: mksnap_ffs, snapshot issues, again Message-ID: <200308231832.h7NIWiol053778@beastie.mckusick.com> In-Reply-To: Your message of "Sat, 23 Aug 2003 11:01:28 %2B0200." <24772.1061629288@critter.freebsd.dk>
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To: Kirk McKusick <mckusick@mckusick.com> cc: "[iso-8859-2] Branko F. Gračnar" <bfg@noviforum.si>, Paul Saab <ps@yahoo-inc.com>, Robert Watson <rwatson@tislabs.com>, freebsd-current@freebsd.org Subject: Re: mksnap_ffs, snapshot issues, again From: "Poul-Henning Kamp" <phk@phk.freebsd.dk> In-Reply-To: Your message of "Sat, 23 Aug 2003 01:32:38 PDT." Date: Sat, 23 Aug 2003 11:01:28 +0200 X-ASK-Info: Whitelist match In message <200308230832.h7N8Wcol050681@beastie.mckusick.com>, Kirk McKusick writes: >But, to get to the problem that you are having with accessing your >filesystem. The problem is that although the filesystem is only >locked briefly, the snapshot file is locked for the entire 48 minutes. >Thus, if you touch the snapshot file (by for example doing a "stat" >on it), then the process doing the stat will hang for 48 minutes. Isn't there some way we can loosen this aspect up ? Either by having stat know about it and return approximate info or simply by failing ? (I pressume that making the sleep interruptible would break all sorts of standards) -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 phk@FreeBSD.ORG | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe The race to the root problem in general could be largely solved by changing lookup (VOP_LOOKUP really) to release the lock that it holds on the directory before blocking on the next component in the case where it is doing a lookup without intent to create. If we did this, then a single locked node would have lookups pile up on itself, but could not cascade to the root. A related change would be to do an interruptable locking request on the node so that if one did an `ls -l foo' where foo was say a locked snapshot, it would be possible to interrupt it. ~Kirk
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