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[dm-devel] Re: directio path-checker for multipath-tools

On jeu, 2005-08-11 at 16:44 +0200, Hannes Reinecke wrote:
> Hi Christophe,
> I've implemented yet another path checker, based on O_DIRECT.
> Rationale: On S/390 it's possible to activate multipath support for DASD
> devices (called Parallel Access Volume (PAV)). As these are no SCSI
> devices the readsector0 path checker wouldn't work.
> And as this checker is quite generic it'll work for just about anybody.
There seem to be cases where this checker can "hang forever" on failing
paths, and thus block the whole daemon. If I understand correctly the
open() manual, O_DIRECT reads by-design block until the data is sent

If there is a trick to unblock the checker I'd like to learn it, because
as-is this checker is really more dangerous than useful :/

I hit this problem easily by bringing down the network interface
supporting the iSCSI trafic to an sfnet-IET target.


PS: I have to check if other checkers are not affected too. If I
remember we needed some SG infrastructure to let our checkers ask the
kernel to FAILFAST its requests ...

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