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

[Christophe Varoqui <christophe varoqui free fr>]

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
back.

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.

Regards,
cvaroqui

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 ...