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Date: Fri, 20 Apr 2012 10:49:51 -0500 From: Chandra Seetharaman <sekharan@...ibm.com> To: Mike Snitzer <snitzer@...hat.com>, James Bottomley <James.Bottomley@...senPartnership.com> Cc: linux-scsi@...r.kernel.org, Hannes Reinecke <hare@...e.de>, linux-kernel@...r.kernel.org Subject: Re: [RESEND][PATCH] [SCSI] scsi_dh: allow 3rd party multipath drivers to use scsi_dh_detach Mike, First off, sorry for not responding on this earlier. When I saw the original patch, I was thinking it is a generic policy issue, and James would be a better person to make decision on this, and forgot about it. Now only realized that James was waiting on me. I am not very religious either, and agree with James on changing the Changelog. With that change, Acked-by: Chandra Seetharaman <sekharan@...ibm.com> Regards, Chandra On Fri, 2012-04-20 at 19:17 +0400, James Bottomley wrote: > On Fri, 2012-04-20 at 10:45 -0400, Mike Snitzer wrote: > > Allow 3rd party multipath drivers to programatically detach a scsi_dh > > using the scsi_dh_detach() interface. This is as improvement over > > requiring them to write 'detach' to /sys/block/sdX/queue/dh_state > > > > End result is both Linux and 3rd party multipath drivers can coexist > > without compromising Linux's default handling of multipath LUNs. > > > > Linux has suffered from races associated with attaching a scsi_dh to a > > device too late (after an HBA driver has started the SCSI device scan). > > Attaching a scsi_dh too late results in default sense handling that does > > not silently fail IO to passive paths, which creates excessive delays > > and IO errors during normal boot on a system with hundreds of LUNs. > > > > To fix this the appropriate scsi_dh must be attached before the HBA > > driver(s) are even loaded. But some scsi_dh are known to conflict with > > 3rd party multipath drivers (e.g. both scsi_dh_alua and scsi_dh_emc > > conflict with EMC PowerPath). This patch allows 3rd party drivers to > > resolve the conflict by detaching an attached scsi_dh. > > This changelog is a bit misleading, isn't it? > > The basic problem is that binary only third party drivers can't use the > scsi_dh_detach callback because it's GPL only. The only module I know > which suffers this problem is powerpath, is that right? > > So this patch actually relaxes our GPL only policy to allow powerpath to > detach correctly. I really don't like the characterisation in the > current proposed changelog of this being a "third party" problem because > quite a few third party modules actually provide source and are thus GPL > compliant. > > The whole point of GPL only symbols is to make life difficult for binary > modules, so I could just say this might be indicative of the success of > that policy. On the other hand, I'm not going to be religious about > this. If you get the ack of the dh handler maintainer (Chandra > Seetharaman) I'll apply this policy relaxation with a proper changelog > that says what we're doing (allowing powerpath to bind to the symbol). > > James > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-scsi" in > the body of a message to majordomo@...r.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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