From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mike Snitzer Subject: [RESEND][PATCH] [SCSI] scsi_dh: allow 3rd party multipath drivers to use scsi_dh_detach Date: Fri, 20 Apr 2012 10:45:38 -0400 Message-ID: <20120420144538.GB8155@redhat.com> References: <20111215214440.GA17677@redhat.com> <4EF039D5.5010201@suse.de> <20120405144721.GA18437@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20120405144721.GA18437@redhat.com> Sender: linux-kernel-owner@vger.kernel.org To: James.Bottomley@hansenpartnership.com Cc: linux-scsi@vger.kernel.org, Hannes Reinecke , Chandra Seetharaman , linux-kernel@vger.kernel.org List-Id: linux-scsi@vger.kernel.org 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. Signed-off-by: Mike Snitzer Acked-by: Hannes Reinecke Cc: Chandra Seetharaman --- drivers/scsi/device_handler/scsi_dh.c | 2 +- 1 files changed, 1 insertions(+), 1 deletions(-) diff --git a/drivers/scsi/device_handler/scsi_dh.c b/drivers/scsi/device_handler/scsi_dh.c index 23149b9..a550de1 100644 --- a/drivers/scsi/device_handler/scsi_dh.c +++ b/drivers/scsi/device_handler/scsi_dh.c @@ -578,7 +578,7 @@ void scsi_dh_detach(struct request_queue *q) } put_device(&sdev->sdev_gendev); } -EXPORT_SYMBOL_GPL(scsi_dh_detach); +EXPORT_SYMBOL(scsi_dh_detach); static struct notifier_block scsi_dh_nb = { .notifier_call = scsi_dh_notifier