From: Mike Snitzer <snitzer@redhat.com>
To: Christoph Hellwig <hch@lst.de>
Cc: Jens Axboe <axboe@fb.com>,
linux-block@vger.kernel.org, dm-devel@redhat.com,
linux-scsi@vger.kernel.org
Subject: Re: [PATCH 05/15] dm: remove incomple BLOCK_PC support
Date: Thu, 12 Jan 2017 17:28:45 -0500 [thread overview]
Message-ID: <20170112222845.GA25349@redhat.com> (raw)
In-Reply-To: <20170112080054.GD7567@lst.de>
On Thu, Jan 12 2017 at 3:00am -0500,
Christoph Hellwig <hch@lst.de> wrote:
> On Wed, Jan 11, 2017 at 08:09:37PM -0500, Mike Snitzer wrote:
> > I'm not following your reasoning.
> >
> > dm_blk_ioctl calls __blkdev_driver_ioctl and will call scsi_cmd_ioctl
> > (sd_ioctl -> scsi_cmd_blk_ioctl -> scsi_cmd_ioctl) if DM's underlying
> > block device is a scsi device.
>
> Yes, it it does. But scsi_cmd_ioctl as called from sd_ioctl will
> operate entirely on the SCSI request_queue - dm-mpath will never see
> the BLOCK_PC request generated by it.
I lost sight of the fact that BLOCK_PC requests are sent down via the
normal request submission (and not the ioctl path). So my previous
reply wasn't relevant.
What is "incomplete" about request-based DM's BLOCK_PC support?
This code goes back to when request-based DM multipath was first
introduced via commit cec47e3d4a -- but I've never used the BLOCK_PC
requests for SCSI pass through myself. I don't know who is using
it.. are you aware of some upper layer filesystem or userspace
submission path for these BLOCK_PC requests that they'd be passing
through DM?
I'm also missing how you're saying the new blk-mq request-based DM will
work with your new model. I appreciate that we get the request from the
underlying blk-mq request_queue and it'll be properly sized. But
wouldn't we need to pass data back up for these SCSI pass-through
requests? So wouldn't the top-level multipath request_queue need to
setup cmd_size?
Sorry for the naive questions (that clearly speak to me not
understanding how this aspect of the block and SCSI code work).. but I'd
like to understand where DM will be lacking going forward.
next prev parent reply other threads:[~2017-01-12 22:28 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-01-10 15:06 RFC: split scsi passthrough fields out of struct request Christoph Hellwig
2017-01-10 15:06 ` [PATCH 01/15] virtio_blk: avoid DMA to stack for the sense buffer Christoph Hellwig
2017-01-11 8:26 ` Johannes Thumshirn
2017-01-11 8:43 ` Christoph Hellwig
2017-01-10 15:06 ` [PATCH 02/15] nvme-rdma: fix nvme_rdma_queue_is_ready Christoph Hellwig
2017-01-10 15:06 ` [PATCH 03/15] block: simplify blk_init_allocated_queue Christoph Hellwig
2017-01-10 15:06 ` [PATCH 04/15] block: allow specifying size for extra command data Christoph Hellwig
2017-01-10 15:06 ` [PATCH 05/15] dm: remove incomple BLOCK_PC support Christoph Hellwig
2017-01-12 1:09 ` Mike Snitzer
2017-01-12 8:00 ` Christoph Hellwig
2017-01-12 22:28 ` Mike Snitzer [this message]
2017-01-13 8:14 ` Christoph Hellwig
2017-01-10 15:06 ` [PATCH 06/15] scsi_dh_rdac: switch to scsi_execute_req_flags() Christoph Hellwig
2017-01-10 15:06 ` [PATCH 07/15] scsi_dh_emc: " Christoph Hellwig
2017-01-10 15:06 ` [PATCH 08/15] scsi_dh_hp_sw: " Christoph Hellwig
2017-01-10 15:06 ` [PATCH 09/15] scsi: remove gfp_flags member in scsi_host_cmd_pool Christoph Hellwig
2017-01-10 15:06 ` [PATCH 10/15] scsi: respect unchecked_isa_dma for blk-mq Christoph Hellwig
2017-01-10 15:06 ` [PATCH 11/15] scsi: remove scsi_cmd_dma_pool Christoph Hellwig
2017-01-10 15:06 ` [PATCH 12/15] scsi: remove __scsi_alloc_queue Christoph Hellwig
2017-01-10 15:06 ` [PATCH 13/15] scsi: allocate scsi_cmnd structures as part of struct request Christoph Hellwig
2017-01-10 15:06 ` [PATCH 14/15] block/bsg: move queue creation into bsg_setup_queue Christoph Hellwig
2017-01-11 8:42 ` Johannes Thumshirn
2017-01-11 8:45 ` Christoph Hellwig
2017-01-11 8:56 ` Johannes Thumshirn
2017-01-11 8:59 ` Christoph Hellwig
2017-01-11 8:59 ` Hannes Reinecke
2017-01-11 9:01 ` Christoph Hellwig
2017-01-11 9:37 ` Hannes Reinecke
2017-01-11 22:08 ` Mike Snitzer
2017-01-11 22:01 ` Mike Snitzer
2017-01-12 7:57 ` Christoph Hellwig
2017-01-10 15:06 ` [PATCH 15/15] block: split scsi_request out of struct request Christoph Hellwig
2017-01-12 3:59 ` Jens Axboe
2017-01-11 22:41 ` RFC: split scsi passthrough fields " Mike Snitzer
2017-01-12 7:59 ` Christoph Hellwig
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