[PATCH 02/10] block: force an unlimited segment size on queues with a virt boundary

From: Christoph Hellwig <hch@lst.de>
To: axboe@fb.com
Cc: ming.lei@redhat.com, Matias Bjorling <mb@lightnvm.io>,
	linux-block@vger.kernel.org
Subject: [PATCH 02/10] block: force an unlimited segment size on queues with a virt boundary
Date: Mon, 13 May 2019 08:37:46 +0200	[thread overview]
Message-ID: <20190513063754.1520-3-hch@lst.de> (raw)
In-Reply-To: <20190513063754.1520-1-hch@lst.de>

We currently fail to update the front/back segment size in the bio when
deciding to allow an otherwise gappy segement to a device with a
virt boundary.  The reason why this did not cause problems is that
devices with a virt boundary fundamentally don't use segments as we
know it and thus don't care.  Make that assumption formal by forcing
an unlimited segement size in this case.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 block/blk-settings.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/block/blk-settings.c b/block/blk-settings.c
index 3facc41476be..2ae348c101a0 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -310,6 +310,9 @@ void blk_queue_max_segment_size(struct request_queue *q, unsigned int max_size)
 		       __func__, max_size);
 	}
 
+	/* see blk_queue_virt_boundary() for the explanation */
+	WARN_ON_ONCE(q->limits.virt_boundary_mask);
+
 	q->limits.max_segment_size = max_size;
 }
 EXPORT_SYMBOL(blk_queue_max_segment_size);
@@ -742,6 +745,14 @@ EXPORT_SYMBOL(blk_queue_segment_boundary);
 void blk_queue_virt_boundary(struct request_queue *q, unsigned long mask)
 {
 	q->limits.virt_boundary_mask = mask;
+
+	/*
+	 * Devices that require a virtual boundary do not support scatter/gather
+	 * I/O natively, but instead require a descriptor list entry for each
+	 * page (which might not be idential to the Linux PAGE_SIZE).  Because
+	 * of that they are not limited by our notion of "segment size".
+	 */
+	q->limits.max_segment_size = UINT_MAX;
 }
 EXPORT_SYMBOL(blk_queue_virt_boundary);
 
-- 
2.20.1

