linux-kernel - [PATCH] virtio_blk: fix incorrect message when disk is resized

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Message-Id: <20170726143223.2769-1-stefanha@redhat.com>
Date:   Wed, 26 Jul 2017 15:32:23 +0100
From:   Stefan Hajnoczi <stefanha@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     Jason Wang <jasowang@...hat.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        virtualization@...ts.linux-foundation.org,
        Stefan Hajnoczi <stefanha@...hat.com>
Subject: [PATCH] virtio_blk: fix incorrect message when disk is resized

The message printed on disk resize is incorrect.  The following is
printed when resizing to 2 GiB:

  $ truncate -s 1G test.img
  $ qemu -device virtio-blk-pci,logical_block_size=4096,...
  (qemu) block_resize drive1 2G

  virtio_blk virtio0: new size: 4194304 4096-byte logical blocks (17.2 GB/16.0 GiB)

The virtio_blk capacity config field is in 512-byte sector units
regardless of logical_block_size as per the VIRTIO specification.
Therefore the message should read:

  virtio_blk virtio0: new size: 524288 4096-byte logical blocks (2.15 GB/2.0 GiB)

Note that this only affects the printed message.  Thankfully the actual
block device has the correct size because the block layer expects
capacity in sectors.

Signed-off-by: Stefan Hajnoczi <stefanha@...hat.com>
---
 drivers/block/virtio_blk.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index 4e02aa5fdac0..69a2d1748743 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -381,6 +381,7 @@ static void virtblk_config_changed_work(struct work_struct *work)
 	struct request_queue *q = vblk->disk->queue;
 	char cap_str_2[10], cap_str_10[10];
 	char *envp[] = { "RESIZE=1", NULL };
+	unsigned long long nblocks;
 	u64 capacity;
 
 	/* Host must always specify the capacity. */
@@ -393,16 +394,19 @@ static void virtblk_config_changed_work(struct work_struct *work)
 		capacity = (sector_t)-1;
 	}
 
-	string_get_size(capacity, queue_logical_block_size(q),
+	nblocks = DIV_ROUND_UP_ULL(capacity, queue_logical_block_size(q) >> 9);
+
+	string_get_size(nblocks, queue_logical_block_size(q),
 			STRING_UNITS_2, cap_str_2, sizeof(cap_str_2));
-	string_get_size(capacity, queue_logical_block_size(q),
+	string_get_size(nblocks, queue_logical_block_size(q),
 			STRING_UNITS_10, cap_str_10, sizeof(cap_str_10));
 
 	dev_notice(&vdev->dev,
-		  "new size: %llu %d-byte logical blocks (%s/%s)\n",
-		  (unsigned long long)capacity,
-		  queue_logical_block_size(q),
-		  cap_str_10, cap_str_2);
+		   "new size: %llu %d-byte logical blocks (%s/%s)\n",
+		   nblocks,
+		   queue_logical_block_size(q),
+		   cap_str_10,
+		   cap_str_2);
 
 	set_capacity(vblk->disk, capacity);
 	revalidate_disk(vblk->disk);
-- 
2.13.3