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Date: Wed, 30 Mar 2011 20:55:46 +0200
From: Christoph Hellwig <hch@lst.de>
Subject: Re: [Qemu-devel] virtio-blk.c handling of i/o which is not a 512
	multiple
Message-ID: <20110330185546.GA26589@lst.de>
References: <loom.20110330T104712-100@post.gmane.org>
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To: Conor Murphy <conor_murphy_virt@hotmail.com>
Cc: qemu-devel@nongnu.org

On Wed, Mar 30, 2011 at 08:48:18AM +0000, Conor Murphy wrote:
> Is there a requirement for virtio-blk guest drivers that all i/o requests are
> sized in multiples of 512 bytes?

Yes, like for any other block driver.  Of course this should not actually
crash qemu, but rather fail the request.

Does the patch below give you a correct error report?


Index: qemu/hw/virtio-blk.c
===================================================================
--- qemu.orig/hw/virtio-blk.c	2011-03-30 20:46:10.268665534 +0200
+++ qemu/hw/virtio-blk.c	2011-03-30 20:49:45.655247322 +0200
@@ -290,6 +290,10 @@ static void virtio_blk_handle_write(Virt
         virtio_blk_rw_complete(req, -EIO);
         return;
     }
+    if (req->qiov.size % req->dev->conf->logical_block_size) {
+        virtio_blk_rw_complete(req, -EIO);
+        return;
+    }
 
     if (mrb->num_writes == 32) {
         virtio_submit_multiwrite(req->dev->bs, mrb);
@@ -317,6 +321,10 @@ static void virtio_blk_handle_read(VirtI
         virtio_blk_rw_complete(req, -EIO);
         return;
     }
+    if (req->qiov.size % req->dev->conf->logical_block_size) {
+        virtio_blk_rw_complete(req, -EIO);
+        return;
+    }
 
     acb = bdrv_aio_readv(req->dev->bs, sector, &req->qiov,
                          req->qiov.size / BDRV_SECTOR_SIZE,