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virtio-blk: fix minimum number of S/G elements 

We need at least one S/G element to operate properly, as does the block
layer which increments it to one anyway.  We hit this due to a qemu
bug which advertises a sg_elements of 0 under some circumstances.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au> (tweaked logic)
This commit is contained in:
Christoph Hellwig 2010-05-25 14:17:54 +02:00 committed by Rusty Russell
parent aef4b9aaae
commit a5b365a652
1 changed files with 3 additions and 1 deletions
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4
drivers/block/virtio_blk.c
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@ -298,7 +298,9 @@ static int __devinit virtblk_probe(struct virtio_device *vdev)
err = virtio_config_val(vdev, VIRTIO_BLK_F_SEG_MAX,
offsetof(struct virtio_blk_config, seg_max),
&sg_elems);
if (err)
/* We need at least one SG element, whatever they say. */
if (err || !sg_elems)
sg_elems = 1;
/* We need an extra sg elements at head and tail. */