Messages in this thread Patch in this message | | | From | Rusty Russell <> | Subject | Re: [PATCH] virtio-blk: fix minimum number of S/G elements | Date | Wed, 26 May 2010 17:33:28 +0930 |
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On Tue, 25 May 2010 09:47:54 pm Christoph Hellwig wrote: > > 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>
Seems reasonable: we might as well ignore it if device is obviously talking crap.
However, the result is awkward (we assign err then don't use it), and assumes that sg_elems isn't touched on error (true at the moment).
Prefer this:
Subject: virtio-blk: fix minimum number of S/G elements Date: Tue, 25 May 2010 14:17:54 +0200 From: Christoph Hellwig <hch@lst.de>
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)
diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c --- a/drivers/block/virtio_blk.c +++ b/drivers/block/virtio_blk.c @@ -298,7 +298,9 @@ static int __devinit virtblk_probe(struc 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. */
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