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Date: Thu, 05 Jun 2014 04:51:52 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH v2 6/8] virtio-blk: Use VirtIOBlockReq.in
	to drop VirtIOBlockReq.inhdr
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To: Fam Zheng <famz@redhat.com>, qemu-devel@nongnu.org
Cc: Kevin Wolf <kwolf@redhat.com>, Stefan Hajnoczi <stefanha@redhat.com>

Il 05/06/2014 03:58, Fam Zheng ha scritto:
>      /* Grab inhdr for later */
> -    in_size = iov_size(in_iov, in_num);
> -    if (in_size < sizeof(struct virtio_blk_inhdr)) {
> -        error_report("virtio_blk request inhdr too short");
> -        return -EFAULT;
> -    }
> -    inhdr = g_slice_new(QEMUIOVector);
> -    qemu_iovec_init(inhdr, 1);
> -    qemu_iovec_concat_iov(inhdr, in_iov, in_num,
> -            in_size - sizeof(struct virtio_blk_inhdr),
> -            sizeof(struct virtio_blk_inhdr));
> -    iov_discard_back(in_iov, &in_num, sizeof(struct virtio_blk_inhdr));
> +    inhdr = (void *)in_iov[in_num - 1].iov_base;

This would assume a particular layout for the virtio buffers.  You need 
to add in_iov[in_num - 1].iov_len - sizeof(struct virtio_blk_header).

It's probably also good to ahve an assertion that in_iov[in_num - 
1].iov_len > sizeof(struct virtio_blk_header), and a comment saying that 
the assertion is always true because the struct is only 1-byte long.

Paolo