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Re: [Qemu-devel] [PATCH] util: Relax assertion in iov_copy()
From: |
Michael S. Tsirkin |
Subject: |
Re: [Qemu-devel] [PATCH] util: Relax assertion in iov_copy() |
Date: |
Wed, 27 Jul 2016 07:20:08 +0300 |
On Mon, Jul 25, 2016 at 02:43:35PM +0300, Shmulik Ladkani wrote:
> From: Shmulik Ladkani <address@hidden>
>
> In cases where iov_copy() is passed with zero 'bytes' argument and a
> non-zero 'offset' argument, nothing gets copied - as expected.
>
> However since no copy iterations are performed, 'offset' is left
> unaltered, leading to the final assert(offset == 0) to fail.
>
> Relax the assertion: if j (number of dst elements assigned) is zero, no
> need to err.
>
> Only if j!=0 (some dst elements assigned) AND offset!=0 we should err.
>
> Signed-off-by: Shmulik Ladkani <address@hidden>
Reviewed-by: Michael S. Tsirkin <address@hidden>
> ---
> util/iov.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> Flow that led to the assertion was:
> net_tx_pkt_rebuild_payload()
> iov_copy(... , pkt->payload_len)
>
> where pkt->payload_len was correctly calculated to be 0 (a packet
> carrying just ipv4 header, without any payload).
>
> An alternative is to place the below code, early in iov_copy():
> if (!bytes)
> return 0;
>
> diff --git a/util/iov.c b/util/iov.c
> index 003fcce..17de52d 100644
> --- a/util/iov.c
> +++ b/util/iov.c
> @@ -260,7 +260,7 @@ unsigned iov_copy(struct iovec *dst_iov, unsigned int
> dst_iov_cnt,
> bytes -= len;
> offset = 0;
> }
> - assert(offset == 0);
> + assert(j == 0 || offset == 0);
> return j;
> }
>
> --
> 1.9.1
>