Re: [dpdk-dev] [PATCH] kni: fix rte_kni_update_link

[Stephen Hemminger <stephen@networkplumber.org>]

On Thu, 24 Jan 2019 23:47:49 +0300
Igor Ryzhov <iryzhov@nfware.com> wrote:

> After read, file offset must be set to 0 before write.
> Otherwise, the third byte will be overwritten instead of the first.
> 
> Fixes: c6fd54f28c24 ("kni: add function to set link state on kernel interface")
> Cc: stable@dpdk.org
> 
> Signed-off-by: Igor Ryzhov <iryzhov@nfware.com>
> ---
>  lib/librte_kni/rte_kni.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/lib/librte_kni/rte_kni.c b/lib/librte_kni/rte_kni.c
> index 73aeccccf..5899bb14a 100644
> --- a/lib/librte_kni/rte_kni.c
> +++ b/lib/librte_kni/rte_kni.c
> @@ -746,6 +746,12 @@ rte_kni_update_link(struct rte_kni *kni, unsigned int linkup)
>  	}
>  	old_linkup = (old_carrier[0] == '1');
>  
> +	if (lseek(fd, 0, SEEK_SET) == -1) {
> +		RTE_LOG(ERR, KNI, "Failed to change file position: %s.\n", path);
> +		close(fd);
> +		return -1;
> +	}
> +
>  	new_carrier = linkup ? "1" : "0";
>  	ret = write(fd, new_carrier, 1);
>  	if (ret < 1) {

Why not use pwrite() which is atomic?