On Thu, Apr 25, 2013 at 12:43:29PM +0200, Florian Westphal wrote:
> We ask for 0xffff copy size, so we need a buffer that can
> hold 0xffff, plus a few more bytes to allow for netlink attributes.
>
> Also, turn off/handle ENOBUFS.
>
> Signed-off-by: Florian Westphal <fw@xxxxxxxxx>
> ---
> examples/nf-queue.c | 38 +++++++++++++++++++++++++-------------
> 1 files changed, 25 insertions(+), 13 deletions(-)
>
> diff --git a/examples/nf-queue.c b/examples/nf-queue.c
> index 7adac21..57ba483 100644
> --- a/examples/nf-queue.c
> +++ b/examples/nf-queue.c
> @@ -1,3 +1,4 @@
> +#include <errno.h>
> #include <stdio.h>
> #include <stdlib.h>
> #include <unistd.h>
> @@ -82,7 +83,8 @@ static int queue_cb(const struct nlmsghdr *nlh, void *data)
>
> int main(int argc, char *argv[])
> {
> - char buf[MNL_SOCKET_BUFFER_SIZE];
> + char *buf;
> + size_t sizeof_buf = 0xffff + 2084;
I think users will appreciate a comment to explain why those black
magic numbers are there ;-). Probably using MNL_SOCKET_BUFFER_SIZE/2
instead of 2084.
> struct nlmsghdr *nlh;
> int ret;
> unsigned int portid, queue_num;
> @@ -105,6 +107,12 @@ int main(int argc, char *argv[])
> }
> portid = mnl_socket_get_portid(nl);
>
> + buf = malloc(sizeof_buf);
> + if (!buf) {
> + perror("allocate receive buffer");
> + exit(EXIT_FAILURE);
> + }
> +
> nlh = nfq_hdr_put(buf, NFQNL_MSG_CONFIG, 0);
> nfq_nlmsg_cfg_put_cmd(nlh, AF_INET, NFQNL_CFG_CMD_PF_UNBIND);
>
> @@ -137,23 +145,27 @@ int main(int argc, char *argv[])
> exit(EXIT_FAILURE);
> }
>
> - ret = mnl_socket_recvfrom(nl, buf, sizeof(buf));
> - if (ret == -1) {
> - perror("mnl_socket_recvfrom");
> - exit(EXIT_FAILURE);
> - }
> - while (ret > 0) {
> - ret = mnl_cb_run(buf, ret, 0, portid, queue_cb, NULL);
> - if (ret < 0){
> - perror("mnl_cb_run");
> - exit(EXIT_FAILURE);
> - }
> + /* ENOBUFS is signalled to userspace when packets were lost
> + * on kernel side. In most cases, userspace isn't interested
> + * in this information, so turn it off.
> + */
> + ret = 1;
> + mnl_socket_setsockopt(nl, NETLINK_NO_ENOBUFS, &ret, sizeof(int));
>
> - ret = mnl_socket_recvfrom(nl, buf, sizeof(buf));
> + for (;;) {
> + ret = mnl_socket_recvfrom(nl, buf, sizeof_buf);
> if (ret == -1) {
> + if (errno == ENOBUFS) /* messages were lost */
Hm, you disabled ENOBUFS errors, right?
> + continue;
> perror("mnl_socket_recvfrom");
> exit(EXIT_FAILURE);
> }
> +
> + ret = mnl_cb_run(buf, ret, 0, portid, queue_cb, NULL);
> + if (ret < 0){
> + perror("mnl_cb_run");
> + exit(EXIT_FAILURE);
> + }
> }
>
> mnl_socket_close(nl);
> --
> 1.7.8.6
>
> --
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