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Date: Mon, 18 Sep 2017 09:55:05 +0200
From: Michal Kubecek <mkubecek@...e.cz>
To: Hangbin Liu <liuhangbin@...il.com>
Cc: netdev@...r.kernel.org,
Stephen Hemminger <stephen@...workplumber.org>,
Phil Sutter <phil@....cc>
Subject: Re: [PATCHv2 iproute2 1/2] lib/libnetlink: re malloc buff if size is
not enough
On Wed, Sep 13, 2017 at 05:59:39PM +0800, Hangbin Liu wrote:
> With commit 72b365e8e0fd ("libnetlink: Double the dump buffer size")
> we doubled the buffer size to support more VFs. But the VFs number is
> increasing all the time. Some customers even use more than 200 VFs now.
>
> We could not double it everytime when the buffer is not enough. Let's just
> not hard code the buffer size and malloc the correct number when running.
>
> Introduce function rtnl_recvmsg() to always return a newly allocated buffer.
> The caller need to free it after using.
>
> Signed-off-by: Hangbin Liu <liuhangbin@...il.com>
> Signed-off-by: Phil Sutter <phil@....cc>
> ---
> lib/libnetlink.c | 112 ++++++++++++++++++++++++++++++++++++++-----------------
> 1 file changed, 78 insertions(+), 34 deletions(-)
>
> diff --git a/lib/libnetlink.c b/lib/libnetlink.c
> index be7ac86..e3fa7cf 100644
> --- a/lib/libnetlink.c
> +++ b/lib/libnetlink.c
> @@ -402,6 +402,62 @@ static void rtnl_dump_error(const struct rtnl_handle *rth,
> }
> }
>
> +static int rtnl_recvmsg(int fd, struct msghdr *msg, char **answer)
> +{
> + struct iovec *iov;
> + int len = -1, buf_len = 32768;
> + char *bufp, *buf = NULL;
> +
> + int flag = MSG_PEEK | MSG_TRUNC;
> +
> +realloc:
> + bufp = realloc(buf, buf_len);
> +
> + if (bufp == NULL) {
> + fprintf(stderr, "malloc error: not enough buffer\n");
> + free(buf);
> + return -ENOMEM;
> + }
> + buf = bufp;
> + iov = msg->msg_iov;
> + iov->iov_base = buf;
> + iov->iov_len = buf_len;
> +
> +recv:
> + len = recvmsg(fd, msg, flag);
> +
> + if (len < 0) {
> + if (errno == EINTR || errno == EAGAIN)
> + goto recv;
> + fprintf(stderr, "netlink receive error %s (%d)\n",
> + strerror(errno), errno);
free(buf);
> + return len;
Maybe we should return -errno (saved before calling fprintf()) to be
consistent.
> + }
> +
> + if (len == 0) {
> + fprintf(stderr, "EOF on netlink\n");
free(buf);
> + return -ENODATA;
> + }
> +
> + if (len > buf_len) {
> + buf_len = len;
> + flag = 0;
> + goto realloc;
> + }
> +
> + if (flag != 0) {
> + flag = 0;
> + goto recv;
> + }
This means that even if the default buffer size is sufficient (which
should be most of the time) we make the kernel copy the message to
userspace again. Perhaps we could just call recvmsg() with zero length
to discard the message from the queue in this case. But it's not really
a big problem, I guess.
> +
> + if (answer)
> + *answer = buf;
> + else
> + free(buf);
> +
> + return len;
> +}
> +
> int rtnl_dump_filter_l(struct rtnl_handle *rth,
> const struct rtnl_dump_filter_arg *arg)
> {
> @@ -413,31 +469,18 @@ int rtnl_dump_filter_l(struct rtnl_handle *rth,
> .msg_iov = &iov,
> .msg_iovlen = 1,
> };
> - char buf[32768];
> + char *buf;
> int dump_intr = 0;
>
> - iov.iov_base = buf;
> while (1) {
> int status;
> const struct rtnl_dump_filter_arg *a;
> int found_done = 0;
> int msglen = 0;
>
> - iov.iov_len = sizeof(buf);
> - status = recvmsg(rth->fd, &msg, 0);
> -
> - if (status < 0) {
> - if (errno == EINTR || errno == EAGAIN)
> - continue;
> - fprintf(stderr, "netlink receive error %s (%d)\n",
> - strerror(errno), errno);
> - return -1;
> - }
> -
> - if (status == 0) {
> - fprintf(stderr, "EOF on netlink\n");
> - return -1;
> - }
> + status = rtnl_recvmsg(rth->fd, &msg, &buf);
> + if (status < 0)
> + return status;
>
> if (rth->dump_fp)
> fwrite(buf, 1, NLMSG_ALIGN(status), rth->dump_fp);
> @@ -462,8 +505,10 @@ int rtnl_dump_filter_l(struct rtnl_handle *rth,
>
> if (h->nlmsg_type == NLMSG_DONE) {
> err = rtnl_dump_done(h);
> - if (err < 0)
> + if (err < 0) {
> + free(buf);
> return -1;
> + }
>
> found_done = 1;
> break; /* process next filter */
> @@ -471,19 +516,23 @@ int rtnl_dump_filter_l(struct rtnl_handle *rth,
>
> if (h->nlmsg_type == NLMSG_ERROR) {
> rtnl_dump_error(rth, h);
> + free(buf);
> return -1;
> }
>
> if (!rth->dump_fp) {
> err = a->filter(&nladdr, h, a->arg1);
> - if (err < 0)
> + if (err < 0) {
> + free(buf);
> return err;
> + }
> }
>
> skip_it:
> h = NLMSG_NEXT(h, msglen);
> }
> }
> + free(buf);
We only free the last buffer returned by rtnl_recvmsg() this way. IMHO
this free(buf) should be moved inside the loop.
>
> if (found_done) {
> if (dump_intr)
> @@ -543,7 +592,7 @@ static int __rtnl_talk(struct rtnl_handle *rtnl, struct nlmsghdr *n,
> .msg_iov = &iov,
> .msg_iovlen = 1,
> };
> - char buf[32768] = {};
> + char *buf;
>
> n->nlmsg_seq = seq = ++rtnl->seq;
>
> @@ -556,22 +605,12 @@ static int __rtnl_talk(struct rtnl_handle *rtnl, struct nlmsghdr *n,
> return -1;
> }
>
> - iov.iov_base = buf;
> while (1) {
> - iov.iov_len = sizeof(buf);
> - status = recvmsg(rtnl->fd, &msg, 0);
> + status = rtnl_recvmsg(rtnl->fd, &msg, &buf);
> +
> + if (status < 0)
> + return status;
>
> - if (status < 0) {
> - if (errno == EINTR || errno == EAGAIN)
> - continue;
> - fprintf(stderr, "netlink receive error %s (%d)\n",
> - strerror(errno), errno);
> - return -1;
> - }
> - if (status == 0) {
> - fprintf(stderr, "EOF on netlink\n");
> - return -1;
> - }
> if (msg.msg_namelen != sizeof(nladdr)) {
> fprintf(stderr,
> "sender address length == %d\n",
> @@ -585,6 +624,7 @@ static int __rtnl_talk(struct rtnl_handle *rtnl, struct nlmsghdr *n,
> if (l < 0 || len > status) {
> if (msg.msg_flags & MSG_TRUNC) {
> fprintf(stderr, "Truncated message\n");
> + free(buf);
> return -1;
> }
> fprintf(stderr,
> @@ -611,6 +651,7 @@ static int __rtnl_talk(struct rtnl_handle *rtnl, struct nlmsghdr *n,
> if (answer)
> memcpy(answer, h,
> MIN(maxlen, h->nlmsg_len));
> + free(buf);
> return 0;
> }
>
> @@ -619,12 +660,14 @@ static int __rtnl_talk(struct rtnl_handle *rtnl, struct nlmsghdr *n,
> rtnl_talk_error(h, err, errfn);
>
> errno = -err->error;
> + free(buf);
> return -1;
> }
>
> if (answer) {
> memcpy(answer, h,
> MIN(maxlen, h->nlmsg_len));
> + free(buf);
> return 0;
> }
>
> @@ -633,6 +676,7 @@ static int __rtnl_talk(struct rtnl_handle *rtnl, struct nlmsghdr *n,
> status -= NLMSG_ALIGN(len);
> h = (struct nlmsghdr *)((char *)h + NLMSG_ALIGN(len));
> }
> + free(buf);
Same as above.
>
> if (msg.msg_flags & MSG_TRUNC) {
> fprintf(stderr, "Message truncated\n");
> --
> 2.5.5
>
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