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Date: Mon, 19 Mar 2018 14:14:29 -0300
From: Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
To: Stephen Hemminger <stephen@...workplumber.org>
Cc: netdev@...r.kernel.org, Alexander Aring <aring@...atatu.com>,
Jiri Pirko <jiri@...nulli.us>, Jakub Kicinski <kubakici@...pl>
Subject: Re: [PATCH RFC iproute2] libnetlink: allow reading more than one
message from extack
On Mon, Mar 19, 2018 at 09:09:50AM -0700, Stephen Hemminger wrote:
> On Fri, 16 Mar 2018 16:23:09 -0300
> Marcelo Ricardo Leitner <marcelo.leitner@...il.com> wrote:
>
> > This patch introduces support for reading more than one message from
> > extack's and to adjust their level (warning/error) accordingly.
> >
> > Yes, there is a FIXME tag in the callback call for now.
> >
> > Signed-off-by: Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
>
> Make sense, can hold off until kernel supports warnings.
Okay.
>
> > ---
> > lib/libnetlink.c | 55 ++++++++++++++++++++++++++++++++++++++++---------------
> > 1 file changed, 40 insertions(+), 15 deletions(-)
> >
> > diff --git a/lib/libnetlink.c b/lib/libnetlink.c
> > index 928de1dd16d84b7802c06d0a659f5d73e1bbcb4b..7c4c81e11e02ea857888190eb5e7a9e99d159bb3 100644
> > --- a/lib/libnetlink.c
> > +++ b/lib/libnetlink.c
> > @@ -43,9 +43,16 @@ static const enum mnl_attr_data_type extack_policy[NLMSGERR_ATTR_MAX + 1] = {
> > [NLMSGERR_ATTR_OFFS] = MNL_TYPE_U32,
> > };
> >
> > +#define NETLINK_MAX_EXTACK_MSGS 8
>
> Would rather not have fixed maximums
Makes sense. Then it is more forward-compatible in case we increase
that on kernel side later.
>
> > +struct extack_args {
> > + const struct nlattr *msg[NETLINK_MAX_EXTACK_MSGS];
> > + const struct nlattr *offs;
> > + int msg_count;
> > +};
>
> If you put msg[] last in structure, it could be variable length.
It will also require a two-times parsing then because we don't have an
attribute with the number of messages in there and we have to allocate
it with a certain length.
>
> > static int err_attr_cb(const struct nlattr *attr, void *data)
> > {
> > - const struct nlattr **tb = data;
> > + struct extack_args *tb = data;
> > uint16_t type;
> >
> > if (mnl_attr_type_valid(attr, NLMSGERR_ATTR_MAX) < 0) {
> > @@ -60,19 +67,23 @@ static int err_attr_cb(const struct nlattr *attr, void *data)
> > return MNL_CB_ERROR;
> > }
> >
> > - tb[type] = attr;
> > + if (type == NLMSGERR_ATTR_OFFS)
> > + tb->offs = attr;
> > + else if (tb->msg_count < NETLINK_MAX_EXTACK_MSGS)
> > + tb->msg[tb->msg_count++] = attr;
> > return MNL_CB_OK;
> > }
> >
> > /* dump netlink extended ack error message */
> > int nl_dump_ext_ack(const struct nlmsghdr *nlh, nl_ext_ack_fn_t errfn)
> > {
> > - struct nlattr *tb[NLMSGERR_ATTR_MAX + 1] = {};
> > + struct extack_args tb = {};
> > const struct nlmsgerr *err = mnl_nlmsg_get_payload(nlh);
> > const struct nlmsghdr *err_nlh = NULL;
> > unsigned int hlen = sizeof(*err);
> > - const char *msg = NULL;
> > + const char *msg[NETLINK_MAX_EXTACK_MSGS] = {};
> > uint32_t off = 0;
> > + int ret, i;
> >
> > /* no TLVs, nothing to do here */
> > if (!(nlh->nlmsg_flags & NLM_F_ACK_TLVS))
> > @@ -82,14 +93,14 @@ int nl_dump_ext_ack(const struct nlmsghdr *nlh, nl_ext_ack_fn_t errfn)
> > if (!(nlh->nlmsg_flags & NLM_F_CAPPED))
> > hlen += mnl_nlmsg_get_payload_len(&err->msg);
> >
> > - if (mnl_attr_parse(nlh, hlen, err_attr_cb, tb) != MNL_CB_OK)
> > + if (mnl_attr_parse(nlh, hlen, err_attr_cb, &tb) != MNL_CB_OK)
> > return 0;
> >
> > - if (tb[NLMSGERR_ATTR_MSG])
> > - msg = mnl_attr_get_str(tb[NLMSGERR_ATTR_MSG]);
> > + for (i = 0; i < NETLINK_MAX_EXTACK_MSGS && tb.msg[i]; i++)
> > + msg[i] = mnl_attr_get_str(tb.msg[i]);
> >
> > - if (tb[NLMSGERR_ATTR_OFFS]) {
> > - off = mnl_attr_get_u32(tb[NLMSGERR_ATTR_OFFS]);
> > + if (tb.offs) {
> > + off = mnl_attr_get_u32(tb.offs);
> >
> > if (off > nlh->nlmsg_len) {
> > fprintf(stderr,
> > @@ -100,21 +111,35 @@ int nl_dump_ext_ack(const struct nlmsghdr *nlh, nl_ext_ack_fn_t errfn)
> > }
> >
> > if (errfn)
> > - return errfn(msg, off, err_nlh);
> > + return errfn(*msg, off, err_nlh); /* FIXME */
> >
> > - if (msg && *msg != '\0') {
> > + ret = 0;
> > + for (i = 0; i < NETLINK_MAX_EXTACK_MSGS && msg[i]; i++) {
> > bool is_err = !!err->error;
> > + const char *_msg = msg[i];
> > +
> > + /* Message tagging has precedence.
> > + * KERN_WARNING = ASCII Start Of Header ('\001') + '4'
> > + */
> > + if (!strncmp(_msg, "\0014", 2)) {
> > + is_err = false;
> > + _msg += 2;
> > + }
>
> If you are going to have an API that has levels, it must be the same
> as existing syslog kernel log format and maybe even get some code reuse.
It is the same representation already. The magic "\0014" in there is
the same as KERN_WARNING. I'll check how other userspace applications
are dealing with this, as I don't see KERN_WARNING being exported to
userspace.
Thanks,
Marcelo
>
> > + /* But we can't have Error if it didn't fail. */
> > + if (is_err && !err->error)
> > + is_err = 0;
> >
> > fprintf(stderr, "%s: %s",
> > - is_err ? "Error" : "Warning", msg);
> > - if (msg[strlen(msg) - 1] != '.')
> > + is_err ? "Error" : "Warning", _msg);
> > + if (_msg[strlen(_msg) - 1] != '.')
> > fprintf(stderr, ".");
> > fprintf(stderr, "\n");
> >
> > - return is_err ? 1 : 0;
> > + if (is_err)
> > + ret = 1;
> > }
> >
> > - return 0;
> > + return ret;
> > }
> > #else
> > #warning "libmnl required for error support"
>
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