Thanks for the review Ben.
Please see inline for few comments.
Numan
On Wed, Mar 8, 2017 at 10:22 PM, Ben Pfaff <b...@ovn.org> wrote:
> On Fri, Feb 10, 2017 at 08:02:15PM +0530, nusid...@redhat.com wrote:
> > From: Numan Siddique <nusid...@redhat.com>
> >
> > This patch adds a new OVN action 'dns_lkup' to support native DNS.
> > ovn-controller parses this action and adds a NXT_PACKET_IN2
> > OF flow with 'pause' flag set.
> >
> > A new table 'DNS' is added in the SB DB to look up and resolve
> > the DNS queries. When a valid DNS packet is received by
> > ovn-controller, it looks up the DNS name in the 'DNS' table
> > and if successful, it frames a DNS reply, resumes the packet
> > and stores 1 in the 1-bit subfield. If the packet is invalid
> > or cannot be resolved, it resumes the packet without any
> > modifications and stores 0 in the 1-bit subfield.
> >
> > reg0[4] = dns_lkup(); next;
> >
> > An upcoming patch will use this action and adds logical flows.
> >
> > Signed-off-by: Numan Siddique <nusid...@redhat.com>
>
> Thank you for working on this!
>
> Would you mind spelling out "lookup"? I don't know of a reason to
> abbreviate to "lkup" here. It's always a little easier to read a full
> word.
>
Done.
>
> I understand why ovn-trace can't do a proper lookup. I think that it
> should at least set the destination bit to 0 and put a message into the
> trace about it.
>
>
In the v2 patch (which I will send shortly), I have put a message "as no
implemented". I think it should be possible for ovn-trace to support
"dns_lookup". I will look into it as a follow patch. Please let me know if
you have any concerns which you want me to handle in this patch.
ovn-sb.xml should document the new action.
>
>
Done.
> The documentation for the DNS table in ovn-sb.xml talks about VIFs. I
> don't think that name resolution is limited to names for VIFs or even
> specialized for VIFs.
>
>
Corrected it.
> I don't think that struct dns_header needs to be marked "packed",
> because I don't see anything in the struct that the compiler would pad.
>
> Done.
> In the DNS table, I wonder whether there is an advantage to the proposed
> approach of having separate columns for IPv4 and IPv6 addresses. It
> might be more user friendly to just have a single column that can
> contain both kinds of addresses.
>
> Done. Just one column in v2.
> In the DNS table, I wonder about the "hostname" and "fqdn" columns. I
> thought that DNS servers always worked in terms of FQDN, and that it was
> the DNS clients that were responsible for transforming a hostname to an
> FQDN (by appending their own domain name).
>
>
Agree. I have dropped "fqdn" column in v2.
> I guess that, if "hostname" and "fqdn" both make sense, then there
> should be a database index on each of them, like this, in
> ovn-sb.ovsschema:
>
> "indexes": [["hostname", "datapath"], ["fqdn", "datapath"]],
>
> I don't see anything that validates that dns_lkup() is called on a UDP
> packet. One way to do that would be to make udp a prereq for
> dns_lkup(), e.g.:
>
Done.
>
> @@ -1727,6 +1727,7 @@ parse_dns_lkup(struct action_context *ctx, const
> struct expr_field *dst,
> return;
> }
> dl->dst = *dst;
> + add_prerequisite(ctx, "udp");
> }
>
> static void
>
> This patch causes some warnings from Clang:
>
> ../ovn/controller/pinctrl.c:741:35: error: cast from 'uint8_t *' (aka
> 'unsigned char *') to 'ovs_be16 *' (aka 'unsigned short *') increases
> required alignment from 1 to 2 [-Werror,-Wcast-align]
> /usr/include/netinet/in.h:403:33: note: expanded from macro 'ntohs'
> /usr/include/i386-linux-gnu/bits/byteswap-16.h:27:62: note: expanded
> from macro '__bswap_16'
>
> I think that the cast in question is OK, so I would change it to an
> ALIGNED_CAST to suppress the warning.
>
>
Done.
> In pinctrl_handle_dns_lkup() here, I would drop the ntohs() for checking
> that a value is nonzero:
>
> if (!ntohs(in_dns_header->qdcount)) {
>
> Done
> Here, I think that for safety the operands of && should be in the
> opposite order:
>
> while (in_dns_data[idx] && (in_dns_data + idx) < end) {
>
>
Done
> I don't see anything here that checks for reading beyond the end of the
> data:
>
> uint8_t label_len = in_dns_data[idx++];
> for (uint8_t i = 0; i < label_len; i++) {
> ds_put_char(&hostname, in_dns_data[idx++]);
> }
>
>
Done.
> I think it would be good to declare macros or enums for query types, or
> at least for the supported A, AAAA, and ANY query types.
>
>
Done.
> Thanks,
>
> Ben.
>
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