netdev - Re: [PATCH net-next v2 3/3] genetlink: fit NLMSG

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Message-ID: <b2e7f22c-6da3-4f48-9940-f3cc1aea2af2@ovn.org>
Date: Thu, 11 Apr 2024 17:39:20 +0200
From: Ilya Maximets <i.maximets@....org>
To: Jakub Kicinski <kuba@...nel.org>
Cc: i.maximets@....org, Eric Dumazet <edumazet@...gle.com>,
 Stefano Brivio <sbrivio@...hat.com>, davem@...emloft.net,
 netdev@...r.kernel.org, pabeni@...hat.com, jiri@...nulli.us,
 idosch@...sch.org, johannes@...solutions.net, fw@...len.de,
 pablo@...filter.org, Martin Pitt <mpitt@...hat.com>,
 Paul Holzinger <pholzing@...hat.com>,
 David Gibson <david@...son.dropbear.id.au>
Subject: Re: [PATCH net-next v2 3/3] genetlink: fit NLMSG_DONE into same
 read() as families

On 4/11/24 17:16, Jakub Kicinski wrote:
> On Thu, 4 Apr 2024 00:52:15 +0200 Ilya Maximets wrote:
>> /usr/sbin/ipsec auto --config ipsec.conf --ctlsocket pluto.ctl \
>>                      --start --asynchronous tun-in-1
>>
>> recvfrom(7, 
>> [
>>   [{nlmsg_len=52, nlmsg_type=RTM_NEWROUTE, nlmsg_flags=NLM_F_MULTI, ...],
>>   ...
>>   [{nlmsg_len=52, nlmsg_type=RTM_NEWROUTE, nlmsg_flags=NLM_F_MULTI, ...],
>>   [{nlmsg_len=20, nlmsg_type=NLMSG_DONE, nlmsg_flags=NLM_F_MULTI, ...]
>> ], 40960, 0, {sa_family=AF_NETLINK, nl_pid=0, nl_groups=00000000}, [12])
>>
>> recvfrom(7, <-- Stuck here forever
> 
> I think we should probably fix this..
> Would you mind sharing the sendmsg() call? Eyeballing rtnl_dump_all() -
> it does seem to coalesce DONE..

Sure, the whole sequence looks like this in strace:

socket(AF_NETLINK, SOCK_DGRAM|SOCK_CLOEXEC, NETLINK_ROUTE) = 7

sendto(7, [
  {
    nlmsg_len=36, nlmsg_type=0x1a /* NLMSG_??? */,
    nlmsg_flags=NLM_F_REQUEST|0x300, nlmsg_seq=0, nlmsg_pid=138040
  },
  "\x02\x20\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x08\x00\x01\x00\x0a\x01\x01\x02"
], 36, 0, NULL, 0) = 36

recvfrom(7, [
 [
   {nlmsg_len=52, nlmsg_type=RTM_NEWROUTE, nlmsg_flags=NLM_F_MULTI, nlmsg_seq=0, nlmsg_pid=138040},
   {rtm_family=AF_INET, rtm_dst_len=0, rtm_src_len=0, rtm_tos=0, rtm_table=RT_TABLE_MAIN,
    rtm_protocol=RTPROT_BOOT, rtm_scope=RT_SCOPE_UNIVERSE, rtm_type=RTN_UNICAST, rtm_flags=0},
   [
     [{nla_len=8, nla_type=RTA_TABLE}, RT_TABLE_MAIN],
     [{nla_len=8, nla_type=RTA_GATEWAY}, inet_addr("10.1.1.2")],
     [{nla_len=8, nla_type=RTA_OIF}, if_nametoindex("p0")]
   ]
 ],
 [
   {nlmsg_len=60, nlmsg_type=RTM_NEWROUTE, nlmsg_flags=NLM_F_MULTI, nlmsg_seq=0, nlmsg_pid=138040},
   {rtm_family=AF_INET, rtm_dst_len=24, rtm_src_len=0, rtm_tos=0, rtm_table=RT_TABLE_MAIN,
    rtm_protocol=RTPROT_KERNEL, rtm_scope=RT_SCOPE_LINK, rtm_type=RTN_UNICAST, rtm_flags=0},
   [
     [{nla_len=8, nla_type=RTA_TABLE}, RT_TABLE_MAIN],
     [{nla_len=8, nla_type=RTA_DST}, inet_addr("10.1.1.0")],
     [{nla_len=8, nla_type=RTA_PREFSRC}, inet_addr("10.1.1.1")],
     [{nla_len=8, nla_type=RTA_OIF}, if_nametoindex("p0")]
   ]
 ],
 [
   {nlmsg_len=60, nlmsg_type=RTM_NEWROUTE, nlmsg_flags=NLM_F_MULTI, nlmsg_seq=0, nlmsg_pid=138040},
   {rtm_family=AF_INET, rtm_dst_len=32, rtm_src_len=0, rtm_tos=0, rtm_table=RT_TABLE_LOCAL,
    rtm_protocol=RTPROT_KERNEL, rtm_scope=RT_SCOPE_HOST, rtm_type=RTN_LOCAL, rtm_flags=0},
   [
     [{nla_len=8, nla_type=RTA_TABLE}, RT_TABLE_LOCAL],
     [{nla_len=8, nla_type=RTA_DST}, inet_addr("10.1.1.1")],
     [{nla_len=8, nla_type=RTA_PREFSRC}, inet_addr("10.1.1.1")],
     [{nla_len=8, nla_type=RTA_OIF}, if_nametoindex("p0")]
   ]
 ],
 [
   {nlmsg_len=60, nlmsg_type=RTM_NEWROUTE, nlmsg_flags=NLM_F_MULTI, nlmsg_seq=0, nlmsg_pid=138040},
   {rtm_family=AF_INET, rtm_dst_len=32, rtm_src_len=0, rtm_tos=0, rtm_table=RT_TABLE_LOCAL,
    rtm_protocol=RTPROT_KERNEL, rtm_scope=RT_SCOPE_LINK, rtm_type=RTN_BROADCAST, rtm_flags=0},
   [
     [{nla_len=8, nla_type=RTA_TABLE}, RT_TABLE_LOCAL],
     [{nla_len=8, nla_type=RTA_DST}, inet_addr("10.1.1.255")],
     [{nla_len=8, nla_type=RTA_PREFSRC}, inet_addr("10.1.1.1")],
     [{nla_len=8, nla_type=RTA_OIF}, if_nametoindex("p0")]
   ]
 ],
 [
   {nlmsg_len=20, nlmsg_type=NLMSG_DONE, nlmsg_flags=NLM_F_MULTI, nlmsg_seq=0, nlmsg_pid=138040}, 0
 ]
], 40960, 0, {sa_family=AF_NETLINK, nl_pid=0, nl_groups=00000000}, [12]) = 252

recvfrom(7,  <unfinished ...>


nlmsg_type=0x1a /* NLMSG_??? */  --> RTM_GETROUTE
nlmsg_flags=NLM_F_REQUEST|0x300  --> NLM_F_REQUEST|NLM_F_DUMP

Best regards, Ilya Maximets.