On 26 Jul, Karl Denninger wrote:
> On 7/26/2016 10:59, Don Lewis wrote:
>> Serf has some code to fall back from IPv4 if an IPv6 and more generally
>> try different addresses on multi-homed servers if connection attempts
>> fail, but it does not work properly on recent versions of FreeBSD. I've
>> tested both recent FreeBSD 10.3-STABLE and HEAD.
>>
>> The way that it is supposed to work is that serf creates a socket, sets
>> it non-blocking, calls connect(), and then passes the fd to poll(). When
>> the connection attempt fails, it expects to see a POLLERR event. The
>> POLLERR event handler will then call getsockopt(fd, SOL_SOCKET,
>> SO_ERROR, &error, ...). If the returned error is ECONNREFUSED or one of
>> a couple of other errors, then serf will move on to the next address.
>>
>> Instead what happens is that serf also(?) sees POLLIN set, which it
>> processes first by calling read(), which returns an ECONNREFUSED error.
>> That not a documented error return from read().
>>
>> An easy way to test this is to truss svn and attempt to do an http
>> checkout from a host that has both IPv6 and IPv4 addresses, but is not
>> listening on port 80. The only connection attempt will be to the IPv6
>> address.
>>
>> socket(PF_INET6,SOCK_STREAM|SOCK_CLOEXEC,6) = 4 (0x4)
>> fcntl(4,F_GETFL,) = 2 (0x2)
>> fcntl(4,F_SETFL,O_NONBLOCK|0x2) = 0 (0x0)
>> setsockopt(0x4,0x6,0x1,0x7fffffffdda4,0x4) = 0 (0x0)
>> gettimeofday({ 1469515046.979461 },0x0) = 0 (0x0)
>> connect(4,{ AF_INET6 [xxxx:xxxx:xxxx:xxxx::xxxx]:80 },28) ERR#36 'Operation
>> now in progress'
>> gettimeofday({ 1469515046.979614 },0x0) = 0 (0x0)
>> kevent(3,{ 4,EVFILT_READ,EV_ADD,0x0,0x0,0x805491300 },1,0x0,0,0x0) = 0 (0x0)
>> kevent(3,{ 4,EVFILT_WRITE,EV_ADD,0x0,0x0,0x805491300 },1,0x0,0,0x0) = 0 (0x0)
>> kevent(3,0x0,0,{ 4,EVFILT_READ,EV_EOF,NOTE_LOWAT|0x3c,0x0,0x805491300
>> 4,EVFILT_WRITE,EV_EOF,NOTE_LOWAT|0x3c,0x8000,0x805491300 },32,{ 0.500000000
>> }) = 2 (0x2)
>> read(4,0x80549c064,8000) ERR#61 'Connection refused'
>> kevent(3,{ 4,EVFILT_READ,EV_DELETE,0x0,0x0,0x0 },1,0x0,0,0x0) = 0 (0x0)
>> kevent(3,{ 4,EVFILT_WRITE,EV_DELETE,0x0,0x0,0x0 },1,0x0,0,0x0) = 0 (0x0)
>> kevent(3,{ 4,EVFILT_READ,EV_DELETE,0x0,0x0,0x0 },1,0x0,0,0x0) ERR#2 'No such
>> file or directory'
>> kevent(3,{ 4,EVFILT_WRITE,EV_DELETE,0x0,0x0,0x0 },1,0x0,0,0x0) ERR#2 'No
>> such file or directory'
>> close(4) = 0 (0x0)
>> close(3) = 0 (0x0)
>> svn: E170013: Unable to connect to a repository at URL ...
>>
>>
>> It looks like it should be possible to patch serf to handle this, but:
>> * Should POLLIN be set for this event?
>>
>> * What errno value should read() return in this case, if it is
>> ECONNREFUSED, then that should be documented.
>>
>>
> This is kinda serious in that the above manifestation in svn effectively
> disables it for those of us that are on IPv4 connections and have no
> provider capability for IPv6 at the present time. When I was running
> 10.2 this was not a problem but as soon as I rolled forward to 11.x it
> showed up.
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=211430
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