s3:smbd multichannel refresh network information

To maintain SMB Multichannel, windows client might periodically query with FSCTL_QUERY_NETWORK_INTERFACE_INFO to get SMB server's network information, in my case windows server 2022 would do this every 10 minutes (600 seconds).

Consider a scenario: the network information might have changed between these queries, some become link down, new interface is link up, network speed is changed, and etc. So far smbd might not aware of these changes and still report out-of-date network information to windows client, until we manually send a SIGHUP to smbd in order to trigger load_interfaces(): smbd_sig_hup_handler() > reload_services () > load_interfaces() This might be a bit inconvenient because it is hard to decide when should we manually send a SIGHUP to smbd for refreshing network information.

This patch adds load_interfaces() at fsctl_network_iface_info(), while smbd received FSCTL_QUERY_NETWORK_INTERFACE_INFO would go through this and refresh local_interfaces, then respond to client with up-to-date network information; also refresh num_ifaces to make sure interfaces count is consistent.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=15547

gdb shows that how this patch looks like if smbd received the query and refresh local_interfaces to get up-to-date network information, for example, ubuntu 22.04.3 samba-4.19.3,

1. it was only 2 interfaces, ens3 and ens4
2. a new interface ens5 is introduced and link up.
3. smbd received FSCTL_QUERY_NETWORK_INTERFACE_INFO, refresh local_interfaces
4. now smbd aware 3 interfaces are available: ens3, ens4, and ens5

(gdb) watch local_interfaces
(gdb) commands
bt
ilist local_interfaces
c
end
(gdb) c

<... cut dummy ...>

Hardware watchpoint 1: local_interfaces

Old value = (struct interface *) 0x564ef1838ba0
New value = (struct interface *) 0x564ef180b710
add_interface (ifs=0x564ef1858630) at ../../source3/lib/interface.c:344
344             DEBUG(2,("added interface %s ip=%s ",
#0  add_interface (ifs=0x564ef1858630) at ../../source3/lib/interface.c:344
#1  0x00007ffa33f11913 in load_interfaces () at ../../source3/lib/interface.c:667
#2  0x00007ffa34114129 in fsctl_network_iface_info (mem_ctx=0x564ef18537f0, ev=0x564ef180dda0, xconn=0x564ef1825ec0, in_input=0x564ef1853808, in_max_output=65536, out_output=0x564ef1853820) at ../../source3/smbd/smb2_ioctl_network_fs.c:403
#3  0x00007ffa34114bb1 in smb2_ioctl_network_fs (ctl_code=1311228, ev=0x564ef180dda0, req=0x564ef1853610, state=0x564ef18537f0) at ../../source3/smbd/smb2_ioctl_network_fs.c:661
#4  0x00007ffa3410ff8b in smbd_smb2_ioctl_send (mem_ctx=0x564ef1853230, ev=0x564ef180dda0, smb2req=0x564ef1853230, fsp=0x0, in_ctl_code=1311228, in_input=..., in_max_output=65536, in_flags=1) at ../../source3/smbd/smb2_ioctl.c:465
#5  0x00007ffa3410f33a in smbd_smb2_request_process_ioctl (req=0x564ef1853230) at ../../source3/smbd/smb2_ioctl.c:224
#6  0x00007ffa340f1e3e in smbd_smb2_request_dispatch (req=0x564ef1853230) at ../../source3/smbd/smb2_server.c:3510
#7  0x00007ffa340f6f31 in smbd_smb2_io_handler (xconn=0x564ef1825ec0, fde_flags=1) at ../../source3/smbd/smb2_server.c:5101
#8  0x00007ffa340f7067 in smbd_smb2_connection_handler (ev=0x564ef180dda0, fde=0x564ef18215c0, flags=1, private_data=0x564ef1825ec0) at ../../source3/smbd/smb2_server.c:5139
#9  0x00007ffa33e231b8 in tevent_common_invoke_fd_handler (fde=0x564ef18215c0, flags=1, removed=0x0) at ../../lib/tevent/tevent_fd.c:158
#10 0x00007ffa33e2ee86 in epoll_event_loop (epoll_ev=0x564ef1823c80, tvalp=0x7ffeb20c5270) at ../../lib/tevent/tevent_epoll.c:730
#11 0x00007ffa33e2f619 in epoll_event_loop_once (ev=0x564ef180dda0, location=0x7ffa341e01e8 "../../source3/smbd/smb2_process.c:2017") at ../../lib/tevent/tevent_epoll.c:946
#12 0x00007ffa33e2bb2e in std_event_loop_once (ev=0x564ef180dda0, location=0x7ffa341e01e8 "../../source3/smbd/smb2_process.c:2017") at ../../lib/tevent/tevent_standard.c:110
#13 0x00007ffa33e21b35 in _tevent_loop_once (ev=0x564ef180dda0, location=0x7ffa341e01e8 "../../source3/smbd/smb2_process.c:2017") at ../../lib/tevent/tevent.c:823
#14 0x00007ffa33e21ebd in tevent_common_loop_wait (ev=0x564ef180dda0, location=0x7ffa341e01e8 "../../source3/smbd/smb2_process.c:2017") at ../../lib/tevent/tevent.c:952
#15 0x00007ffa33e2bbd7 in std_event_loop_wait (ev=0x564ef180dda0, location=0x7ffa341e01e8 "../../source3/smbd/smb2_process.c:2017") at ../../lib/tevent/tevent_standard.c:141
#16 0x00007ffa33e21f64 in _tevent_loop_wait (ev=0x564ef180dda0, location=0x7ffa341e01e8 "../../source3/smbd/smb2_process.c:2017") at ../../lib/tevent/tevent.c:971
#17 0x00007ffa340d7a65 in smbd_process (ev_ctx=0x564ef180dda0, msg_ctx=0x564ef17f9110, sock_fd=34, interactive=false) at ../../source3/smbd/smb2_process.c:2017
#18 0x0000564ef088b27c in smbd_accept_connection (ev=0x564ef180dda0, fde=0x564ef1823670, flags=1, private_data=0x564ef1823bf0) at ../../source3/smbd/server.c:1031
#19 0x00007ffa33e231b8 in tevent_common_invoke_fd_handler (fde=0x564ef1823670, flags=1, removed=0x0) at ../../lib/tevent/tevent_fd.c:158
#20 0x00007ffa33e2ee86 in epoll_event_loop (epoll_ev=0x564ef180dfd0, tvalp=0x7ffeb20c5650) at ../../lib/tevent/tevent_epoll.c:730
#21 0x00007ffa33e2f619 in epoll_event_loop_once (ev=0x564ef180dda0, location=0x564ef08907d8 "../../source3/smbd/server.c:1373") at ../../lib/tevent/tevent_epoll.c:946
#22 0x00007ffa33e2bb2e in std_event_loop_once (ev=0x564ef180dda0, location=0x564ef08907d8 "../../source3/smbd/server.c:1373") at ../../lib/tevent/tevent_standard.c:110
#23 0x00007ffa33e21b35 in _tevent_loop_once (ev=0x564ef180dda0, location=0x564ef08907d8 "../../source3/smbd/server.c:1373") at ../../lib/tevent/tevent.c:823
#24 0x00007ffa33e21ebd in tevent_common_loop_wait (ev=0x564ef180dda0, location=0x564ef08907d8 "../../source3/smbd/server.c:1373") at ../../lib/tevent/tevent.c:952
#25 0x00007ffa33e2bbd7 in std_event_loop_wait (ev=0x564ef180dda0, location=0x564ef08907d8 "../../source3/smbd/server.c:1373") at ../../lib/tevent/tevent_standard.c:141
#26 0x00007ffa33e21f64 in _tevent_loop_wait (ev=0x564ef180dda0, location=0x564ef08907d8 "../../source3/smbd/server.c:1373") at ../../lib/tevent/tevent.c:971
#27 0x0000564ef088c02c in smbd_parent_loop (ev_ctx=0x564ef180dda0, parent=0x564ef180bb40) at ../../source3/smbd/server.c:1373
#28 0x0000564ef088e35f in main (argc=1, argv=0x7ffeb20c5c28) at ../../source3/smbd/server.c:2130
name=ens3,      if_index=2, flags=0x11043(IFF_UP=true), speed=1000000000
name=ens5,      if_index=4, flags=0x11043(IFF_UP=true), speed=1000000000
name=ens4,      if_index=3, flags=0x11043(IFF_UP=true), speed=1000000000

ilist is a gdb define macro to help me understand the local_interfaces.

define ilist
  set var $n = $arg0
  while $n
    printf "name=%s,\tif_index=%d, flags=%#x(IFF_UP=%s), speed=%lld\n", $n->name, $n->if_index, $n->flags, $n->flags&IFF_UP ? "true" : "false", $n->linkspeed
    set var $n = $n->next
  end
end

Checklist

• Commits have Signed-off-by: with name/author being identical to the commit author
• (optional) This MR is just one part towards a larger feature.
• (optional, if backport required) Bugzilla bug filed and BUG: tag added
• Test suite updated with functionality tests
• Test suite updated with negative tests
• Documentation updated
• CI timeout is 3h or higher (see Settings/CICD/General pipelines/ Timeout)

Reviewer's checklist:

• There is a test suite reasonably covering new functionality or modifications
• Function naming, parameters, return values, types, etc., are consistent and according to README.Coding.md
• This feature/change has adequate documentation added
• No obvious mistakes in the code