Commit Graph

20 Commits

Author SHA1 Message Date
Denys Vlasenko
3293bc1469 udhcpd: fix "not dying on SIGTERM"
Fixes:
	commit 52a515d187
	"udhcp: use poll() instead of select()"
	Feb 16 2017

udhcp_sp_read() is meant to check whether signal pipe indeed has some data to read.
In the above commit, it was changed as follows:

-	if (!FD_ISSET(signal_pipe.rd, rfds))
+	if (!pfds[0].revents)
		return 0;

The problem is, the check was working for select() purely by accident.
Caught signal interrupts select()/poll() syscalls, they return with EINTR
(regardless of SA_RESTART flag in sigaction). _Then_ signal handler is invoked.
IOW: they can't see any changes to fd state caused by signal haldler
(in our case, signal handler makes signal pipe ready to be read).

For select(), it means that rfds[] bit array is unmodified, bit of signal
pipe's read fd is still set, and the above check "works": it thinks select()
says there is data to read.

This accident does not work for poll(): .revents stays clear, and we do not
try reading signal pipe as we should. In udhcpd, we fall through and block
in socket read. Further SIGTERM signals simply cause socket read to be
interrupted and then restarted (since SIGTERM handler has SA_RESTART=1).

Fixing this as follows: remove the check altogether. Set signal pipe read fd
to nonblocking mode. Always read it in udhcp_sp_read().
If read fails, assume it's EAGAIN and return 0 ("no signal seen").

udhcpd avoids reading signal pipe on every recvd packet by looping if EINTR
(using safe_poll()) - thus ensuring we have correct .revents for all fds -
and calling udhcp_sp_read() only if pfds[0].revents!=0.

udhcpc performs much fewer reads (typically it sleeps >99.999% of the time),
there is no need to optimize it: can call udhcp_sp_read() after each poll
unconditionally.

To robustify socket reads, unconditionally set pfds[1].revents=0
in udhcp_sp_fd_set() (which is before poll), and check it before reading
network socket in udhcpd.

TODO:
This might still fail: if pfds[1].revents=POLLIN, socket read may still block.
There are rare cases when select/poll indicates that data can be read,
but then actual read still blocks (one such case is UDP packets with
wrong checksum). General advise is, if you use a poll/select loop,
keep all your fds nonblocking.
Maybe we should also do that to our network sockets?

function                                             old     new   delta
udhcp_sp_setup                                        55      65     +10
udhcp_sp_fd_set                                       54      60      +6
udhcp_sp_read                                         46      36     -10
udhcpd_main                                         1451    1437     -14
udhcpc_main                                         2723    2708     -15
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 2/3 up/down: 16/-39)            Total: -23 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
2018-03-10 19:34:39 +01:00
Denys Vlasenko
52a515d187 udhcp: use poll() instead of select()
function                                             old     new   delta
udhcp_sp_read                                         65      46     -19
udhcp_sp_fd_set                                       79      54     -25
udhcpd_main                                         1530    1482     -48
udhcpc_main                                         2780    2730     -50
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 0/4 up/down: 0/-142)           Total: -142 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
2017-02-16 23:25:44 +01:00
Denys Vlasenko
dc207f6696 udhcp: do not clobber errno by signal handler
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
2017-02-16 20:04:19 +01:00
Denys Vlasenko
385b4562e3 udhcp: cosmetic cleanups; one case of s/full_read/xread/
function                                             old     new   delta
dumpleases_main                                      632     623      -9

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
2010-03-26 10:09:34 +01:00
Denys Vlasenko
6331cf059c *: use "can't" instead of "cannot"
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
2009-11-13 09:08:27 +01:00
Denis Vlasenko
f1980f67d3 dhcp: add FAST_FUNC as appropriate. -160 bytes. 2008-09-26 09:34:59 +00:00
Denis Vlasenko
25591c322c libbb: introduce bb_signals and bb_signals_recursive,
which sets same handler for many signals. sig_catch is nuked
(bb_signals_recursive is more descriptive name).
*: use them as appropriate. 

function                                             old     new   delta
bb_signals_recursive                                   -      95     +95
bb_signals                                             -      52     +52
run_command                                          258     273     +15
svlogd_main                                         1368    1377      +9
runsv_main                                          1746    1752      +6
runsvdir_main                                       1643    1646      +3
UNSPEC_print                                          64      66      +2
time_main                                           1128    1127      -1
...
resize_main                                          246     210     -36
sig_catch                                             63       -     -63
set_fatal_sighandler                                  85      14     -71
------------------------------------------------------------------------------
(add/remove: 2/1 grow/shrink: 5/24 up/down: 182/-548)        Total: -366 bytes
2008-02-16 22:58:56 +00:00
Denis Vlasenko
3718832a15 *: more readable handling of pipe fds. No code changes. 2008-02-16 13:20:56 +00:00
Denis Vlasenko
223bc97f61 udhcpc: an option to perform ARP check (Jonas Danielsson <jonas.danielsson@axis.com>)
configurable, ~+300 bytes when on.
2007-11-22 00:58:49 +00:00
Denis Vlasenko
96e1b38586 introduce and use close_on_exec_on(fd). -50 bytes. 2007-09-30 23:50:48 +00:00
Denis Vlasenko
5a6aeddfa7 xpipe: introduce (saves ~170 bytes)
udhcp/signalpipe.c: use pipe instead of socketpair.
2007-05-26 16:44:20 +00:00
Denis Vlasenko
0fe67b16ce udhcp: socketpair can fail if AF_UNIX is not available (e.g. if module is not loaded).
Error out on that.
2007-05-24 12:19:56 +00:00
Denis Vlasenko
5a3395bc01 udhcp: fix indentation and style.
Eliminate (group) a lot of smallish *.h files
Remove lots of unneeded #includes
2006-11-18 19:51:32 +00:00
Denis Vlasenko
ea62077b85 add open_read_close() and similar stuff 2006-10-14 02:23:43 +00:00
Denis Vlasenko
3538b9a882 Implement optional syslog logging using ordinary
bb_xx_msg calls, and convert networking/* to it.
The rest of bbox will be converted gradually.
2006-09-06 18:36:50 +00:00
"Robert P. J. Day"
63fc1a9e08 Standardize on the vi editing directives being on the first line. 2006-07-02 19:47:05 +00:00
Mike Frysinger
7031f62d9b add back in udhcp support 2006-05-08 03:20:50 +00:00
Mike Frysinger
787140df39 remove in place of external link 2006-03-23 23:44:29 +00:00
Eric Andersen
aff114c33d Larry Doolittle writes:
This is a bulk spelling fix patch against busybox-1.00-pre10.
If anyone gets a corrupted copy (and cares), let me know and
I will make alternate arrangements.

Erik - please apply.

Authors - please check that I didn't corrupt any meaning.

Package importers - see if any of these changes should be
passed to the upstream authors.

I glossed over lots of sloppy capitalizations, missing apostrophes,
mixed American/British spellings, and German-style compound words.

What is "pretect redefined for test" in cmdedit.c?

Good luck on the 1.00 release!

      - Larry
2004-04-14 17:51:38 +00:00
Russ Dill
4e864a36b6 Finish remerging busybox udhcp and udhcp. Some cleanups as well. 2003-12-18 22:25:38 +00:00