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Fixes:
commit 52a515d18724bbb34e3ccbbb0218efcc4eccc0a8
"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>
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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>
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Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
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function old new delta
dumpleases_main 632 623 -9
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
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Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
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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
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<jonas.danielsson@axis.com>)
configurable, ~+300 bytes when on.
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udhcp/signalpipe.c: use pipe instead of socketpair.
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not loaded).
Error out on that.
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Eliminate (group) a lot of smallish *.h files
Remove lots of unneeded #includes
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bb_xx_msg calls, and convert networking/* to it.
The rest of bbox will be converted gradually.
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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
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