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https://github.com/samba-team/samba.git
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cd1ad031a6
(This used to be commit 85d3ffb270
)
130 lines
3.7 KiB
C
130 lines
3.7 KiB
C
/*
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Unix SMB/Netbios implementation.
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Version 3.0
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Samba select/poll implementation
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Copyright (C) Andrew Tridgell 1992-1998
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program; if not, write to the Free Software
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Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
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*/
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#include "includes.h"
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/* this is here because it allows us to avoid a nasty race in signal handling.
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We need to guarantee that when we get a signal we get out of a select immediately
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but doing that involves a race condition. We can avoid the race by getting the
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signal handler to write to a pipe that is in the select/poll list
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this means all Samba signal handlers should call sys_select_signal()
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*/
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static pid_t initialised;
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static int select_pipe[2];
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static VOLATILE unsigned pipe_written, pipe_read;
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/*******************************************************************
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call this from all Samba signal handlers if you want to avoid a
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nasty signal race condition
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********************************************************************/
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void sys_select_signal(void)
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{
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char c = 1;
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if (!initialised) return;
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if (pipe_written > pipe_read+256) return;
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if (write(select_pipe[1], &c, 1) == 1) pipe_written++;
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}
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/*******************************************************************
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like select() but avoids the signal race using a pipe
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it also guarantees that fds on return only ever contains bits set
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for file descriptors that were readable
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********************************************************************/
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int sys_select(int maxfd, fd_set *fds,struct timeval *tval)
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{
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int ret, saved_errno;
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if (initialised != sys_getpid()) {
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pipe(select_pipe);
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/*
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* These next two lines seem to fix a bug with the Linux
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* 2.0.x kernel (and probably other UNIXes as well) where
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* the one byte read below can block even though the
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* select returned that there is data in the pipe and
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* the pipe_written variable was incremented. Thanks to
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* HP for finding this one. JRA.
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*/
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if(set_blocking(select_pipe[0],0)==-1)
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smb_panic("select_pipe[0]: O_NONBLOCK failed.\n");
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if(set_blocking(select_pipe[1],0)==-1)
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smb_panic("select_pipe[1]: O_NONBLOCK failed.\n");
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initialised = sys_getpid();
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}
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maxfd = MAX(select_pipe[0]+1, maxfd);
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FD_SET(select_pipe[0], fds);
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errno = 0;
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ret = select(maxfd,fds,NULL,NULL,tval);
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if (ret <= 0) {
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FD_ZERO(fds);
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}
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if (FD_ISSET(select_pipe[0], fds)) {
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FD_CLR(select_pipe[0], fds);
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ret--;
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if (ret == 0) {
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ret = -1;
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errno = EINTR;
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}
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}
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saved_errno = errno;
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while (pipe_written != pipe_read) {
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char c;
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/* Due to the linux kernel bug in 2.0.x, we
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* always increment here even if the read failed... */
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read(select_pipe[0], &c, 1);
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pipe_read++;
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}
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errno = saved_errno;
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return ret;
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}
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/*******************************************************************
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similar to sys_select() but catch EINTR and continue
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this is what sys_select() used to do in Samba
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********************************************************************/
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int sys_select_intr(int maxfd, fd_set *fds,struct timeval *tval)
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{
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int ret;
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fd_set fds2;
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do {
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fds2 = *fds;
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ret = sys_select(maxfd, &fds2, tval);
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} while (ret == -1 && errno == EINTR);
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*fds = fds2;
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return ret;
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}
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