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