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Diffstat (limited to 'source4/lib/util/select.c')
| -rw-r--r-- | source4/lib/util/select.c | 169 |
1 files changed, 169 insertions, 0 deletions
diff --git a/source4/lib/util/select.c b/source4/lib/util/select.c new file mode 100644 index 0000000000..a1b2e04065 --- /dev/null +++ b/source4/lib/util/select.c @@ -0,0 +1,169 @@ +/* + 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" +#include "system/filesys.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 *readfds, fd_set *writefds, fd_set *errorfds, struct timeval *tval) +{ + int ret, saved_errno; + fd_set *readfds2, readfds_buf; + + if (initialised != 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 = getpid(); + } + + maxfd = MAX(select_pipe[0]+1, maxfd); + + /* If readfds is NULL we need to provide our own set. */ + if (readfds) { + readfds2 = readfds; + } else { + readfds2 = &readfds_buf; + FD_ZERO(readfds2); + } + FD_SET(select_pipe[0], readfds2); + + errno = 0; + ret = select(maxfd,readfds2,writefds,errorfds,tval); + + if (ret <= 0) { + FD_ZERO(readfds2); + if (writefds) + FD_ZERO(writefds); + if (errorfds) + FD_ZERO(errorfds); + } else if (FD_ISSET(select_pipe[0], readfds2)) { + char c; + saved_errno = errno; + if (read(select_pipe[0], &c, 1) == 1) { + pipe_read++; + /* Mark Weaver <mark-clist@npsl.co.uk> pointed out a critical + fix to ensure we don't lose signals. We must always + return -1 when the select pipe is set, otherwise if another + fd is also ready (so ret == 2) then we used to eat the + byte in the pipe and lose the signal. JRA. + */ + ret = -1; + errno = EINTR; + } else { + FD_CLR(select_pipe[0], readfds2); + ret--; + 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 *readfds, fd_set *writefds, fd_set *errorfds, struct timeval *tval) +{ + int ret; + fd_set *readfds2, readfds_buf, *writefds2, writefds_buf, *errorfds2, errorfds_buf; + struct timeval tval2, *ptval; + + readfds2 = (readfds ? &readfds_buf : NULL); + writefds2 = (writefds ? &writefds_buf : NULL); + errorfds2 = (errorfds ? &errorfds_buf : NULL); + ptval = (tval ? &tval2 : NULL); + + do { + if (readfds) + readfds_buf = *readfds; + if (writefds) + writefds_buf = *writefds; + if (errorfds) + errorfds_buf = *errorfds; + if (tval) + tval2 = *tval; + + /* We must use select and not sys_select here. If we use + sys_select we'd lose the fact a signal occurred when sys_select + read a byte from the pipe. Fix from Mark Weaver + <mark-clist@npsl.co.uk> + */ + + ret = select(maxfd, readfds2, writefds2, errorfds2, ptval); + } while (ret == -1 && errno == EINTR); + + if (readfds) + *readfds = readfds_buf; + if (writefds) + *writefds = writefds_buf; + if (errorfds) + *errorfds = errorfds_buf; + + return ret; +} |