samba: share select wrappers.

Guenther

1 files changed, 210 insertions, 0 deletions

diff --git a/lib/util/select.c b/lib/util/select.c
new file mode 100644
index 0000000000..61df649526
--- /dev/null
+++ b/lib/util/select.c
@@ -0,0 +1,210 @@
+/*
+   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 3 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, see <http://www.gnu.org/licenses/>.
+*/
+
+#include "includes.h"
+#include "system/filesys.h"
+#include "system/select.h"
+#include "lib/util/select.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(char c)
+{
+	int saved_errno = errno;
+
+	if (!initialised) return;
+
+	if (pipe_written > pipe_read+256) return;
+
+	if (write(select_pipe[1], &c, 1) == 1) pipe_written++;
+
+	errno = saved_errno;
+}
+
+/*******************************************************************
+ Like select() but avoids the signal race using a pipe
+ it also guuarantees 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 != sys_getpid()) {
+		if (pipe(select_pipe) == -1)
+		{
+			DEBUG(0, ("sys_select: pipe failed (%s)\n",
+				strerror(errno)));
+			if (readfds != NULL)
+				FD_ZERO(readfds);
+			if (writefds != NULL)
+				FD_ZERO(writefds);
+			if (errorfds != NULL)
+				FD_ZERO(errorfds);
+			return -1;
+		}
+
+		/*
+		 * 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");
+		if(set_blocking(select_pipe[1],0)==-1)
+			smb_panic("select_pipe[1]: O_NONBLOCK failed");
+
+		initialised = sys_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;
+#if 0
+			/* JRA - we can use this to debug the signal messaging... */
+			DEBUG(0,("select got %u signal\n", (unsigned int)c));
+#endif
+			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;
+	struct timespec end_time;
+
+	readfds2 = (readfds ? &readfds_buf : NULL);
+	writefds2 = (writefds ? &writefds_buf : NULL);
+	errorfds2 = (errorfds ? &errorfds_buf : NULL);
+	if (tval) {
+		clock_gettime_mono(&end_time);
+		end_time.tv_sec += tval->tv_sec;
+		end_time.tv_nsec += tval->tv_usec *1000;
+		end_time.tv_sec += end_time.tv_nsec / 1000000000;
+		end_time.tv_nsec %= 1000000000;
+		errno = 0;
+		tval2 = *tval;
+		ptval = &tval2;
+	} else {
+		ptval = NULL;
+	}
+
+	do {
+		if (readfds)
+			readfds_buf = *readfds;
+		if (writefds)
+			writefds_buf = *writefds;
+		if (errorfds)
+			errorfds_buf = *errorfds;
+		if (ptval && (errno == EINTR)) {
+			struct timespec now_time;
+			int64_t tdif;
+
+			clock_gettime_mono(&now_time);
+			tdif = nsec_time_diff(&end_time,&now_time);
+			if (tdif <= 0) {
+				ret = 0; /* time expired. */
+				break;
+			}
+			ptval->tv_sec = tdif / 1000000000;
+			ptval->tv_usec = (tdif % 1000000000) / 1000;
+		}
+
+		/* 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;
+}