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/* Work around the bug in Solaris 7 whereby a fd that is opened on
/dev/null will cause select/poll to hang when given a NULL timeout.
Copyright (C) 2004 Free Software Foundation, Inc.
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, 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., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. */
/* written by Mark D. Baushke */
/*
* Observed on Solaris 7:
* If /dev/null is in the readfds set, it will never be marked as
* ready by the OS. In the case of a /dev/null fd being the only fd
* in the select set and timeout == NULL, the select will hang.
* If /dev/null is in the exceptfds set, it will not be set on
* return from select().
*/
#ifdef HAVE_CONFIG_H
# include <config.h>
#endif /* HAVE_CONFIG_H */
/* The rpl_select function calls the real select. */
#undef select
#include <stdbool.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <errno.h>
#ifdef HAVE_UNISTD_H
# include <unistd.h>
#endif /* HAVE_UNISTD_H */
#include "minmax.h"
#include "xtime.h"
static struct stat devnull;
static int devnull_set = -1;
int
rpl_select (int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds,
struct timeval *timeout)
{
int ret = 0;
/* Argument checking */
if (nfds < 1 || nfds > FD_SETSIZE)
{
errno = EINVAL;
return -1;
}
/* Perform the initial stat on /dev/null */
if (devnull_set == -1)
devnull_set = stat ("/dev/null", &devnull);
if (devnull_set >= 0)
{
int fd;
int maxfd = -1;
fd_set null_rfds, null_wfds;
bool altered = false; /* Whether we have altered the caller's args.
*/
FD_ZERO (&null_rfds);
FD_ZERO (&null_wfds);
for (fd = 0; fd < nfds; fd++)
{
/* Check the callers bits for interesting fds */
bool isread = (readfds && FD_ISSET (fd, readfds));
bool isexcept = (exceptfds && FD_ISSET (fd, exceptfds));
bool iswrite = (writefds && FD_ISSET (fd, writefds));
/* Check interesting fds against /dev/null */
if (isread || iswrite || isexcept)
{
struct stat sb;
/* Equivalent to /dev/null ? */
if (fstat (fd, &sb) >= 0
&& sb.st_dev == devnull.st_dev
&& sb.st_ino == devnull.st_ino
&& sb.st_mode == devnull.st_mode
&& sb.st_uid == devnull.st_uid
&& sb.st_gid == devnull.st_gid
&& sb.st_size == devnull.st_size
&& sb.st_blocks == devnull.st_blocks
&& sb.st_blksize == devnull.st_blksize)
{
/* Save the interesting bits for later use. */
if (isread)
{
FD_SET (fd, &null_rfds);
FD_CLR (fd, readfds);
altered = true;
}
if (isexcept)
/* Pass exception bits through.
*
* At the moment, we only know that this bug
* exists in Solaris 7 and so this file should
* only be compiled on Solaris 7. Since Solaris 7
* never returns ready for exceptions on
* /dev/null, we probably could assume this too,
* but since Solaris 9 is known to always return
* ready for exceptions on /dev/null, pass this
* through in case any other systems turn out to
* do the same. Besides, this will cause the
* timeout to be processed as it would have been
* otherwise.
*/
maxfd = MAX (maxfd, fd);
if (iswrite)
{
/* We know of no bugs involving selecting /dev/null
* writefds, but we also know that /dev/null is always
* ready for write. Therefore, since we have already
* performed all the necessary processing, avoid calling
* the system select for this case.
*/
FD_SET (fd, &null_wfds);
FD_CLR (fd, writefds);
altered = true;
}
}
else
/* A non-/dev/null fd is present. */
maxfd = MAX (maxfd, fd);
}
}
if (maxfd >= 0)
{
/* we need to call select, one way or another. */
if (altered)
{
/* We already have some ready bits set, so timeout immediately
* if no bits are set.
*/
struct timeval ztime;
ztime.tv_sec = 0;
ztime.tv_usec = 0;
ret = select (maxfd + 1, readfds, writefds, exceptfds, &ztime);
if (ret == 0)
{
/* Timeout. Zero the sets since the system select might
* not have.
*/
if (readfds)
FD_ZERO (readfds);
if (exceptfds)
FD_ZERO (exceptfds);
if (writefds)
FD_ZERO (writefds);
}
}
else
/* No /dev/null fds. Call select just as the user specified. */
ret = select (maxfd + 1, readfds, writefds, exceptfds, timeout);
}
/*
* Borrowed from the Solaris 7 man page for select(3c):
*
* On successful completion, the objects pointed to by the
* readfds, writefds, and exceptfds arguments are modified to
* indicate which file descriptors are ready for reading,
* ready for writing, or have an error condition pending,
* respectively. For each file descriptor less than nfds, the
* corresponding bit will be set on successful completion if
* it was set on input and the associated condition is true
* for that file descriptor.
*
* On failure, the objects pointed to by the readfds,
* writefds, and exceptfds arguments are not modified. If the
* timeout interval expires without the specified condition
* being true for any of the specified file descriptors, the
* objects pointed to by the readfs, writefs, and errorfds
* arguments have all bits set to 0.
*
* On successful completion, select() returns the total number
* of bits set in the bit masks. Otherwise, -1 is returned,
* and errno is set to indicate the error.
*/
/* Fix up the fd sets for any changes we may have made. */
if (altered)
{
/* Tell the caller that nothing is blocking the /dev/null fds */
for (fd = 0; fd < nfds; fd++)
{
/* If ret < 0, then we still need to restore the fd sets. */
if (FD_ISSET (fd, &null_rfds))
{
FD_SET (fd, readfds);
if (ret >= 0)
ret++;
}
if (FD_ISSET (fd, &null_wfds))
{
FD_SET (fd, writefds);
if (ret >= 0)
ret++;
}
}
}
}
else
ret = select (nfds, readfds, writefds, exceptfds, timeout);
return ret;
}
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