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nuttx/fs/vfs/fs_select.c

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/****************************************************************************
* fs/vfs/fs_select.c
*
* Copyright (C) 2008-2009, 2012-2013 Gregory Nutt. All rights reserved.
* Author: Gregory Nutt <gnutt@nuttx.org>
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
* 3. Neither the name NuttX nor the names of its contributors may be
* used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*
****************************************************************************/
/****************************************************************************
* Included Files
****************************************************************************/
#include <nuttx/config.h>
#include <sys/select.h>
#include <sys/time.h>
#include <string.h>
#include <poll.h>
#include <errno.h>
#include <assert.h>
#include <debug.h>
#include <nuttx/kmalloc.h>
#include <nuttx/cancelpt.h>
#include <nuttx/fs/fs.h>
#include "inode/inode.h"
#ifndef CONFIG_DISABLE_POLL
/****************************************************************************
* Pre-processor Definitions
****************************************************************************/
/****************************************************************************
* Private Functions
****************************************************************************/
/****************************************************************************
* Public Functions
****************************************************************************/
/****************************************************************************
* Name: select
*
* Description:
* select() allows a program to monitor multiple file descriptors, waiting
* until one or more of the file descriptors become "ready" for some class
* of I/O operation (e.g., input possible). A file descriptor is
* considered ready if it is possible to perform the corresponding I/O
* operation (e.g., read(2)) without blocking.
*
* NOTE: poll() is the fundamental API for performing such monitoring
* operation under NuttX. select() is provided for compatibility and
* is simply a layer of added logic on top of poll(). As such, select()
* is more wasteful of resources and poll() is the recommended API to be
* used.
*
* Input parameters:
* nfds - the maximum fd number (+1) of any descriptor in any of the
* three sets.
* readfds - the set of descriptions to monitor for read-ready events
* writefds - the set of descriptions to monitor for write-ready events
* exceptfds - the set of descriptions to monitor for error events
* timeout - Return at this time if none of these events of interest
* occur.
*
* Return:
* 0: Timer expired
* >0: The number of bits set in the three sets of descriptors
* -1: An error occurred (errno will be set appropriately)
*
****************************************************************************/
int select(int nfds, FAR fd_set *readfds, FAR fd_set *writefds,
FAR fd_set *exceptfds, FAR struct timeval *timeout)
{
struct pollfd *pollset;
int errcode = OK;
int fd;
int npfds;
int msec;
int ndx;
int ret;
/* select() is cancellation point */
(void)enter_cancellation_point();
/* How many pollfd structures do we need to allocate? */
/* Initialize the descriptor list for poll() */
for (fd = 0, npfds = 0; fd < nfds; fd++)
{
/* Check if any monitor operation is requested on this fd */
if ((readfds && FD_ISSET(fd, readfds)) ||
(writefds && FD_ISSET(fd, writefds)) ||
(exceptfds && FD_ISSET(fd, exceptfds)))
{
/* Yes.. increment the count of pollfds structures needed */
npfds++;
}
}
/* Allocate the descriptor list for poll() */
pollset = (struct pollfd *)kmm_zalloc(npfds * sizeof(struct pollfd));
if (!pollset)
{
set_errno(ENOMEM);
leave_cancellation_point();
return ERROR;
}
/* Initialize the descriptor list for poll() */
for (fd = 0, ndx = 0; fd < nfds; fd++)
{
int incr = 0;
/* The readfs set holds the set of FDs that the caller can be assured
* of reading from without blocking. Note that POLLHUP is included as
* a read-able condition. POLLHUP will be reported at the end-of-file
* or when a connection is lost. In either case, the read() can then
* be performed without blocking.
*/
if (readfds && FD_ISSET(fd, readfds))
{
pollset[ndx].fd = fd;
pollset[ndx].events |= POLLIN;
incr = 1;
}
/* The writefds set holds the set of FDs that the caller can be assured
* of writing to without blocking.
*/
if (writefds && FD_ISSET(fd, writefds))
{
pollset[ndx].fd = fd;
pollset[ndx].events |= POLLOUT;
incr = 1;
}
/* The exceptfds set holds the set of FDs that are watched for exceptions */
if (exceptfds && FD_ISSET(fd, exceptfds))
{
pollset[ndx].fd = fd;
incr = 1;
}
ndx += incr;
}
DEBUGASSERT(ndx == npfds);
/* Convert the timeout to milliseconds */
if (timeout)
{
/* Calculate the timeout in milliseconds */
msec = timeout->tv_sec * 1000 + timeout->tv_usec / 1000;
}
else
{
/* Any negative value of msec means no timeout */
msec = -1;
}
/* Then let poll do all of the real work. */
ret = poll(pollset, npfds, msec);
if (ret < 0)
{
/* poll() failed! Save the errno value */
errcode = get_errno();
}
/* Now set up the return values */
if (readfds)
{
memset(readfds, 0, sizeof(fd_set));
}
if (writefds)
{
memset(writefds, 0, sizeof(fd_set));
}
if (exceptfds)
{
memset(exceptfds, 0, sizeof(fd_set));
}
/* Convert the poll descriptor list back into selects 3 bitsets */
if (ret > 0)
{
ret = 0;
for (ndx = 0; ndx < npfds; ndx++)
{
/* Check for read conditions. Note that POLLHUP is included as a
* read condition. POLLHUP will be reported when no more data will
* be available (such as when a connection is lost). In either
* case, the read() can then be performed without blocking.
*/
if (readfds)
{
if (pollset[ndx].revents & (POLLIN | POLLHUP))
{
FD_SET(pollset[ndx].fd, readfds);
ret++;
}
}
/* Check for write conditions */
if (writefds)
{
if (pollset[ndx].revents & POLLOUT)
{
FD_SET(pollset[ndx].fd, writefds);
ret++;
}
}
/* Check for exceptions */
if (exceptfds)
{
if (pollset[ndx].revents & POLLERR)
{
FD_SET(pollset[ndx].fd, exceptfds);
ret++;
}
}
}
}
kmm_free(pollset);
/* Did poll() fail above? */
if (ret < 0)
{
/* Yes.. restore the errno value */
set_errno(errcode);
}
leave_cancellation_point();
return ret;
}
#endif /* CONFIG_DISABLE_POLL */
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