274 lines
7.4 KiB
C
274 lines
7.4 KiB
C
/****************************************************************************
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* fs/vfs/fs_select.c
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*
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* Licensed to the Apache Software Foundation (ASF) under one or more
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* contributor license agreements. See the NOTICE file distributed with
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* this work for additional information regarding copyright ownership. The
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* ASF licenses this file to you under the Apache License, Version 2.0 (the
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* "License"); you may not use this file except in compliance with the
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* License. You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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* License for the specific language governing permissions and limitations
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* under the License.
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*
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****************************************************************************/
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/****************************************************************************
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* Included Files
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****************************************************************************/
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#include <nuttx/config.h>
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#include <sys/select.h>
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#include <sys/time.h>
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#include <string.h>
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#include <poll.h>
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#include <errno.h>
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#include <assert.h>
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#include <debug.h>
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#include <nuttx/kmalloc.h>
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#include <nuttx/cancelpt.h>
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#include <nuttx/fs/fs.h>
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#include "inode/inode.h"
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/****************************************************************************
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* Public Functions
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****************************************************************************/
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/****************************************************************************
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* Name: select
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*
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* Description:
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* select() allows a program to monitor multiple file descriptors, waiting
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* until one or more of the file descriptors become "ready" for some class
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* of I/O operation (e.g., input possible). A file descriptor is
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* considered ready if it is possible to perform the corresponding I/O
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* operation (e.g., read(2)) without blocking.
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*
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* NOTE: poll() is the fundamental API for performing such monitoring
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* operation under NuttX. select() is provided for compatibility and
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* is simply a layer of added logic on top of poll(). As such, select()
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* is more wasteful of resources and poll() is the recommended API to be
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* used.
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*
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* Input Parameters:
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* nfds - the maximum fd number (+1) of any descriptor in any of the
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* three sets.
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* readfds - the set of descriptions to monitor for read-ready events
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* writefds - the set of descriptions to monitor for write-ready events
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* exceptfds - the set of descriptions to monitor for error events
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* timeout - Return at this time if none of these events of interest
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* occur.
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*
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* Returned Value:
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* 0: Timer expired
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* >0: The number of bits set in the three sets of descriptors
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* -1: An error occurred (errno will be set appropriately)
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*
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****************************************************************************/
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int select(int nfds, FAR fd_set *readfds, FAR fd_set *writefds,
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FAR fd_set *exceptfds, FAR struct timeval *timeout)
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{
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struct pollfd *pollset = NULL;
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int errcode = OK;
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int fd;
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int npfds;
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int msec;
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int ndx;
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int ret;
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/* select() is cancellation point */
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enter_cancellation_point();
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/* How many pollfd structures do we need to allocate? */
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/* Initialize the descriptor list for poll() */
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for (fd = 0, npfds = 0; fd < nfds; fd++)
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{
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/* Check if any monitor operation is requested on this fd */
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if ((readfds && FD_ISSET(fd, readfds)) ||
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(writefds && FD_ISSET(fd, writefds)) ||
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(exceptfds && FD_ISSET(fd, exceptfds)))
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{
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/* Yes.. increment the count of pollfds structures needed */
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npfds++;
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}
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}
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/* Allocate the descriptor list for poll() */
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if (npfds > 0)
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{
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pollset = (FAR struct pollfd *)
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kmm_zalloc(npfds * sizeof(struct pollfd));
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if (pollset == NULL)
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{
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errcode = ENOMEM;
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goto errout;
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}
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}
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/* Initialize the descriptor list for poll() */
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for (fd = 0, ndx = 0; fd < nfds; fd++)
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{
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int incr = 0;
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/* The readfs set holds the set of FDs that the caller can be assured
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* of reading from without blocking. Note that POLLHUP is included as
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* a read-able condition. POLLHUP will be reported at the end-of-file
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* or when a connection is lost. In either case, the read() can then
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* be performed without blocking.
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*/
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if (readfds && FD_ISSET(fd, readfds))
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{
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pollset[ndx].fd = fd;
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pollset[ndx].events |= POLLIN;
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incr = 1;
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}
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/* The writefds set holds the set of FDs that the caller can be assured
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* of writing to without blocking.
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*/
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if (writefds && FD_ISSET(fd, writefds))
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{
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pollset[ndx].fd = fd;
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pollset[ndx].events |= POLLOUT;
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incr = 1;
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}
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/* The exceptfds set holds the set of FDs that are watched for
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* exceptions
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*/
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if (exceptfds && FD_ISSET(fd, exceptfds))
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{
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pollset[ndx].fd = fd;
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incr = 1;
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}
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ndx += incr;
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}
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DEBUGASSERT(ndx == npfds);
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/* Convert the timeout to milliseconds */
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if (timeout)
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{
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/* Calculate the timeout in milliseconds */
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msec = timeout->tv_sec * 1000 + timeout->tv_usec / 1000;
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}
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else
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{
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/* Any negative value of msec means no timeout */
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msec = -1;
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}
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/* Then let poll do all of the real work. */
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ret = nx_poll(pollset, npfds, msec);
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if (ret < 0)
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{
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/* poll() failed! Save the errno value */
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errcode = -ret;
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}
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/* Now set up the return values */
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if (readfds)
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{
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memset(readfds, 0, sizeof(fd_set));
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}
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if (writefds)
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{
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memset(writefds, 0, sizeof(fd_set));
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}
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if (exceptfds)
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{
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memset(exceptfds, 0, sizeof(fd_set));
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}
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/* Convert the poll descriptor list back into selects 3 bitsets */
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if (ret > 0)
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{
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ret = 0;
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for (ndx = 0; ndx < npfds; ndx++)
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{
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/* Check for read conditions. Note that POLLHUP is included as a
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* read condition. POLLHUP will be reported when no more data will
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* be available (such as when a connection is lost). In either
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* case, the read() can then be performed without blocking.
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*/
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if (readfds)
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{
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if (pollset[ndx].revents & (POLLIN | POLLHUP))
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{
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FD_SET(pollset[ndx].fd, readfds);
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ret++;
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}
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}
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/* Check for write conditions */
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if (writefds)
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{
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if (pollset[ndx].revents & POLLOUT)
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{
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FD_SET(pollset[ndx].fd, writefds);
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ret++;
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}
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}
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/* Check for exceptions */
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if (exceptfds)
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{
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if (pollset[ndx].revents & POLLERR)
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{
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FD_SET(pollset[ndx].fd, exceptfds);
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ret++;
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}
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}
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}
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}
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kmm_free(pollset);
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/* Did poll() fail above? */
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if (ret >= 0)
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{
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leave_cancellation_point();
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return ret;
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}
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errout:
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set_errno(errcode);
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leave_cancellation_point();
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return ERROR;
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}
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