277 lines
11 KiB
C
277 lines
11 KiB
C
/****************************************************************************
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* libc/aio/aio_read.c
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*
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* Copyright (C) 2014 Gregory Nutt. All rights reserved.
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* Author: Gregory Nutt <gnutt@nuttx.org>
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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*
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in
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* the documentation and/or other materials provided with the
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* distribution.
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* 3. Neither the name NuttX nor the names of its contributors may be
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* used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
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* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
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* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
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* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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* POSSIBILITY OF SUCH DAMAGE.
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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 <unistd.h>
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#include <sched.h>
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#include <aio.h>
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#include <assert.h>
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#include <errno.h>
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#include <debug.h>
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#include <nuttx/wqueue.h>
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#include "aio/aio.h"
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#ifdef CONFIG_FS_AIO
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/****************************************************************************
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* Pre-processor Definitions
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****************************************************************************/
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/* Configuration ************************************************************/
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/****************************************************************************
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* Private Types
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****************************************************************************/
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/****************************************************************************
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* Private Variables
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****************************************************************************/
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/****************************************************************************
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* Public Variables
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****************************************************************************/
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/****************************************************************************
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* Private Functions
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****************************************************************************/
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/****************************************************************************
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* Name: aio_read_worker
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*
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* Description:
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* This function executes on the worker thread and performs the
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* asynchronous I/O operation.
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*
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* Input Parameters:
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* arg - Worker argument. In this case, a pointer to an instance of
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* struct aiocb cast to void *.
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*
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* Returned Value:
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* None
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*
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****************************************************************************/
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static void aio_read_worker(FAR void *arg)
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{
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FAR struct aiocb *aiocbp = (FAR struct aiocb *)arg;
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DEBUGASSERT(arg);
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ssize_t nread;
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/* Perform the read using:
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*
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* aio_fildes - File descriptor
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* aio_buf - Location of buffer
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* aio_nbytes - Length of transfer
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* aio_offset - File offset
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*/
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nread = pread(aiocbp->aio_fildes, (FAR void *)aiocbp->aio_buf,
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aiocbp->aio_nbytes, aiocbp->aio_offset);
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/* Set the result of the read */
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if (nread < 0)
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{
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int errcode = get_errno();
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fdbg("ERROR: pread failed: %d\n", errode);
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DEBUGASSERT(errcode > 0);
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aiocbp->aio_result = -errcode;
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}
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else
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{
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aiocbp->aio_result = nread;
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}
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/* Signal the client */
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(void)aio_signal(aiocbp);
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}
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/****************************************************************************
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* Public Functions
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****************************************************************************/
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/****************************************************************************
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* Name: aio_read
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*
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* Description:
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* The aio_read() function reads aiocbp->aio_nbytes from the file
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* associated with aiocbp->aio_fildes into the buffer pointed to by
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* aiocbp->aio_buf. The function call will return when the read request
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* has been initiated or queued to the file or device (even when the data
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* cannot be delivered immediately).
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*
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* The aiocbp value may be used as an argument to aio_error() and
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* aio_return() in order to determine the error status and return status,
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* respectively, of the asynchronous operation while it is proceeding. If
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* an error condition is encountered during queuing, the function call
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* will return without having initiated or queued the request. The
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* requested operation takes place at the absolute position in the file as
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* given by aio_offset, as if lseek() were called immediately prior to the
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* operation with an offset equal to aio_offset and a whence equal to
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* SEEK_SET. After a successful call to enqueue an asynchronous I/O
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* operation, the value of the file offset for the file is unspecified.
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*
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* The aiocbp->aio_lio_opcode field will be ignored by aio_read().
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*
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* The aiocbp argument points to an aiocb structure. If the buffer pointed
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* to by aiocbp->aio_buf or the control block pointed to by aiocbp becomes
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* an illegal address prior to asynchronous I/O completion, then the
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* behavior is undefined.
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*
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* Simultaneous asynchronous operations using the same aiocbp produce
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* undefined results.
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*
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* For any system action that changes the process memory space while an
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* synchronous I/O is outstanding to the address range being changed, the
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* result of that action is undefined.
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*
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* Input Parameters:
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* aiocbp - A pointer to an instance of struct aiocb
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*
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* Returned Value:
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*
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* The aio_read() function will return the value zero if the I/O operation
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* is successfully queued; otherwise, the function will return the value
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* -1 and set errno to indicate the error. The aio_read() function will
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* ail if:
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*
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* EAGAIN - The requested asynchronous I/O operation was not queued due to
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* system resource limitations.
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*
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* Each of the following conditions may be detected synchronously at the
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* time of the call to aio_read(), or asynchronously. If any of the
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* conditions below are detected synchronously, the aio_read() function
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* will return -1 and set errno to the corresponding value. If any of the
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* conditions below are detected asynchronously, the return status of the
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* asynchronous operation is set to -1, and the error status of the
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* asynchronous operation is set to the corresponding value.
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*
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* EBADF - The aiocbp->aio_fildes argument is not a valid file descriptor
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* open for reading.
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* EINVAL - The file offset value implied by aiocbp->aio_offset would be
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* invalid, aiocbp->aio_reqprio is not a valid value, or
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* aiocbp->aio_nbytes is an invalid value.
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*
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* In the case that the aio_read() successfully queues the I/O operation
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* but the operation is subsequently cancelled or encounters an error, the
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* return status of the asynchronous operation is one of the values
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* normally returned by the read() function call. In addition, the error
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* status of the asynchronous operation is set to one of the error
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* statuses normally set by the read() function call, or one of the
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* following values:
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*
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* EBADF - The aiocbp->aio_fildes argument is not a valid file descriptor
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* open for reading.
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* ECANCELED - The requested I/O was cancelled before the I/O completed
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* due to an explicit aio_cancel() request.
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* EINVAL - The file offset value implied by aiocbp->aio_offset would be
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* invalid.
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*
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* The following condition may be detected synchronously or asynchronously:
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*
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* EOVERFLOW - The file is a regular file, aiobcp->aio_nbytes is greater
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* than 0, and the starting offset in aiobcp->aio_offset is before the
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* end-of-file and is at or beyond the offset maximum in the open file
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* description associated with aiocbp->aio_fildes.
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*
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* POSIX Compliance:
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* - The POSIX specification of asynchronous I/O implies that a thread is
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* created for each I/O operation. The standard requires that if
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* prioritized I/O is supported for this file, then the asynchronous
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* operation will be submitted at a priority equal to a base scheduling
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* priority minus aiocbp->aio_reqprio. If Thread Execution Scheduling is
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* not supported, then the base scheduling priority is that of the calling
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* thread.
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*
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* My initial gut feeling is the creating a new thread on each asynchronous
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* I/O operation would not be a good use of resources in a deeply embedded
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* system. So I decided to execute all asynchronous I/O on a low-priority
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* or user-space worker thread. There are two negative consequences of this
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* decision that need to be revisited:
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*
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* 1) The worker thread runs at a fixed priority making it impossible to
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* meet the POSIX requirement for asynchronous I/O. That standard
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* specifically requires varying priority.
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* 2) On the worker thread, each I/O will still be performed synchronously,
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* one at a time. This is not a violation of the POSIX requirement,
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* but one would think there could be opportunities for concurrent I/O.
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*
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* In reality, in a small embedded system, there will probably only be one
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* real file system and, in this case, the I/O will be performed sequentially
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* anyway. Most simple embedded hardware will not support any concurrent
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* accesses.
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*
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* - Most errors required in the standard are not detected at this point.
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* There are no pre-queuing checks for the validity of the operation.
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*
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****************************************************************************/
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int aio_read(FAR struct aiocb *aiocbp)
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{
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int ret;
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DEBUGASSERT(aiocbp);
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/* The result -EINPROGRESS means that the transfer has not yet completed */
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aiocbp->aio_result = -EINPROGRESS;
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aiocbp->aio_priv = NULL;
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/* Save the ID of the calling, client thread */
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aiocbp->aio_pid = getpid();
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/* Defer the work to the worker thread */
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ret = work_queue(LPWORK, &aiocbp->aio_work, aio_read_worker, aiocbp, 0);
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if (ret < 0)
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{
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aiocbp->aio_result = ret;
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set_errno(ret);
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return ERROR;
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}
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return OK;
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}
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#endif /* CONFIG_FS_AIO */
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