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Add pread() and pwrite()

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This commit is contained in:
Gregory Nutt 2014-10-04 07:31:13 -06:00
parent 4764c95670
commit 948be542a1
5 changed files with 269 additions and 3 deletions
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8
fs/vfs/Make.defs
View File

@ -43,6 +43,10 @@ ifneq ($(CONFIG_NSOCKET_DESCRIPTORS),0)
CSRCS += fs_close.c fs_read.c fs_write.c fs_ioctl.c fs_poll.c fs_select.c
# Support for positional file access
CSRCS += fs_pread.c fs_pwrite.c
# Support for network access using streams
ifneq ($(CONFIG_NFILE_STREAMS),0)
@ -70,6 +74,10 @@ CSRCS += fs_fsync.c fs_ioctl.c fs_lseek.c fs_mkdir.c fs_open.c fs_poll.c
CSRCS += fs_read.c fs_rename.c fs_rmdir.c fs_stat.c fs_statfs.c fs_select.c
CSRCS += fs_unlink.c fs_write.c
# Support for positional file access
CSRCS += fs_pread.c fs_pwrite.c
# Stream support
ifneq ($(CONFIG_NFILE_STREAMS),0)

129
fs/vfs/fs_pread.c Normal file
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@ -0,0 +1,129 @@
/****************************************************************************
* fs/vfs/fs_pread.c
*
* Copyright (C) 2014 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/types.h>
#include <unistd.h>
#include <errno.h>
/****************************************************************************
* Private Functions
****************************************************************************/
/****************************************************************************
* Public Functions
****************************************************************************/
/****************************************************************************
* Name: pread
*
* Description:
* The pread() function performs the same action as read(), except that it
* reads from a given position in the file without changing the file
* pointer. The first three arguments to pread() are the same as read()
* with the addition of a fourth argument offset for the desired position
* inside the file. An attempt to perform a pread() on a file that is
* incapable of seeking results in an error.
*
* NOTE: This function could have been wholly implemented within libc but
* it is not. Why? Because if pread were implemented in libc, it would
* require four system calls. If it is implemented within the kernel,
* only three.
*
* Parameters:
* file File structure instance
* buf User-provided to save the data
* nbytes The maximum size of the user-provided buffer
* offset The file offset
*
* Return:
* The positive non-zero number of bytes read on success, 0 on if an
* end-of-file condition, or -1 on failure with errno set appropriately.
* See read() return values
*
****************************************************************************/
ssize_t pread(int fd, FAR void *buf, size_t nbytes, off_t offset)
{
off_t savepos;
off_t pos;
ssize_t ret;
int errcode;
/* Perform the lseek to the current position. This will not move the
* file pointer, but will return its current setting
*/
savepos = lseek(fd, 0, SEEK_CUR);
if (savepos == (off_t)-1)
{
/* lseek might fail if this if the media is not seekable */
return ERROR;
}
/* Then seek to the correct position in the file */
pos = lseek(fd, offset, SEEK_CUR);
if (pos == (off_t)-1)
{
/* This might fail is the offset is beyond the end of file */
return ERROR;
}
/* Then perform the read operation */
ret = read(fd, buf, nbytes);
errcode = get_errno();
/* Restore the file position */
pos = lseek(fd, savepos, SEEK_CUR);
if (pos == (off_t)-1 && ret >= 0)
{
/* This really should not fail */
return ERROR;
}
set_errno(errcode);
return ret;
}

127
fs/vfs/fs_pwrite.c Normal file
View File

@ -0,0 +1,127 @@
/****************************************************************************
* fs/vfs/fs_pwrite.c
*
* Copyright (C) 2014 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/types.h>
#include <unistd.h>
#include <errno.h>
/****************************************************************************
* Private Functions
****************************************************************************/
/****************************************************************************
* Public Functions
****************************************************************************/
/****************************************************************************
* Name: pwrite
*
* Description:
* The pwrite() function performs the same action as write(), except that
* it writes into a given position without changing the file pointer. The
* first three arguments to pwrite() are the same as write() with the
* addition of a fourth argument offset for the desired position inside
* the file.
*
* NOTE: This function could have been wholly implemented within libc but
* it is not. Why? Because if pwrite were implemented in libc, it would
* require four system calls. If it is implemented within the kernel,
* only three.
*
* Parameters:
* fd file descriptor (or socket descriptor) to write to
* buf Data to write
* nbytes Length of data to write
*
* Return:
* The positive non-zero number of bytes read on success, 0 on if an
* end-of-file condition, or -1 on failure with errno set appropriately.
* See write() return values
*
****************************************************************************/
ssize_t pwrite(int fd, FAR const void *buf, size_t nbytes, off_t offset)
{
off_t savepos;
off_t pos;
ssize_t ret;
int errcode;
/* Perform the lseek to the current position. This will not move the
* file pointer, but will return its current setting
*/
savepos = lseek(fd, 0, SEEK_CUR);
if (savepos == (off_t)-1)
{
/* lseek might fail if this if the media is not seekable */
return ERROR;
}
/* Then seek to the correct position in the file */
pos = lseek(fd, offset, SEEK_CUR);
if (pos == (off_t)-1)
{
/* This might fail is the offset is beyond the end of file */
return ERROR;
}
/* Then perform the write operation */
ret = write(fd, buf, nbytes);
errcode = get_errno();
/* Restore the file position */
pos = lseek(fd, savepos, SEEK_CUR);
if (pos == (off_t)-1 && ret >= 0)
{
/* This really should not fail */
return ERROR;
}
set_errno(errcode);
return ret;
}

6
fs/vfs/fs_read.c
View File

@ -69,7 +69,7 @@
*
* Return:
* The positive non-zero number of bytes read on success, 0 on if an
* end-of-file condition, or -1 on failure withi errno set appropriately.
* end-of-file condition, or -1 on failure with errno set appropriately.
*
****************************************************************************/
@ -101,7 +101,7 @@ ssize_t file_read(FAR struct file *filep, FAR void *buf, size_t nbytes)
else if (inode && inode->u.i_ops && inode->u.i_ops->read)
{
/* Yes.. then let it perform the read. NOTE that for the case of the
* mountpoint, we depend on the read methods bing identical in
* mountpoint, we depend on the read methods being identical in
* signature and position in the operations vtable.
*/
@ -135,7 +135,7 @@ ssize_t file_read(FAR struct file *filep, FAR void *buf, size_t nbytes)
*
* Return:
* The positive non-zero number of bytes read on success, 0 on if an
* end-of-file condition, or -1 on failure withi errno set appropriately.
* end-of-file condition, or -1 on failure with errno set appropriately.
*
****************************************************************************/

2
include/unistd.h
View File

@ -146,6 +146,8 @@ int fsync(int fd);
off_t lseek(int fd, off_t offset, int whence);
ssize_t read(int fd, FAR void *buf, size_t nbytes);
ssize_t write(int fd, FAR const void *buf, size_t nbytes);
ssize_t pread(int fd, FAR void *buf, size_t nbytes, off_t offset);
ssize_t pwrite(int fd, FAR const void *buf, size_t nbytes, off_t offset);
/* Memory management */