nuttx/fs/vfs/fs_lseek.c

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/****************************************************************************
* fs/vfs/fs_lseek.c
*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership. The
* ASF licenses this file to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance with the
* License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
* License for the specific language governing permissions and limitations
* under the License.
*
****************************************************************************/
/****************************************************************************
* Included Files
****************************************************************************/
#include <nuttx/config.h>
#include <sys/types.h>
#include <unistd.h>
#include <sched.h>
#include <errno.h>
#include <assert.h>
#include "inode/inode.h"
/****************************************************************************
* Public Functions
****************************************************************************/
/****************************************************************************
* Name: file_seek
*
* Description:
* This is the internal implementation of lseek. See the comments in
* lseek() for further information.
*
* Input Parameters:
* file File structure instance
* offset Defines the offset to position to
* whence Defines how to use offset
*
* Returned Value:
* The resulting offset on success. A negated errno value is returned on
* any failure (see lseek comments).
*
****************************************************************************/
off_t file_seek(FAR struct file *filep, off_t offset, int whence)
{
FAR struct inode *inode;
off_t ret;
DEBUGASSERT(filep);
inode = filep->f_inode;
/* Invoke the file seek method if available */
if (inode && inode->u.i_ops && inode->u.i_ops->seek)
{
ret = inode->u.i_ops->seek(filep, offset, whence);
if (ret < 0)
{
return ret;
}
}
else
{
/* No... Just set the common file position value */
switch (whence)
{
case SEEK_CUR:
offset += filep->f_pos;
/* FALLTHROUGH */
case SEEK_SET:
if (offset >= 0)
{
filep->f_pos = offset; /* Might be beyond the end-of-file */
break;
}
else
{
return -EINVAL;
}
break;
case SEEK_END:
return -ENOSYS;
default:
return -EINVAL;
}
}
return filep->f_pos;
}
/****************************************************************************
* Name: nx_seek
*
* Description:
* nx_seek() function repositions the offset of the open file associated
* with the file descriptor fd to the argument 'offset' according to the
* directive 'whence'. nx_seek() is an internal OS function. It is
* functionally equivalent to lseek() except that:
*
* - It does not modify the errno variable, and
* - It is not a cancellation point.
*
****************************************************************************/
off_t nx_seek(int fd, off_t offset, int whence)
{
FAR struct file *filep;
off_t ret;
/* Get the file structure corresponding to the file descriptor. */
ret = fs_getfilep(fd, &filep);
if (ret < 0)
{
return ret;
}
DEBUGASSERT(filep != NULL);
/* Then let file_seek do the real work */
return file_seek(filep, offset, whence);
}
/****************************************************************************
* Name: lseek
*
* Description:
* The lseek() function repositions the offset of the open file associated
* with the file descriptor fd to the argument 'offset' according to the
* directive 'whence' as follows:
*
* SEEK_SET
* The offset is set to offset bytes.
* SEEK_CUR
* The offset is set to its current location plus offset bytes.
* SEEK_END
* The offset is set to the size of the file plus offset bytes.
*
* The lseek() function allows the file offset to be set beyond the end of
* the file (but this does not change the size of the file). If data is
* later written at this point, subsequent reads of the data in the gap (a
* "hole") return null bytes ('\0') until data is actually written into the
* gap.
*
* Input Parameters:
* fd File descriptor of device
* offset Defines the offset to position to
* whence Defines how to use offset
*
* Returned Value:
* The resulting offset on success. -1 on failure withi errno set properly:
*
* EBADF fd is not an open file descriptor.
* EINVAL whence is not one of SEEK_SET, SEEK_CUR, SEEK_END; or the
* resulting file offset would be negative, or beyond the end of
* a seekable device.
* EOVERFLOW The resulting file offset cannot be represented in an off_t.
* ESPIPE fd is associated with a pipe, socket, or FIFO.
*
****************************************************************************/
off_t lseek(int fd, off_t offset, int whence)
{
off_t newpos;
/* Let nx_seek do the real work */
newpos = nx_seek(fd, offset, whence);
if (newpos < 0)
{
set_errno(-newpos);
return ERROR;
}
return newpos;
}