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incubator-nuttx/fs/nxffs/nxffs_read.c

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/****************************************************************************
* fs/nxffs/nxffs_read.c
*
* Copyright (C) 2011 Gregory Nutt. All rights reserved.
* Author: Gregory Nutt <gnutt@nuttx.org>
*
* References: Linux/Documentation/filesystems/romfs.txt
*
* 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 <string.h>
#include <fcntl.h>
#include <crc32.h>
#include <assert.h>
#include <errno.h>
#include <debug.h>
#include <nuttx/fs/fs.h>
#include <nuttx/mtd.h>
#include "nxffs.h"
/****************************************************************************
* Pre-processor Definitions
****************************************************************************/
/****************************************************************************
* Public Types
****************************************************************************/
/****************************************************************************
* Public Variables
****************************************************************************/
/****************************************************************************
* Private Functions
****************************************************************************/
/****************************************************************************
* Name: nxffs_rdseek
*
* Description:
* Seek to the file position before read or write access. Note that the
* simplier nxffs_ioseek() cannot be used for this purpose. File offsets
* are not easily mapped to FLASH offsets due to intervening block and
* data headers.
*
* Input Parameters:
* volume - Describes the current volume
* entry - Describes the open inode
* fpos - The desired file position
* blkentry - Describes the block entry that we are positioned in
*
****************************************************************************/
static ssize_t nxffs_rdseek(FAR struct nxffs_volume_s *volume,
FAR struct nxffs_entry_s *entry,
off_t fpos,
FAR struct nxffs_blkentry_s *blkentry)
{
size_t datstart;
size_t datend;
off_t offset;
int ret;
/* The initial FLASH offset will be the offset to first data block of
* the inode
*/
offset = entry->doffset;
if (offset == 0)
{
/* Zero length files will have no data blocks */
return -ENOSPC;
}
/* Loop until we read the data block containing the desired position */
datend = 0;
do
{
/* Check if the next data block contains the sought after file position */
ret = nxffs_nextblock(volume, offset, blkentry);
if (ret < 0)
{
fdbg("nxffs_nextblock failed: %d\n", -ret);
return ret;
}
/* Get the range of data offsets for this data block */
datstart = datend;
datend += blkentry->datlen;
/* Offset to search for the the next data block */
offset = blkentry->hoffset + SIZEOF_NXFFS_DATA_HDR + blkentry->datlen;
}
while (datend <= fpos);
/* Return the offset to the data within the current data block */
blkentry->foffset = fpos - datstart;
nxffs_ioseek(volume, blkentry->hoffset + SIZEOF_NXFFS_DATA_HDR + blkentry->foffset);
return OK;
}
/****************************************************************************
* Public Functions
****************************************************************************/
/****************************************************************************
* Name: nxffs_read
*
* Description:
* This is an implementation of the NuttX standard file system read
* method.
*
****************************************************************************/
ssize_t nxffs_read(FAR struct file *filep, FAR char *buffer, size_t buflen)
{
FAR struct nxffs_volume_s *volume;
FAR struct nxffs_ofile_s *ofile;
struct nxffs_blkentry_s blkentry;
ssize_t total;
size_t available;
size_t readsize;
int ret;
fvdbg("Read %d bytes from offset %d\n", buflen, filep->f_pos);
/* Sanity checks */
DEBUGASSERT(filep->f_priv != NULL && filep->f_inode != NULL);
/* Recover the open file state from the struct file instance */
ofile = (FAR struct nxffs_ofile_s *)filep->f_priv;
/* Recover the volume state from the open file */
volume = (FAR struct nxffs_volume_s *)filep->f_inode->i_private;
DEBUGASSERT(volume != NULL);
/* Get exclusive access to the volume. Note that the volume exclsem
* protects the open file list.
*/
ret = sem_wait(&volume->exclsem);
if (ret != OK)
{
ret = -errno;
fdbg("sem_wait failed: %d\n", ret);
goto errout;
}
/* Check if the file was opened with read access */
if ((ofile->oflags & O_RDOK) == 0)
{
fdbg("File not open for read access\n");
ret = -EACCES;
goto errout_with_semaphore;
}
/* Loop until all bytes have been read */
for (total = 0; total < buflen; )
{
/* Don't seek past the end of the file */
if (filep->f_pos >= ofile->entry.datlen)
{
/* Return the partial read */
filep->f_pos = ofile->entry.datlen;
break;
}
/* Seek to the current file offset */
ret = nxffs_rdseek(volume, &ofile->entry, filep->f_pos, &blkentry);
if (ret < 0)
{
fdbg("nxffs_rdseek failed: %d\n", -ret);
ret = -EACCES;
goto errout_with_semaphore;
}
/* How many bytes are available at this offset */
available = blkentry.datlen - blkentry.foffset;
/* Don't read more than we need to */
readsize = buflen - total;
if (readsize > available)
{
readsize = available;
}
/* Read data from that file offset */
memcpy(&buffer[total], &volume->cache[volume->iooffset], readsize);
/* Update the file offset */
filep->f_pos += readsize;
total += readsize;
}
sem_post(&volume->exclsem);
return total;
errout_with_semaphore:
sem_post(&volume->exclsem);
errout:
return (ssize_t)ret;
}
/****************************************************************************
* Name: nxffs_nextblock
*
* Description:
* Search for the next valid data block starting at the provided
* FLASH offset.
*
* Input Parameters:
* volume - Describes the NXFFS volume.
* datlen - A memory location to return the data block length.
*
* Returned Value:
* Zero is returned on success. Otherwise, a negated errno is returned
* that indicates the nature of the failure.
*
****************************************************************************/
int nxffs_nextblock(FAR struct nxffs_volume_s *volume, off_t offset,
FAR struct nxffs_blkentry_s *blkentry)
{
int nmagic;
int ch;
int nerased;
int ret;
/* Seek to the first FLASH offset provided by the caller. */
nxffs_ioseek(volume, offset);
/* Skip the block header */
if (volume->iooffset < SIZEOF_NXFFS_BLOCK_HDR)
{
volume->iooffset = SIZEOF_NXFFS_BLOCK_HDR;
}
/* Then begin searching */
nerased = 0;
nmagic = 0;
for (;;)
{
/* Read the next character */
ch = nxffs_getc(volume, SIZEOF_NXFFS_DATA_HDR - nmagic);
if (ch < 0)
{
fvdbg("nxffs_getc failed: %d\n", -ch);
return ch;
}
/* Check for another erased byte */
else if (ch == CONFIG_NXFFS_ERASEDSTATE)
{
/* If we have encountered NXFFS_NERASED number of consecutive
* erased bytes, then presume we have reached the end of valid
* data.
*/
if (++nerased >= NXFFS_NERASED)
{
fvdbg("No entry found\n");
return -ENOENT;
}
}
else
{
nerased = 0;
/* Check for the magic sequence indicating the start of an NXFFS
* data block or start of the next inode. There is the possibility
* of this magic sequnce occurring in FLASH data. However, the
* data block CRC should distinguish between real NXFFS data blocks
* headers and such false alarms.
*/
if (ch != g_datamagic[nmagic])
{
/* Ooops... this is the not the right character for the magic
* Sequence. Check if we need to restart or to cancel the sequence:
*/
if (ch == g_datamagic[0])
{
nmagic = 1;
}
else
{
nmagic = 0;
}
}
else if (nmagic < NXFFS_MAGICSIZE - 1)
{
/* We have one more character in the magic sequence */
nmagic++;
}
/* We have found the magic sequence in the FLASH data that may
* indicate the beginning of an NXFFS data block.
*/
else
{
/* The offset to the header must be 4 bytes before the current
* FLASH seek location.
*/
blkentry->hoffset = nxffs_iotell(volume) - NXFFS_MAGICSIZE;
/* Read the block header and verify the block at that address */
ret = nxffs_rdblkhdr(volume, blkentry->hoffset, &blkentry->datlen);
if (ret == OK)
{
fvdbg("Found a valid data block, offset: %d datlen: %d\n",
blkentry->hoffset, blkentry->datlen);
return OK;
}
/* False alarm.. Restore the volume cache position (that was
* destroyed by nxfs_rdblkhdr()) and keep looking.
*/
nxffs_ioseek(volume, blkentry->hoffset + NXFFS_MAGICSIZE);
nmagic = 0;
}
}
}
/* We won't get here, but to keep some compilers happy: */
return -ENOENT;
}
/****************************************************************************
* Name: nxffs_rdblkhdr
*
* Description:
* Read and verify the data block header at the specified offset.
*
* Input Parameters:
* volume - Describes the current volume.
* offset - The byte offset from the beginning of FLASH where the data block
* header is expected.
* datlen - A memory location to return the data block length.
*
* Returned Value:
* Zero on success. Otherwise, a negated errno value is returned
* indicating the nature of the failure.
*
****************************************************************************/
int nxffs_rdblkhdr(FAR struct nxffs_volume_s *volume, off_t offset,
FAR uint16_t *datlen)
{
struct nxffs_data_s blkhdr;
uint32_t ecrc;
uint32_t crc;
uint16_t doffset;
uint16_t dlen;
int ret;
/* Make sure the the block containing the data block header is in the cache */
nxffs_ioseek(volume, offset);
ret = nxffs_rdcache(volume, volume->ioblock);
if (ret < 0)
{
fvdbg("Failed to read data into cache: %d\n", ret);
return ret;
}
/* Read the header at the FLASH offset */
doffset = volume->iooffset;
memcpy(&blkhdr, &volume->cache[doffset], SIZEOF_NXFFS_DATA_HDR);
/* Extract the data length */
dlen = nxffs_rdle16(blkhdr.datlen);
/* Get the offset to the beginning of the data */
doffset += SIZEOF_NXFFS_DATA_HDR;
/* Make sure that all of the data fits within the block */
if ((uint32_t)doffset + (uint32_t)dlen > (uint32_t)volume->geo.blocksize)
{
fdbg("Data length=%d is unreasonable at offset=%d\n", dlen, doffset);
return -EIO;
}
/* Extract the expected CRC and calculate the CRC of the data block */
ecrc = nxffs_rdle32(blkhdr.crc);
nxffs_wrle32(blkhdr.crc, 0);
crc = crc32((FAR const uint8_t *)&blkhdr, SIZEOF_NXFFS_DATA_HDR);
crc = crc32part(&volume->cache[doffset], dlen, crc);
if (crc != ecrc)
{
fdbg("CRC failure\n");
return -EIO;
}
/* Looks good! Return the data length and success */
*datlen = dlen;
return OK;
}
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