/*

 * The partition functions

 *

 * Copyright (C) 2009-2023, Joachim Metz <joachim.metz@gmail.com>

 *

 * Refer to AUTHORS for acknowledgements.

 *

 * This program is free software: you can redistribute it and/or modify

 * it under the terms of the GNU Lesser General Public License as published by

 * the Free Software Foundation, either version 3 of the License, or

 * (at your option) any later version.

 *

 * This program is distributed in the hope that it will be useful,

 * but WITHOUT ANY WARRANTY; without even the implied warranty of

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

 * GNU General Public License for more details.

 *

 * You should have received a copy of the GNU Lesser General Public License

 * along with this program.  If not, see <https://www.gnu.org/licenses/>.

 */

#include <common.h>

#include <memory.h>

#include <types.h>

#include "libvsapm_definitions.h"

#include "libvsapm_io_handle.h"

#include "libvsapm_libbfio.h"

#include "libvsapm_libcerror.h"

#include "libvsapm_libcthreads.h"

#include "libvsapm_libfcache.h"

#include "libvsapm_libfdata.h"

#include "libvsapm_partition.h"

#include "libvsapm_partition_map_entry.h"

#include "libvsapm_sector_data.h"

#include "libvsapm_types.h"

#include "libvsapm_unused.h"

/* Creates a partition

 * Make sure the value partition is referencing, is set to NULL

 * Returns 1 if successful or -1 on error

 */

int libvsapm_partition_initialize(

     libvsapm_partition_t **partition,

     libvsapm_io_handle_t *io_handle,

     libbfio_handle_t *file_io_handle,

     libvsapm_partition_map_entry_t *partition_map_entry,

     libcerror_error_t **error )

{

  libvsapm_internal_partition_t *internal_partition = NULL;

  static char *function                             = "libvsapm_partition_initialize";

  size64_t partition_size                           = 0;

  off64_t partition_offset                          = 0;

  int element_index                                 = 0;

  if( partition == NULL )

  {

    libcerror_error_set(

     error,

     LIBCERROR_ERROR_DOMAIN_ARGUMENTS,

     LIBCERROR_ARGUMENT_ERROR_INVALID_VALUE,

     "%s: invalid partition.",

     function );

    return( -1 );

  }

  if( *partition != NULL )

  {

    libcerror_error_set(

     error,

     LIBCERROR_ERROR_DOMAIN_RUNTIME,

     LIBCERROR_RUNTIME_ERROR_VALUE_ALREADY_SET,

     "%s: invalid partition value already set.",

     function );

    return( -1 );

  }

  if( io_handle == NULL )

  {

    libcerror_error_set(

     error,

     LIBCERROR_ERROR_DOMAIN_ARGUMENTS,

     LIBCERROR_ARGUMENT_ERROR_INVALID_VALUE,

     "%s: invalid IO handle.",

     function );

    return( -1 );

  }

  if( partition_map_entry == NULL )

  {

    libcerror_error_set(

     error,

     LIBCERROR_ERROR_DOMAIN_ARGUMENTS,

     LIBCERROR_ARGUMENT_ERROR_INVALID_VALUE,

     "%s: invalid partition map entry.",

     function );

    return( -1 );

  }

  internal_partition = memory_allocate_structure(

                        libvsapm_internal_partition_t );

  if( internal_partition == NULL )

  {

    libcerror_error_set(

     error,

     LIBCERROR_ERROR_DOMAIN_MEMORY,

     LIBCERROR_MEMORY_ERROR_INSUFFICIENT,

     "%s: unable to create partition.",

     function );

    goto on_error;

  }

  if( memory_set(

       internal_partition,

       0,

       sizeof( libvsapm_internal_partition_t ) ) == NULL )

  {

    libcerror_error_set(

     error,

     LIBCERROR_ERROR_DOMAIN_MEMORY,

     LIBCERROR_MEMORY_ERROR_SET_FAILED,

     "%s: unable to clear partition.",

     function );

    goto on_error;

  }

  if( libvsapm_partition_map_entry_get_sector_number(

       partition_map_entry,

       (uint32_t *) &partition_offset,

       error ) != 1 )

  {

    libcerror_error_set(

     error,

     LIBCERROR_ERROR_DOMAIN_RUNTIME,

     LIBCERROR_RUNTIME_ERROR_GET_FAILED,

     "%s: unable to retrieve partition sector number.",

     function );

    goto on_error;

  }

  partition_offset *= io_handle->bytes_per_sector;

  if( libvsapm_partition_map_entry_get_number_of_sectors(

       partition_map_entry,

       (uint32_t *) &partition_size,

       error ) != 1 )

  {

    libcerror_error_set(

     error,

     LIBCERROR_ERROR_DOMAIN_RUNTIME,

     LIBCERROR_RUNTIME_ERROR_GET_FAILED,

     "%s: unable to retrieve partition number of sectors.",

     function );

    goto on_error;

  }

  partition_size *= io_handle->bytes_per_sector;

  if( libfdata_vector_initialize(

       &( internal_partition->sectors_vector ),

       io_handle->bytes_per_sector,

       NULL,

       NULL,

       NULL,

       (int (*)(intptr_t *, intptr_t *, libfdata_vector_t *, libfdata_cache_t *, int, int, off64_t, size64_t, uint32_t, uint8_t, libcerror_error_t **)) &libvsapm_partition_read_element_data,

       NULL,

       LIBFDATA_DATA_HANDLE_FLAG_NON_MANAGED,

       error ) != 1 )

  {

    libcerror_error_set(

     error,

     LIBCERROR_ERROR_DOMAIN_RUNTIME,

     LIBCERROR_RUNTIME_ERROR_INITIALIZE_FAILED,

     "%s: unable to create sectors vector.",

     function );

    goto on_error;

  }

  if( libfdata_vector_append_segment(

       internal_partition->sectors_vector,

       &element_index,

       0,

       partition_offset,

       partition_size,

       0,

       error ) != 1 )

  {

    libcerror_error_set(

     error,

     LIBCERROR_ERROR_DOMAIN_RUNTIME,

     LIBCERROR_RUNTIME_ERROR_APPEND_FAILED,

     "%s: unable to append segment to sectors vector.",

     function );

    goto on_error;

  }

  if( libfcache_cache_initialize(

       &( internal_partition->sectors_cache ),

       LIBVSAPM_MAXIMUM_CACHE_ENTRIES_SECTORS,

       error ) != 1 )

  {

    libcerror_error_set(

     error,

     LIBCERROR_ERROR_DOMAIN_RUNTIME,

     LIBCERROR_RUNTIME_ERROR_INITIALIZE_FAILED,

     "%s: unable to create sectors cache.",

     function );

    goto on_error;

  }

#if defined( HAVE_MULTI_THREAD_SUPPORT )

  if( libcthreads_read_write_lock_initialize(

       &( internal_partition->read_write_lock ),

       error ) != 1 )

  {

    libcerror_error_set(

     error,

     LIBCERROR_ERROR_DOMAIN_RUNTIME,

     LIBCERROR_RUNTIME_ERROR_INITIALIZE_FAILED,

     "%s: unable to initialize read/write lock.",

     function );

    goto on_error;

  }

#endif

  internal_partition->file_io_handle      = file_io_handle;

  internal_partition->partition_map_entry = partition_map_entry;

  internal_partition->offset              = partition_offset;

  internal_partition->size                = partition_size;

  *partition = (libvsapm_partition_t *) internal_partition;

  return( 1 );

on_error:

  if( internal_partition != NULL )

  {

    memory_free(

     internal_partition );

  }

  return( -1 );

}

/* Frees a partition

 * Returns 1 if successful or -1 on error

 */

int libvsapm_partition_free(

     libvsapm_partition_t **partition,

     libcerror_error_t **error )

{

  libvsapm_internal_partition_t *internal_partition = NULL;

  static char *function                             = "libvsapm_partition_free";

  int result                                        = 1;

  if( partition == NULL )

  {

    libcerror_error_set(

     error,

     LIBCERROR_ERROR_DOMAIN_ARGUMENTS,

     LIBCERROR_ARGUMENT_ERROR_INVALID_VALUE,

     "%s: invalid partition.",

     function );

    return( -1 );

  }

  if( *partition != NULL )

  {

    internal_partition = (libvsapm_internal_partition_t *) *partition;

    *partition         = NULL;

    /* The file_io_handle and partition_map_entry references are freed elsewhere

     */

    if( libfdata_vector_free(

         &( internal_partition->sectors_vector ),

         error ) != 1 )

    {

      libcerror_error_set(

       error,

       LIBCERROR_ERROR_DOMAIN_RUNTIME,

       LIBCERROR_RUNTIME_ERROR_FINALIZE_FAILED,

       "%s: unable to free sectors vector.",

       function );

      result = -1;

    }

    if( libfcache_cache_free(

         &( internal_partition->sectors_cache ),

         error ) != 1 )

    {

      libcerror_error_set(

       error,

       LIBCERROR_ERROR_DOMAIN_RUNTIME,

       LIBCERROR_RUNTIME_ERROR_FINALIZE_FAILED,

       "%s: unable to free sectors cache.",

       function );

      result = -1;

    }

#if defined( HAVE_MULTI_THREAD_SUPPORT )

    if( libcthreads_read_write_lock_free(

         &( internal_partition->read_write_lock ),

         error ) != 1 )

    {

      libcerror_error_set(

       error,

       LIBCERROR_ERROR_DOMAIN_RUNTIME,

       LIBCERROR_RUNTIME_ERROR_FINALIZE_FAILED,

       "%s: unable to free read/write lock.",

       function );

      result = -1;

    }

#endif

    memory_free(

     internal_partition );

  }

  return( result );

}

/* Retrieves the ASCII encoded string of the partition name

 * Returns 1 if successful or -1 on error

 */

int libvsapm_partition_get_name_string(

     libvsapm_partition_t *partition,

     char *string,

     size_t string_size,

     libcerror_error_t **error )

{

  libvsapm_internal_partition_t *internal_partition = NULL;

  static char *function                             = "libvsapm_partition_get_name_string";

  int result                                        = 1;

  if( partition == NULL )

  {

    libcerror_error_set(

     error,

     LIBCERROR_ERROR_DOMAIN_ARGUMENTS,

     LIBCERROR_ARGUMENT_ERROR_INVALID_VALUE,

     "%s: invalid partition.",

     function );

    return( -1 );

  }

  internal_partition = (libvsapm_internal_partition_t *) partition;

#if defined( HAVE_MULTI_THREAD_SUPPORT )

  if( libcthreads_read_write_lock_grab_for_read(

       internal_partition->read_write_lock,

       error ) != 1 )

  {

    libcerror_error_set(

     error,

     LIBCERROR_ERROR_DOMAIN_RUNTIME,

     LIBCERROR_RUNTIME_ERROR_SET_FAILED,

     "%s: unable to grab read/write lock for reading.",

     function );

    return( -1 );

  }

#endif

  if( libvsapm_partition_map_entry_get_name_string(

       internal_partition->partition_map_entry,

       string,

       string_size,

       error ) != 1 )

  {

    libcerror_error_set(

     error,

     LIBCERROR_ERROR_DOMAIN_RUNTIME,

     LIBCERROR_RUNTIME_ERROR_GET_FAILED,

     "%s: unable to retrieve name string.",

     function );

    result = -1;

  }

#if defined( HAVE_MULTI_THREAD_SUPPORT )

  if( libcthreads_read_write_lock_release_for_read(

       internal_partition->read_write_lock,

       error ) != 1 )

  {

    libcerror_error_set(

     error,

     LIBCERROR_ERROR_DOMAIN_RUNTIME,

     LIBCERROR_RUNTIME_ERROR_SET_FAILED,

     "%s: unable to release read/write lock for reading.",

     function );

    return( -1 );

  }

#endif

  return( result );

}

/* Retrieves the ASCII encoded string of the partition type

 * Returns 1 if successful or -1 on error

 */

int libvsapm_partition_get_type_string(

     libvsapm_partition_t *partition,

     char *string,

     size_t string_size,

     libcerror_error_t **error )

{

  libvsapm_internal_partition_t *internal_partition = NULL;

  static char *function                             = "libvsapm_partition_get_type_string";

  int result                                        = 1;

  if( partition == NULL )

  {

    libcerror_error_set(

     error,

     LIBCERROR_ERROR_DOMAIN_ARGUMENTS,

     LIBCERROR_ARGUMENT_ERROR_INVALID_VALUE,

     "%s: invalid partition.",

     function );

    return( -1 );

  }

  internal_partition = (libvsapm_internal_partition_t *) partition;

#if defined( HAVE_MULTI_THREAD_SUPPORT )

  if( libcthreads_read_write_lock_grab_for_read(

       internal_partition->read_write_lock,

       error ) != 1 )

  {

    libcerror_error_set(

     error,

     LIBCERROR_ERROR_DOMAIN_RUNTIME,

     LIBCERROR_RUNTIME_ERROR_SET_FAILED,

     "%s: unable to grab read/write lock for reading.",

     function );

    return( -1 );

  }

#endif

  if( libvsapm_partition_map_entry_get_type_string(

       internal_partition->partition_map_entry,

       string,

       string_size,

       error ) != 1 )

  {

    libcerror_error_set(

     error,

     LIBCERROR_ERROR_DOMAIN_RUNTIME,

     LIBCERROR_RUNTIME_ERROR_GET_FAILED,

     "%s: unable to retrieve type string.",

     function );

    result = -1;

  }

#if defined( HAVE_MULTI_THREAD_SUPPORT )

  if( libcthreads_read_write_lock_release_for_read(

       internal_partition->read_write_lock,

       error ) != 1 )

  {

    libcerror_error_set(

     error,

     LIBCERROR_ERROR_DOMAIN_RUNTIME,

     LIBCERROR_RUNTIME_ERROR_SET_FAILED,

     "%s: unable to release read/write lock for reading.",

     function );

    return( -1 );

  }

#endif

  return( result );

}

/* Retrieves the partition offset relative to the start of the volume

 * Returns 1 if successful or -1 on error

 */

int libvsapm_partition_get_volume_offset(

     libvsapm_partition_t *partition,

     off64_t *volume_offset,

     libcerror_error_t **error )

{

  libvsapm_internal_partition_t *internal_partition = NULL;

  static char *function                             = "libvsapm_partition_get_volume_offset";

  if( partition == NULL )

  {

    libcerror_error_set(

     error,

     LIBCERROR_ERROR_DOMAIN_ARGUMENTS,

     LIBCERROR_ARGUMENT_ERROR_INVALID_VALUE,

     "%s: invalid partition.",

     function );

    return( -1 );

  }

  internal_partition = (libvsapm_internal_partition_t *) partition;

  if( volume_offset == NULL )

  {

    libcerror_error_set(

     error,

     LIBCERROR_ERROR_DOMAIN_ARGUMENTS,

     LIBCERROR_ARGUMENT_ERROR_INVALID_VALUE,

     "%s: invalid volume offset.",

     function );

    return( -1 );

  }

#if defined( HAVE_MULTI_THREAD_SUPPORT )

  if( libcthreads_read_write_lock_grab_for_read(

       internal_partition->read_write_lock,

       error ) != 1 )

  {

    libcerror_error_set(

     error,

     LIBCERROR_ERROR_DOMAIN_RUNTIME,

     LIBCERROR_RUNTIME_ERROR_SET_FAILED,

     "%s: unable to grab read/write lock for reading.",

     function );

    return( -1 );

  }

#endif

  *volume_offset = internal_partition->offset;

#if defined( HAVE_MULTI_THREAD_SUPPORT )

  if( libcthreads_read_write_lock_release_for_read(

       internal_partition->read_write_lock,

       error ) != 1 )

  {

    libcerror_error_set(

     error,

     LIBCERROR_ERROR_DOMAIN_RUNTIME,

     LIBCERROR_RUNTIME_ERROR_SET_FAILED,

     "%s: unable to release read/write lock for reading.",

     function );

    return( -1 );

  }

#endif

  return( 1 );

}

/* Retrieves the partition status flags

 * Returns 1 if successful or -1 on error

 */

int libvsapm_partition_get_status_flags(

     libvsapm_partition_t *partition,

     uint32_t *status_flags,

     libcerror_error_t **error )

{

  libvsapm_internal_partition_t *internal_partition = NULL;

  static char *function                             = "libvsapm_partition_get_status_flags";

  int result                                        = 1;

  if( partition == NULL )

  {

    libcerror_error_set(

     error,

     LIBCERROR_ERROR_DOMAIN_ARGUMENTS,

     LIBCERROR_ARGUMENT_ERROR_INVALID_VALUE,

     "%s: invalid partition.",

     function );

    return( -1 );

  }

  internal_partition = (libvsapm_internal_partition_t *) partition;

#if defined( HAVE_MULTI_THREAD_SUPPORT )

  if( libcthreads_read_write_lock_grab_for_read(

       internal_partition->read_write_lock,

       error ) != 1 )

  {

    libcerror_error_set(

     error,

     LIBCERROR_ERROR_DOMAIN_RUNTIME,

     LIBCERROR_RUNTIME_ERROR_SET_FAILED,

     "%s: unable to grab read/write lock for reading.",

     function );

    return( -1 );

  }

#endif

  if( libvsapm_partition_map_entry_get_status_flags(

       internal_partition->partition_map_entry,

       status_flags,

       error ) != 1 )

  {

    libcerror_error_set(

     error,

     LIBCERROR_ERROR_DOMAIN_RUNTIME,

     LIBCERROR_RUNTIME_ERROR_GET_FAILED,

     "%s: unable to retrieve status flags.",

     function );

    result = -1;

  }

#if defined( HAVE_MULTI_THREAD_SUPPORT )

  if( libcthreads_read_write_lock_release_for_read(

       internal_partition->read_write_lock,

       error ) != 1 )

  {

    libcerror_error_set(

     error,

     LIBCERROR_ERROR_DOMAIN_RUNTIME,

     LIBCERROR_RUNTIME_ERROR_SET_FAILED,

     "%s: unable to release read/write lock for reading.",

     function );

    return( -1 );

  }

#endif

  return( result );

}

/* Reads (partition) data at the current offset into a buffer using a Basic File IO (bfio) handle

 * This function is not multi-thread safe acquire write lock before call

 * Returns the number of bytes read or -1 on error

 */

ssize_t libvsapm_internal_partition_read_buffer_from_file_io_handle(

         libvsapm_internal_partition_t *internal_partition,

         libbfio_handle_t *file_io_handle,

         void *buffer,

         size_t buffer_size,

         libcerror_error_t **error )

{

  libvsapm_sector_data_t *sector_data = NULL;

  static char *function               = "libvsapm_internal_partition_read_buffer_from_file_io_handle";

  off64_t current_offset              = 0;

  off64_t element_data_offset         = 0;

  size_t buffer_offset                = 0;

  size_t read_size                    = 0;

  if( internal_partition == NULL )

  {

    libcerror_error_set(

     error,

     LIBCERROR_ERROR_DOMAIN_ARGUMENTS,

     LIBCERROR_ARGUMENT_ERROR_INVALID_VALUE,

     "%s: invalid partition.",

     function );

    return( -1 );

  }

  if( internal_partition->current_offset < 0 )

  {

    libcerror_error_set(

     error,

     LIBCERROR_ERROR_DOMAIN_RUNTIME,

     LIBCERROR_RUNTIME_ERROR_VALUE_OUT_OF_BOUNDS,

     "%s: invalid partition - current offset value out of bounds.",

     function );

    return( -1 );

  }

  if( buffer == NULL )

  {

    libcerror_error_set(

     error,

     LIBCERROR_ERROR_DOMAIN_ARGUMENTS,

     LIBCERROR_ARGUMENT_ERROR_INVALID_VALUE,

     "%s: invalid buffer.",

     function );

    return( -1 );

  }

  if( buffer_size > (size_t) SSIZE_MAX )

  {

    libcerror_error_set(

     error,

     LIBCERROR_ERROR_DOMAIN_ARGUMENTS,

     LIBCERROR_ARGUMENT_ERROR_VALUE_EXCEEDS_MAXIMUM,

     "%s: invalid buffer size value exceeds maximum.",

     function );

    return( -1 );

  }

  if( buffer_size == 0 )

  {

    return( 0 );

  }

  if( (size64_t) internal_partition->current_offset >= internal_partition->size )

  {

    return( 0 );

  }

  if( (size64_t) buffer_size > ( internal_partition->size - internal_partition->current_offset ) )

  {

    buffer_size = (size_t) ( internal_partition->size - internal_partition->current_offset );

  }

  current_offset = internal_partition->current_offset;

  while( buffer_size > 0 )

  {

    if( libfdata_vector_get_element_value_at_offset(

         internal_partition->sectors_vector,

         (intptr_t *) file_io_handle,

         (libfdata_cache_t *) internal_partition->sectors_cache,

         current_offset,

         &element_data_offset,

         (intptr_t **) &sector_data,

         0,

         error ) != 1 )

    {

      libcerror_error_set(

       error,

       LIBCERROR_ERROR_DOMAIN_RUNTIME,

       LIBCERROR_RUNTIME_ERROR_GET_FAILED,

       "%s: unable to retrieve sector data at offset: %" PRIi64 " (0x%08" PRIx64 ").",

       function,

       current_offset,

       current_offset );

      return( -1 );

    }

    if( sector_data == NULL )

    {

      libcerror_error_set(

       error,

       LIBCERROR_ERROR_DOMAIN_RUNTIME,

       LIBCERROR_RUNTIME_ERROR_VALUE_MISSING,

       "%s: missing sector data.",

       function );

      return( -1 );

    }

    read_size = sector_data->data_size - (size_t) element_data_offset;

    if( buffer_size < read_size )

    {

      read_size = buffer_size;

    }

    if( memory_copy(

         &( ( (uint8_t *) buffer )[ buffer_offset ] ),

         &( sector_data->data[ element_data_offset ] ),

         read_size ) == NULL )

    {

      libcerror_error_set(

       error,

       LIBCERROR_ERROR_DOMAIN_MEMORY,

       LIBCERROR_MEMORY_ERROR_COPY_FAILED,

       "%s: unable to copy sector data.",

       function );

      return( -1 );

    }

    current_offset += read_size;

    buffer_offset  += read_size;

    buffer_size    -= read_size;

  }

  internal_partition->current_offset = current_offset;

  return( (ssize_t) buffer_offset );

}

/* Reads (partition) data at the current offset into a buffer

 * Returns the number of bytes read or -1 on error

 */

ssize_t libvsapm_partition_read_buffer(

         libvsapm_partition_t *partition,

         void *buffer,

         size_t buffer_size,

         libcerror_error_t **error )

{

  libvsapm_internal_partition_t *internal_partition = NULL;

  static char *function                             = "libvsapm_partition_read_buffer";

  ssize_t read_count                                = 0;

  if( partition == NULL )

  {

    libcerror_error_set(

     error,

     LIBCERROR_ERROR_DOMAIN_ARGUMENTS,

     LIBCERROR_ARGUMENT_ERROR_INVALID_VALUE,

     "%s: invalid partition.",

     function );

    return( -1 );

  }

  internal_partition = (libvsapm_internal_partition_t *) partition;

#if defined( HAVE_MULTI_THREAD_SUPPORT )

  if( libcthreads_read_write_lock_grab_for_write(

       internal_partition->read_write_lock,

       error ) != 1 )

  {

    libcerror_error_set(

     error,

     LIBCERROR_ERROR_DOMAIN_RUNTIME,

     LIBCERROR_RUNTIME_ERROR_SET_FAILED,

     "%s: unable to grab read/write lock for writing.",

     function );

    return( -1 );

  }

#endif

  read_count = libvsapm_internal_partition_read_buffer_from_file_io_handle(

          internal_partition,

          internal_partition->file_io_handle,

          buffer,

          buffer_size,

          error );

  if( read_count == -1 )

  {

    libcerror_error_set(

     error,

     LIBCERROR_ERROR_DOMAIN_IO,

     LIBCERROR_IO_ERROR_READ_FAILED,

     "%s: unable to read buffer from partition.",

     function );

    read_count = -1;

  }

#if defined( HAVE_MULTI_THREAD_SUPPORT )

  if( libcthreads_read_write_lock_release_for_write(

       internal_partition->read_write_lock,

       error ) != 1 )

  {

    libcerror_error_set(

     error,

     LIBCERROR_ERROR_DOMAIN_RUNTIME,

     LIBCERROR_RUNTIME_ERROR_SET_FAILED,

     "%s: unable to release read/write lock for writing.",

     function );

    return( -1 );

  }

#endif

  return( read_count );

}

/* Reads (partition) data at a specific offset

 * Returns the number of bytes read or -1 on error

 */

ssize_t libvsapm_partition_read_buffer_at_offset(

         libvsapm_partition_t *partition,

         void *buffer,

         size_t buffer_size,

         off64_t offset,

         libcerror_error_t **error )

{

  libvsapm_internal_partition_t *internal_partition = NULL;

  static char *function                             = "libvsapm_partition_read_buffer_at_offset";

  ssize_t read_count                                = 0;

  if( partition == NULL )

  {

    libcerror_error_set(

     error,

     LIBCERROR_ERROR_DOMAIN_ARGUMENTS,

     LIBCERROR_ARGUMENT_ERROR_INVALID_VALUE,

     "%s: invalid partition.",

     function );

    return( -1 );

  }

  internal_partition = (libvsapm_internal_partition_t *) partition;

#if defined( HAVE_MULTI_THREAD_SUPPORT )

  if( libcthreads_read_write_lock_grab_for_write(

       internal_partition->read_write_lock,

       error ) != 1 )

  {

    libcerror_error_set(

     error,

     LIBCERROR_ERROR_DOMAIN_RUNTIME,

     LIBCERROR_RUNTIME_ERROR_SET_FAILED,

     "%s: unable to grab read/write lock for writing.",

     function );

    return( -1 );

  }

#endif

  if( libvsapm_internal_partition_seek_offset(

       internal_partition,

       offset,

       SEEK_SET,

       error ) == -1 )

  {

    libcerror_error_set(

     error,

     LIBCERROR_ERROR_DOMAIN_IO,

     LIBCERROR_IO_ERROR_SEEK_FAILED,

     "%s: unable to seek offset.",

     function );

    goto on_error;

  }

  read_count = libvsapm_internal_partition_read_buffer_from_file_io_handle(

          internal_partition,

          internal_partition->file_io_handle,

          buffer,

          buffer_size,

          error );

  if( read_count == -1 )

  {

    libcerror_error_set(

     error,

     LIBCERROR_ERROR_DOMAIN_IO,

     LIBCERROR_IO_ERROR_READ_FAILED,

     "%s: unable to read buffer.",

     function );

    goto on_error;

  }

#if defined( HAVE_MULTI_THREAD_SUPPORT )

  if( libcthreads_read_write_lock_release_for_write(

       internal_partition->read_write_lock,

       error ) != 1 )

  {

    libcerror_error_set(

     error,

     LIBCERROR_ERROR_DOMAIN_RUNTIME,

     LIBCERROR_RUNTIME_ERROR_SET_FAILED,

     "%s: unable to release read/write lock for writing.",

     function );

    return( -1 );

  }

#endif