wic: add FIEMAP and SEEK_HOLE / SEEK_DATA APIs

In order to make wic images sparse set of APIs has been copied
from bmap-tools project.

filemap.py module is taken from bmap-tools project:
https://github.com/01org/bmap-tools/blob/master/bmaptools/Filemap.py
It implements two ways of get information about file block: FIEMAP
ioctl and the 'SEEK_HOLE / SEEK_DATA' features of the file seek
syscall.

Note that this module will be removed as soon as bmaptool utility
supports copying sparse source file into destination file (this is
already agreed with the maintainer of bmap-tools project).

[YOCTO #9099]

Signed-off-by: Ed Bartosh <ed.bartosh@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

1 files changed, 531 insertions, 0 deletions

diff --git a/scripts/lib/wic/filemap.py b/scripts/lib/wic/filemap.py
new file mode 100644
index 0000000000..1d04328322
--- /dev/null
+++ b/scripts/lib/wic/filemap.py
@@ -0,0 +1,531 @@
+# Copyright (c) 2012 Intel, Inc.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License, version 2,
+# as published by the Free Software Foundation.
+#
+# 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.
+
+"""
+This module implements python implements a way to get file block. Two methods
+are supported - the FIEMAP ioctl and the 'SEEK_HOLE / SEEK_DATA' features of
+the file seek syscall. The former is implemented by the 'FilemapFiemap' class,
+the latter is implemented by the 'FilemapSeek' class. Both classes provide the
+same API. The 'filemap' function automatically selects which class can be used
+and returns an instance of the class.
+"""
+
+# Disable the following pylint recommendations:
+#   * Too many instance attributes (R0902)
+# pylint: disable=R0902
+
+import os
+import struct
+import array
+import fcntl
+import tempfile
+import logging
+
+def get_block_size(file_obj):
+    """
+    Returns block size for file object 'file_obj'. Errors are indicated by the
+    'IOError' exception.
+    """
+
+    from fcntl import ioctl
+    import struct
+
+    # Get the block size of the host file-system for the image file by calling
+    # the FIGETBSZ ioctl (number 2).
+    binary_data = ioctl(file_obj, 2, struct.pack('I', 0))
+    return struct.unpack('I', binary_data)[0]
+
+class ErrorNotSupp(Exception):
+    """
+    An exception of this type is raised when the 'FIEMAP' or 'SEEK_HOLE' feature
+    is not supported either by the kernel or the file-system.
+    """
+    pass
+
+class Error(Exception):
+    """A class for all the other exceptions raised by this module."""
+    pass
+
+
+class _FilemapBase(object):
+    """
+    This is a base class for a couple of other classes in this module. This
+    class simply performs the common parts of the initialization process: opens
+    the image file, gets its size, etc. The 'log' parameter is the logger object
+    to use for printing messages.
+    """
+
+    def __init__(self, image, log=None):
+        """
+        Initialize a class instance. The 'image' argument is full path to the
+        file or file object to operate on.
+        """
+
+        self._log = log
+        if self._log is None:
+            self._log = logging.getLogger(__name__)
+
+        self._f_image_needs_close = False
+
+        if hasattr(image, "fileno"):
+            self._f_image = image
+            self._image_path = image.name
+        else:
+            self._image_path = image
+            self._open_image_file()
+
+        try:
+            self.image_size = os.fstat(self._f_image.fileno()).st_size
+        except IOError as err:
+            raise Error("cannot get information about file '%s': %s"
+                        % (self._f_image.name, err))
+
+        try:
+            self.block_size = get_block_size(self._f_image)
+        except IOError as err:
+            raise Error("cannot get block size for '%s': %s"
+                        % (self._image_path, err))
+
+        self.blocks_cnt = self.image_size + self.block_size - 1
+        self.blocks_cnt /= self.block_size
+
+        try:
+            self._f_image.flush()
+        except IOError as err:
+            raise Error("cannot flush image file '%s': %s"
+                        % (self._image_path, err))
+
+        try:
+            os.fsync(self._f_image.fileno()),
+        except OSError as err:
+            raise Error("cannot synchronize image file '%s': %s "
+                        % (self._image_path, err.strerror))
+
+        self._log.debug("opened image \"%s\"" % self._image_path)
+        self._log.debug("block size %d, blocks count %d, image size %d"
+                        % (self.block_size, self.blocks_cnt, self.image_size))
+
+    def __del__(self):
+        """The class destructor which just closes the image file."""
+        if self._f_image_needs_close:
+            self._f_image.close()
+
+    def _open_image_file(self):
+        """Open the image file."""
+        try:
+            self._f_image = open(self._image_path, 'rb')
+        except IOError as err:
+            raise Error("cannot open image file '%s': %s"
+                        % (self._image_path, err))
+
+        self._f_image_needs_close = True
+
+    def block_is_mapped(self, block): # pylint: disable=W0613,R0201
+        """
+        This method has has to be implemented by child classes. It returns
+        'True' if block number 'block' of the image file is mapped and 'False'
+        otherwise.
+        """
+
+        raise Error("the method is not implemented")
+
+    def block_is_unmapped(self, block): # pylint: disable=W0613,R0201
+        """
+        This method has has to be implemented by child classes. It returns
+        'True' if block number 'block' of the image file is not mapped (hole)
+        and 'False' otherwise.
+        """
+
+        raise Error("the method is not implemented")
+
+    def get_mapped_ranges(self, start, count): # pylint: disable=W0613,R0201
+        """
+        This method has has to be implemented by child classes. This is a
+        generator which yields ranges of mapped blocks in the file. The ranges
+        are tuples of 2 elements: [first, last], where 'first' is the first
+        mapped block and 'last' is the last mapped block.
+
+        The ranges are yielded for the area of the file of size 'count' blocks,
+        starting from block 'start'.
+        """
+
+        raise Error("the method is not implemented")
+
+    def get_unmapped_ranges(self, start, count): # pylint: disable=W0613,R0201
+        """
+        This method has has to be implemented by child classes. Just like
+        'get_mapped_ranges()', but yields unmapped block ranges instead
+        (holes).
+        """
+
+        raise Error("the method is not implemented")
+
+
+# The 'SEEK_HOLE' and 'SEEK_DATA' options of the file seek system call
+_SEEK_DATA = 3
+_SEEK_HOLE = 4
+
+def _lseek(file_obj, offset, whence):
+    """This is a helper function which invokes 'os.lseek' for file object
+    'file_obj' and with specified 'offset' and 'whence'. The 'whence'
+    argument is supposed to be either '_SEEK_DATA' or '_SEEK_HOLE'. When
+    there is no more data or hole starting from 'offset', this function
+    returns '-1'.  Otherwise the data or hole position is returned."""
+
+    try:
+        return os.lseek(file_obj.fileno(), offset, whence)
+    except OSError as err:
+        # The 'lseek' system call returns the ENXIO if there is no data or
+        # hole starting from the specified offset.
+        if err.errno == os.errno.ENXIO:
+            return -1
+        elif err.errno == os.errno.EINVAL:
+            raise ErrorNotSupp("the kernel or file-system does not support "
+                               "\"SEEK_HOLE\" and \"SEEK_DATA\"")
+        else:
+            raise
+
+class FilemapSeek(_FilemapBase):
+    """
+    This class uses the 'SEEK_HOLE' and 'SEEK_DATA' to find file block mapping.
+    Unfortunately, the current implementation requires the caller to have write
+    access to the image file.
+    """
+
+    def __init__(self, image, log=None):
+        """Refer the '_FilemapBase' class for the documentation."""
+
+        # Call the base class constructor first
+        _FilemapBase.__init__(self, image, log)
+        self._log.debug("FilemapSeek: initializing")
+
+        self._probe_seek_hole()
+
+    def _probe_seek_hole(self):
+        """
+        Check whether the system implements 'SEEK_HOLE' and 'SEEK_DATA'.
+        Unfortunately, there seems to be no clean way for detecting this,
+        because often the system just fakes them by just assuming that all
+        files are fully mapped, so 'SEEK_HOLE' always returns EOF and
+        'SEEK_DATA' always returns the requested offset.
+
+        I could not invent a better way of detecting the fake 'SEEK_HOLE'
+        implementation than just to create a temporary file in the same
+        directory where the image file resides. It would be nice to change this
+        to something better.
+        """
+
+        directory = os.path.dirname(self._image_path)
+
+        try:
+            tmp_obj = tempfile.TemporaryFile("w+", dir=directory)
+        except IOError as err:
+            raise ErrorNotSupp("cannot create a temporary in \"%s\": %s"
+                              % (directory, err))
+
+        try:
+            os.ftruncate(tmp_obj.fileno(), self.block_size)
+        except OSError as err:
+            raise ErrorNotSupp("cannot truncate temporary file in \"%s\": %s"
+                               % (directory, err))
+
+        offs = _lseek(tmp_obj, 0, _SEEK_HOLE)
+        if offs != 0:
+            # We are dealing with the stub 'SEEK_HOLE' implementation which
+            # always returns EOF.
+            self._log.debug("lseek(0, SEEK_HOLE) returned %d" % offs)
+            raise ErrorNotSupp("the file-system does not support "
+                               "\"SEEK_HOLE\" and \"SEEK_DATA\" but only "
+                               "provides a stub implementation")
+
+        tmp_obj.close()
+
+    def block_is_mapped(self, block):
+        """Refer the '_FilemapBase' class for the documentation."""
+        offs = _lseek(self._f_image, block * self.block_size, _SEEK_DATA)
+        if offs == -1:
+            result = False
+        else:
+            result = (offs / self.block_size == block)
+
+        self._log.debug("FilemapSeek: block_is_mapped(%d) returns %s"
+                        % (block, result))
+        return result
+
+    def block_is_unmapped(self, block):
+        """Refer the '_FilemapBase' class for the documentation."""
+        return not self.block_is_mapped(block)
+
+    def _get_ranges(self, start, count, whence1, whence2):
+        """
+        This function implements 'get_mapped_ranges()' and
+        'get_unmapped_ranges()' depending on what is passed in the 'whence1'
+        and 'whence2' arguments.
+        """
+
+        assert whence1 != whence2
+        end = start * self.block_size
+        limit = end + count * self.block_size
+
+        while True:
+            start = _lseek(self._f_image, end, whence1)
+            if start == -1 or start >= limit or start == self.image_size:
+                break
+
+            end = _lseek(self._f_image, start, whence2)
+            if end == -1 or end == self.image_size:
+                end = self.blocks_cnt * self.block_size
+            if end > limit:
+                end = limit
+
+            start_blk = start / self.block_size
+            end_blk = end / self.block_size - 1
+            self._log.debug("FilemapSeek: yielding range (%d, %d)"
+                            % (start_blk, end_blk))
+            yield (start_blk, end_blk)
+
+    def get_mapped_ranges(self, start, count):
+        """Refer the '_FilemapBase' class for the documentation."""
+        self._log.debug("FilemapSeek: get_mapped_ranges(%d,  %d(%d))"
+                        % (start, count, start + count - 1))
+        return self._get_ranges(start, count, _SEEK_DATA, _SEEK_HOLE)
+
+    def get_unmapped_ranges(self, start, count):
+        """Refer the '_FilemapBase' class for the documentation."""
+        self._log.debug("FilemapSeek: get_unmapped_ranges(%d,  %d(%d))"
+                        % (start, count, start + count - 1))
+        return self._get_ranges(start, count, _SEEK_HOLE, _SEEK_DATA)
+
+
+# Below goes the FIEMAP ioctl implementation, which is not very readable
+# because it deals with the rather complex FIEMAP ioctl. To understand the
+# code, you need to know the FIEMAP interface, which is documented in the
+# "Documentation/filesystems/fiemap.txt" file in the Linux kernel sources.
+
+# Format string for 'struct fiemap'
+_FIEMAP_FORMAT = "=QQLLLL"
+# sizeof(struct fiemap)
+_FIEMAP_SIZE = struct.calcsize(_FIEMAP_FORMAT)
+# Format string for 'struct fiemap_extent'
+_FIEMAP_EXTENT_FORMAT = "=QQQQQLLLL"
+# sizeof(struct fiemap_extent)
+_FIEMAP_EXTENT_SIZE = struct.calcsize(_FIEMAP_EXTENT_FORMAT)
+# The FIEMAP ioctl number
+_FIEMAP_IOCTL = 0xC020660B
+# This FIEMAP ioctl flag which instructs the kernel to sync the file before
+# reading the block map
+_FIEMAP_FLAG_SYNC = 0x00000001
+# Size of the buffer for 'struct fiemap_extent' elements which will be used
+# when invoking the FIEMAP ioctl. The larger is the buffer, the less times the
+# FIEMAP ioctl will be invoked.
+_FIEMAP_BUFFER_SIZE = 256 * 1024
+
+class FilemapFiemap(_FilemapBase):
+    """
+    This class provides API to the FIEMAP ioctl. Namely, it allows to iterate
+    over all mapped blocks and over all holes.
+
+    This class synchronizes the image file every time it invokes the FIEMAP
+    ioctl in order to work-around early FIEMAP implementation kernel bugs.
+    """
+
+    def __init__(self, image, log=None):
+        """
+        Initialize a class instance. The 'image' argument is full the file
+        object to operate on.
+        """
+
+        # Call the base class constructor first
+        _FilemapBase.__init__(self, image, log)
+        self._log.debug("FilemapFiemap: initializing")
+
+        self._buf_size = _FIEMAP_BUFFER_SIZE
+
+        # Calculate how many 'struct fiemap_extent' elements fit the buffer
+        self._buf_size -= _FIEMAP_SIZE
+        self._fiemap_extent_cnt = self._buf_size / _FIEMAP_EXTENT_SIZE
+        assert self._fiemap_extent_cnt > 0
+        self._buf_size = self._fiemap_extent_cnt * _FIEMAP_EXTENT_SIZE
+        self._buf_size += _FIEMAP_SIZE
+
+        # Allocate a mutable buffer for the FIEMAP ioctl
+        self._buf = array.array('B', [0] * self._buf_size)
+
+        # Check if the FIEMAP ioctl is supported
+        self.block_is_mapped(0)
+
+    def _invoke_fiemap(self, block, count):
+        """
+        Invoke the FIEMAP ioctl for 'count' blocks of the file starting from
+        block number 'block'.
+
+        The full result of the operation is stored in 'self._buf' on exit.
+        Returns the unpacked 'struct fiemap' data structure in form of a python
+        list (just like 'struct.upack()').
+        """
+
+        if self.blocks_cnt != 0 and (block < 0 or block >= self.blocks_cnt):
+            raise Error("bad block number %d, should be within [0, %d]"
+                        % (block, self.blocks_cnt))
+
+        # Initialize the 'struct fiemap' part of the buffer. We use the
+        # '_FIEMAP_FLAG_SYNC' flag in order to make sure the file is
+        # synchronized. The reason for this is that early FIEMAP
+        # implementations had many bugs related to cached dirty data, and
+        # synchronizing the file is a necessary work-around.
+        struct.pack_into(_FIEMAP_FORMAT, self._buf, 0, block * self.block_size,
+                         count * self.block_size, _FIEMAP_FLAG_SYNC, 0,
+                         self._fiemap_extent_cnt, 0)
+
+        try:
+            fcntl.ioctl(self._f_image, _FIEMAP_IOCTL, self._buf, 1)
+        except IOError as err:
+            # Note, the FIEMAP ioctl is supported by the Linux kernel starting
+            # from version 2.6.28 (year 2008).
+            if err.errno == os.errno.EOPNOTSUPP:
+                errstr = "FilemapFiemap: the FIEMAP ioctl is not supported " \
+                         "by the file-system"
+                self._log.debug(errstr)
+                raise ErrorNotSupp(errstr)
+            if err.errno == os.errno.ENOTTY:
+                errstr = "FilemapFiemap: the FIEMAP ioctl is not supported " \
+                         "by the kernel"
+                self._log.debug(errstr)
+                raise ErrorNotSupp(errstr)
+            raise Error("the FIEMAP ioctl failed for '%s': %s"
+                        % (self._image_path, err))
+
+        return struct.unpack(_FIEMAP_FORMAT, self._buf[:_FIEMAP_SIZE])
+
+    def block_is_mapped(self, block):
+        """Refer the '_FilemapBase' class for the documentation."""
+        struct_fiemap = self._invoke_fiemap(block, 1)
+
+        # The 3rd element of 'struct_fiemap' is the 'fm_mapped_extents' field.
+        # If it contains zero, the block is not mapped, otherwise it is
+        # mapped.
+        result = bool(struct_fiemap[3])
+        self._log.debug("FilemapFiemap: block_is_mapped(%d) returns %s"
+                        % (block, result))
+        return result
+
+    def block_is_unmapped(self, block):
+        """Refer the '_FilemapBase' class for the documentation."""
+        return not self.block_is_mapped(block)
+
+    def _unpack_fiemap_extent(self, index):
+        """
+        Unpack a 'struct fiemap_extent' structure object number 'index' from
+        the internal 'self._buf' buffer.
+        """
+
+        offset = _FIEMAP_SIZE + _FIEMAP_EXTENT_SIZE * index
+        return struct.unpack(_FIEMAP_EXTENT_FORMAT,
+                             self._buf[offset : offset + _FIEMAP_EXTENT_SIZE])
+
+    def _do_get_mapped_ranges(self, start, count):
+        """
+        Implements most the functionality for the  'get_mapped_ranges()'
+        generator: invokes the FIEMAP ioctl, walks through the mapped extents
+        and yields mapped block ranges. However, the ranges may be consecutive
+        (e.g., (1, 100), (100, 200)) and 'get_mapped_ranges()' simply merges
+        them.
+        """
+
+        block = start
+        while block < start + count:
+            struct_fiemap = self._invoke_fiemap(block, count)
+
+            mapped_extents = struct_fiemap[3]
+            if mapped_extents == 0:
+                # No more mapped blocks
+                return
+
+            extent = 0
+            while extent < mapped_extents:
+                fiemap_extent = self._unpack_fiemap_extent(extent)
+
+                # Start of the extent
+                extent_start = fiemap_extent[0]
+                # Starting block number of the extent
+                extent_block = extent_start / self.block_size
+                # Length of the extent
+                extent_len = fiemap_extent[2]
+                # Count of blocks in the extent
+                extent_count = extent_len / self.block_size
+
+                # Extent length and offset have to be block-aligned
+                assert extent_start % self.block_size == 0
+                assert extent_len % self.block_size == 0
+
+                if extent_block > start + count - 1:
+                    return
+
+                first = max(extent_block, block)
+                last = min(extent_block + extent_count, start + count) - 1
+                yield (first, last)
+
+                extent += 1
+
+            block = extent_block + extent_count
+
+    def get_mapped_ranges(self, start, count):
+        """Refer the '_FilemapBase' class for the documentation."""
+        self._log.debug("FilemapFiemap: get_mapped_ranges(%d,  %d(%d))"
+                        % (start, count, start + count - 1))
+        iterator = self._do_get_mapped_ranges(start, count)
+        first_prev, last_prev = iterator.next()
+
+        for first, last in iterator:
+            if last_prev == first - 1:
+                last_prev = last
+            else:
+                self._log.debug("FilemapFiemap: yielding range (%d, %d)"
+                                % (first_prev, last_prev))
+                yield (first_prev, last_prev)
+                first_prev, last_prev = first, last
+
+        self._log.debug("FilemapFiemap: yielding range (%d, %d)"
+                        % (first_prev, last_prev))
+        yield (first_prev, last_prev)
+
+    def get_unmapped_ranges(self, start, count):
+        """Refer the '_FilemapBase' class for the documentation."""
+        self._log.debug("FilemapFiemap: get_unmapped_ranges(%d,  %d(%d))"
+                        % (start, count, start + count - 1))
+        hole_first = start
+        for first, last in self._do_get_mapped_ranges(start, count):
+            if first > hole_first:
+                self._log.debug("FilemapFiemap: yielding range (%d, %d)"
+                                % (hole_first, first - 1))
+                yield (hole_first, first - 1)
+
+            hole_first = last + 1
+
+        if hole_first < start + count:
+            self._log.debug("FilemapFiemap: yielding range (%d, %d)"
+                            % (hole_first, start + count - 1))
+            yield (hole_first, start + count - 1)
+
+def filemap(image, log=None):
+    """
+    Create and return an instance of a Filemap class - 'FilemapFiemap' or
+    'FilemapSeek', depending on what the system we run on supports. If the
+    FIEMAP ioctl is supported, an instance of the 'FilemapFiemap' class is
+    returned. Otherwise, if 'SEEK_HOLE' is supported an instance of the
+    'FilemapSeek' class is returned. If none of these are supported, the
+    function generates an 'Error' type exception.
+    """
+
+    try:
+        return FilemapFiemap(image, log)
+    except ErrorNotSupp:
+        return FilemapSeek(image, log)