root / snf-pithos-backend / pithos / backends / lib / hashfiler / context_file.py @ c9b996b7
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# Copyright 2011-2012 GRNET S.A. All rights reserved.
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#
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# Redistribution and use in source and binary forms, with or
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# without modification, are permitted provided that the following
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# conditions are met:
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#
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# 1. Redistributions of source code must retain the above
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# copyright notice, this list of conditions and the following
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# disclaimer.
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#
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# 2. Redistributions in binary form must reproduce the above
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# copyright notice, this list of conditions and the following
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# disclaimer in the documentation and/or other materials
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# provided with the distribution.
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#
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# THIS SOFTWARE IS PROVIDED BY GRNET S.A. ``AS IS'' AND ANY EXPRESS
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# OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
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# WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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# PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL GRNET S.A OR
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# CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
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# USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
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# AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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# LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
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# ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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# POSSIBILITY OF SUCH DAMAGE.
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#
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# The views and conclusions contained in the software and
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# documentation are those of the authors and should not be
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# interpreted as representing official policies, either expressed
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# or implied, of GRNET S.A.
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from os import SEEK_CUR, SEEK_SET, fsync, makedirs, rename |
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from os.path import dirname |
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from errno import ENOENT, ESPIPE |
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_zeros = ''
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fsync # get used
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def zeros(nr): |
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global _zeros
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size = len(_zeros)
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if nr == size:
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return _zeros
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if nr > size:
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_zeros += '\0' * (nr - size)
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return _zeros
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if nr < size:
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_zeros = _zeros[:nr] |
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return _zeros
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def file_sync_write_chunks(openfile, chunksize, offset, chunks, size=None): |
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"""Write given chunks to the given buffered file object.
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Writes never span across chunk boundaries.
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If size is given stop after or pad until size bytes have been written.
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"""
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fwrite = openfile.write |
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seek = openfile.seek |
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padding = 0
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try:
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seek(offset * chunksize) |
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except IOError as e: |
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if e.errno != ESPIPE:
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raise
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# substitute seeking in a non-seekable file (e.g. pipe)
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seek = None
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for x in xrange(offset): |
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fwrite(zeros(chunksize)) |
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cursize = offset * chunksize |
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for chunk in chunks: |
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if padding:
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if seek:
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seek(padding - 1, SEEK_CUR)
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fwrite("\x00")
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else:
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fwrite(buffer(zeros(chunksize), 0, padding)) |
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if size is not None and cursize + chunksize >= size: |
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chunk = chunk[:chunksize - (cursize - size)] |
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fwrite(chunk) |
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cursize += len(chunk)
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break
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fwrite(chunk) |
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padding = chunksize - len(chunk)
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padding = size - cursize if size is not None else 0 |
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if padding <= 0: |
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return
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q, r = divmod(padding, chunksize)
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for x in xrange(q): |
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fwrite(zeros(chunksize)) |
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fwrite(buffer(zeros(chunksize), 0, r)) |
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def file_sync_read_chunks(openfile, chunksize, nr, offset=0): |
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"""Read and yield groups of chunks from a buffered file object at offset.
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Reads never span accros chunksize boundaries.
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"""
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fread = openfile.read |
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remains = offset * chunksize |
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seek = openfile.seek |
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try:
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seek(remains) |
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except IOError as e: |
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if e.errno != ESPIPE:
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raise
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# substitute seeking in a non-seekable file (e.g. pipe)
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seek = None
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while 1: |
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s = fread(remains) |
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remains -= len(s)
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if remains <= 0: |
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break
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while nr:
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remains = chunksize |
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chunk = ''
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while 1: |
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s = fread(remains) |
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if not s: |
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if chunk:
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yield chunk
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return
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chunk += s |
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remains -= len(s)
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if remains <= 0: |
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break
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yield chunk
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nr -= 1
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class ContextFile(object): |
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def __init__(self, name, create=True, write=False, temp=''): |
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self.name = name
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self.fdesc = None |
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self._create = create
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self._write = write
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self._mode = 'rb+' if write else 'rb' |
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self._temp = temp
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self._rename = False |
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#self.dirty = 0
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def __enter__(self): |
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name = self.name
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try:
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fdesc = open(name, self._mode) |
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except IOError, e: |
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if not (self._create and e.errno == ENOENT): |
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raise
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# File does not exist. Create it,
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# optionally under a temporary filename.
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temp = self._temp
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self._rename = False |
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if temp:
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name += '_' + temp
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self._rename = name
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try:
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fdesc = open(name, 'w+') |
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except IOError as e: |
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if e.errno != ENOENT:
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raise
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# ENOENT means parent dirs do not exist.
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# Create them.
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makedirs(dirname(name)) |
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fdesc = open(name, 'w+') |
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self.fdesc = fdesc
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return self |
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def __exit__(self, exc, arg, trace): |
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fdesc = self.fdesc
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if fdesc is not None: |
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#if self.dirty:
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# fsync(fdesc.fileno())
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fdesc.close() |
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tempname = self._rename
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if tempname:
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# Temporary file needs to be moved into proper place
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# This is usually an atomic filesystem operation.
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rename(tempname, self.name)
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return False # propagate exceptions |
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def seek(self, offset, whence=SEEK_SET): |
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return self.fdesc.seek(offset, whence) |
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def tell(self): |
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return self.fdesc.tell() |
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def truncate(self, size): |
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self.fdesc.truncate(size)
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def sync_write(self, data): |
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#self.dirty = 1
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self.fdesc.write(data)
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def sync_write_chunks(self, chunksize, offset, chunks, size=None): |
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#self.dirty = 1
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return file_sync_write_chunks(self.fdesc, |
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chunksize, offset, chunks, size) |
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def sync_read(self, size): |
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read = self.fdesc.read
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data = ''
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while 1: |
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s = read(size) |
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if not s: |
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break
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data += s |
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return data
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def sync_read_chunks(self, chunksize, nr, offset=0): |
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return file_sync_read_chunks(self.fdesc, chunksize, nr, offset) |