Issue 10760: tarfile doesn't handle sysfs well (original) (raw)

When I try to add a special file from sys, e.g.: /sys/class/scsi_host/host0/cmd_per_lun (which is reported of size 4096 but actually reading it will return only several bytes of a result), I get the following exception:

Traceback (most recent call last): File "/opt/xpyv/lib/python26.zip/tarfile.py", line 1975, in add self.addfile(tarinfo, f) File "/opt/xpyv/lib/python26.zip/tarfile.py", line 2004, in addfile copyfileobj(fileobj, self.fileobj, tarinfo.size) File "/opt/xpyv/lib/python26.zip/tarfile.py", line 287, in copyfileobj raise IOError("end of file reached") IOError: end of file reached

Notice what happens if I try to add the file with regular tar: root@buzaglo # tar cvzf /tmp/blat.tgz /sys/class/scsi_host/host0/cmd_per_lun tar: Removing leading `/' from member names /sys/class/scsi_host/host0/cmd_per_lun tar: /sys/class/scsi_host/host0/cmd_per_lun: File shrank by 4094 bytes; padding with zeros tar: Error exit delayed from previous errors

So it handles the issue by padding the rest of the file size with zeros.

I think this should be the behavior as well, instead of throwing an IOError.

Here's a test case that re-creates this issue. I chose to use mocks instead of sample files from sysfs so it would be simpler to run, it can be easily changed to use a file from sysfs.

The following code runs on Python2.7, requires the mock library

{code} from unittest import TestCase from tempfile import mkstemp from mock import patch, Mock from os import close, remove, write, stat from posix import stat_result from tarfile import TarFile

def fake_st_size_side_effect(*args, **kwargs): src, = args stats = stat(src) return stat_result((stats.st_mode, stats.st_ino, stats.st_dev, stats.st_nlink, stats.st_uid, stats.st_gid, stats.st_size + 10, stats.st_atime, stats.st_mtime, stats.st_ctime))

class Issue10760TestCase(TestCase): def setUp(self): fd, self.src = mkstemp() write(fd, '\x00' * 4) close(fd) fd, self.dst = mkstemp() close(fd)

def test(self):
    with patch("os.lstat") as lstat:
        lstat.side_effect = fake_st_size_side_effect
        tar_file = TarFile.open(self.dst, 'w:gz')
        tar_file.add(self.src)

{code}