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core: do not truncate qubes.xml during save()

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Save the next one in temporary file, then move over to destination file.
This way when writing the file to disk fails (e.g. out of disk space),
user still have old file version intact.
This commit is contained in:
Marek Marczykowski-Górecki 2013-12-02 03:32:33 +01:00
parent 93b7924bc6
commit bc92c20d67
1 changed files with 12 additions and 5 deletions
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17
core/qubes.py
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@ -28,6 +28,8 @@ import xml.parsers.expat
import fcntl
import time
import warnings
import tempfile
import grp
# Do not use XenAPI or create/read any VM files
# This is for testing only!
@ -527,11 +529,16 @@ class QubesVmCollection(dict):
try:
# We need to manually truncate the file, as we open the
# file as "r+" in the lock_db_for_writing() function
self.qubes_store_file.seek (0, os.SEEK_SET)
self.qubes_store_file.truncate()
tree.write(self.qubes_store_file, encoding="UTF-8", pretty_print=True)
new_store_file = tempfile.NamedTemporaryFile(prefix=self.qubes_store_filename, delete=False)
# XXX: do not get lock on the new file, as in all use cases
# unlock_db() is the next operation after save()
tree.write(new_store_file, encoding="UTF-8", pretty_print=True)
new_store_file.flush()
os.chmod(new_store_file.name, 0660)
os.chown(new_store_file.name, -1, grp.getgrnam('qubes').gr_gid)
os.rename(new_store_file.name, self.qubes_store_filename)
self.qubes_store_file.close()
self.qubes_store_file = new_store_file
except EnvironmentError as err:
print("{0}: export error: {1}".format(
os.path.basename(sys.argv[0]), err))