Change in vdsm[master]: Added utility to ensure that files written to the file syste...
asegurap at redhat.com
asegurap at redhat.com
Sat Sep 1 15:05:46 UTC 2012
Antoni Segura Puimedon has uploaded a new change for review.
Change subject: Added utility to ensure that files written to the file system happen atomically.
......................................................................
Added utility to ensure that files written to the file system happen atomically.
The only way in python to make a file be written in an atomic way is to take
advantage of the fact that in POSIX filesystems the rename operation is atomic.
Thus, we write the context to a temporary file on the same filesystem, sync on
the file descriptor and finally do the atomic file rename to the original file
we wanted to write.
For more info:
http://stackoverflow.com/questions/2333872/atomic-writing-to-file-with-python
http://stackoverflow.com/questions/7433057/is-rename-without-fsync-safe
Change-Id: Ibecd61d6746231a5a8cb17bad9a3302b01454f27
Signed-off-by: Antoni S. Puimedon <asegurap at redhat.com>
---
M vdsm/configNetwork.py
M vdsm/utils.py
2 files changed, 17 insertions(+), 1 deletion(-)
git pull ssh://gerrit.ovirt.org:29418/vdsm refs/changes/56/7656/1
diff --git a/vdsm/configNetwork.py b/vdsm/configNetwork.py
index 58117f8..b943574 100755
--- a/vdsm/configNetwork.py
+++ b/vdsm/configNetwork.py
@@ -369,7 +369,8 @@
'''Backs up the previous contents of the file referenced by fileName
writes the new configuration and sets the specified access mode.'''
self._backup(fileName)
- open(fileName, 'w').write(configuration)
+ with utils.atomicWrite(fileName) as f:
+ f.write(configuration)
os.chmod(fileName, 0664)
try:
selinux.restorecon(fileName)
diff --git a/vdsm/utils.py b/vdsm/utils.py
index 5e2d4e5..bb8a842 100644
--- a/vdsm/utils.py
+++ b/vdsm/utils.py
@@ -36,6 +36,7 @@
import fcntl
import functools
import stat
+from contextlib import contextmanager
import ethtool
@@ -829,3 +830,17 @@
def __unicode__(self):
return unicode(self.cmd)
+
+ at contextmanager
+def atomicWrite(file):
+ '''Context manager that makes the write happen to a temporary file and if
+ and only it is successful, overwrites the original file. It creates the
+ temporary file in the same directory of the destination file, as rename is
+ only atomic within the same filesystem.'''
+ tempFile = file+'vdsm_temp'
+ f = open(tempFile, 'w')
+ yield f
+ f.flush()
+ os.fsync(f.fileno())
+ f.close()
+ os.rename(tempFile, file)
--
To view, visit http://gerrit.ovirt.org/7656
To unsubscribe, visit http://gerrit.ovirt.org/settings
Gerrit-MessageType: newchange
Gerrit-Change-Id: Ibecd61d6746231a5a8cb17bad9a3302b01454f27
Gerrit-PatchSet: 1
Gerrit-Project: vdsm
Gerrit-Branch: master
Gerrit-Owner: Antoni Segura Puimedon <asegurap at redhat.com>
More information about the vdsm-patches
mailing list