From 4138d39f9964173249db1a4e9afe1d06846b8fc7 Mon Sep 17 00:00:00 2001
From: Iustin Pop <iustin@google.com>
Date: Fri, 22 Oct 2010 14:29:47 +0200
Subject: [PATCH] Add a "safe" file wrapper over WriteFile
Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Michael Hanselmann <hansmi@google.com>
---
lib/utils.py | 25 +++++++++++++++++++++++++
test/ganeti.utils_unittest.py | 15 +++++++++++++++
2 files changed, 40 insertions(+)
diff --git a/lib/utils.py b/lib/utils.py
index aa84cb1f8..bdd86105c 100644
--- a/lib/utils.py
+++ b/lib/utils.py
@@ -1912,6 +1912,31 @@ def VerifyFileID(fi_disk, fi_ours):
return (d1, i1) == (d2, i2) and m1 <= m2
+def SafeWriteFile(file_name, file_id, **kwargs):
+ """Wraper over L{WriteFile} that locks the target file.
+
+ By keeping the target file locked during WriteFile, we ensure that
+ cooperating writers will safely serialise access to the file.
+
+ @type file_name: str
+ @param file_name: the target filename
+ @type file_id: tuple
+ @param file_id: a result from L{GetFileID}
+
+ """
+ fd = os.open(file_name, os.O_RDONLY | os.O_CREAT)
+ try:
+ LockFile(fd)
+ if file_id is not None:
+ disk_id = GetFileID(fd=fd)
+ if not VerifyFileID(disk_id, file_id):
+ raise errors.LockError("Cannot overwrite file %s, it has been modified"
+ " since last written" % file_name)
+ return WriteFile(file_name, **kwargs)
+ finally:
+ os.close(fd)
+
+
def ReadOneLineFile(file_name, strict=False):
"""Return the first non-empty line from a file.
diff --git a/test/ganeti.utils_unittest.py b/test/ganeti.utils_unittest.py
index 7fc93db1f..2c46afcb1 100755
--- a/test/ganeti.utils_unittest.py
+++ b/test/ganeti.utils_unittest.py
@@ -2374,6 +2374,21 @@ class TestFileID(testutils.GanetiTestCase):
finally:
os.close(fd)
+ def testWriteFile(self):
+ name = self._CreateTempFile()
+ oldi = utils.GetFileID(path=name)
+ mtime = oldi[2]
+ os.utime(name, (mtime + 10, mtime + 10))
+ self.assertRaises(errors.LockError, utils.SafeWriteFile, name,
+ oldi, data="")
+ os.utime(name, (mtime - 10, mtime - 10))
+ utils.SafeWriteFile(name, oldi, data="")
+ oldi = utils.GetFileID(path=name)
+ mtime = oldi[2]
+ os.utime(name, (mtime + 10, mtime + 10))
+ # this doesn't raise, since we passed None
+ utils.SafeWriteFile(name, None, data="")
+
if __name__ == '__main__':
testutils.GanetiTestProgram()
--
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