Bug 489946

Summary: libvirt does not do safe replacement of guest/storage pool/network config files
Product: [Community] Virtualization Tools Reporter: Daniel BerrangĂ© <berrange>
Component: libvirtAssignee: Daniel Veillard <veillard>
Status: CLOSED CURRENTRELEASE QA Contact:
Severity: medium Docs Contact:
Priority: low    
Version: unspecifiedCC: berrange, clalance, crobinso, eblake, veillard, virt-maint, xen-maint
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Hardware: All   
OS: Linux   
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Fixed In Version: Doc Type: Bug Fix
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Last Closed: 2012-03-30 20:53:25 UTC Type: ---
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Description Daniel Berrangé 2009-03-12 16:32:41 UTC 
Description of problem:
When defining a new guest/storage pool/network config file, libvirt simply opens the config file, truncating existing content and then writes the new one. This is not safe against a wide variety of errors. If the write() or close() step fails, the user is potentially left with a zero length config file. If host crashes, the new config may not have been flushed to disk again leaving a zero length file, or corrupted file. It needs to implement a much more robust method for writing out new config files. 

cf this preso for guide on how to write safely http://www.flamingspork.com/talks/2007/06/eat_my_data.odp


Version-Release number of selected component (if applicable):
0.6.1

How reproducible:


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Comment 1 Bug Zapper 2009-06-09 12:10:47 UTC 
This bug appears to have been reported against 'rawhide' during the Fedora 11 development cycle.
Changing version to '11'.

More information and reason for this action is here:
http://fedoraproject.org/wiki/BugZappers/HouseKeeping
Comment 2 Eric Blake 2012-03-30 20:53:25 UTC 
Fixed in 0.9.7 with:
commit 559644ddd2fd7065220331d11197bf54f6484231
Author: Jiri Denemark <jdenemar>
Date:   Thu Oct 13 12:17:12 2011 +0200

    Introduce virFileRewrite for safe file rewrite
    
    When saving config files we just overwrite old content of the file. In
    case something fails during that process (e.g. disk gets full) we lose
    both old and new content. This patch makes the process more robust by
    writing the new content into a separate file and only if that succeeds
    the original file is atomically replaced with the new one.