Bug 216898

Summary: mkfs.gfs2 needs to zero the first 16 blocks of file system
Product: Red Hat Enterprise Linux 5 Reporter: Robert Peterson <rpeterso>
Component: gfs2-utilsAssignee: Robert Peterson <rpeterso>
Status: CLOSED CURRENTRELEASE QA Contact: GFS Bugs <gfs-bugs>
Severity: medium Docs Contact:
Priority: medium    
Version: 5.1CC: kanderso, rkenna
Target Milestone: ---   
Target Release: ---   
Hardware: All   
OS: Linux   
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Fixed In Version: RC Doc Type: Bug Fix
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Clone Of: Environment:
Last Closed: 2007-02-08 00:49:33 UTC Type: ---
Regression: --- Mount Type: ---
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Description Flags
patch to fix the problem none

Description Robert Peterson 2006-11-22 16:20:40 UTC 
Description of problem:
If you run mkfs.gfs2 on an existing file system, the first 16 blocks
of the file system are not being zeroed, and they should be.
If we don't, the leftover data in the new file system may be
misinterpreted as what it was prior to mkfs.gfs2.

For example, vfat and xfs both store their superblock at block 0.
If we don't zero it out, someone could try to mount the gfs2 
file system as the old type which will most likely panic the kernel.
Worse yet, someone could run mkfs.gfs2 on a raw device that used to 
be part of an lvm volume, and they might in theory confuse lvm.

Version-Release number of selected component (if applicable):
RHEL5

How reproducible:
Always

Steps to Reproduce:
1. mkfs.vfat /dev/bobs_vg/lvol7
2. mkfs.gfs2 -t bob_cluster2:lv7 -p lock_dlm -j 2 /dev/bobs_vg/lvol7
3. mkfs.gfs2 -t bob_cluster2:lv7 -p lock_dlm -j 2 /dev/bobs_vg/lvol7
  
Actual results:
On the second call to mkfs.gfs2, it says:
This will destroy any data on /dev/bobs_vg/lvol7.
  It appears to contain a vfat filesystem.

Are you sure you want to proceed? [y/n] 

Expected results:
Should only be recognized as gfs2, not vfat:

This will destroy any data on /dev/bobs_vg/lvol7.
  It appears to contain a gfs2 filesystem.

Are you sure you want to proceed? [y/n] 

Additional info:
Problem is in libgfs2, structures.c, function build_sb.
The buffers for blocks 0 - 15 are not being updated.
Comment 1 Robert Peterson 2006-11-22 18:37:53 UTC 
Created attachment 141927 [details]
patch to fix the problem

Here's a patch to libgfs2/structures.c to fix the problem.
Comment 3 RHEL Program Management 2007-02-08 00:49:33 UTC 
A package has been built which should help the problem described in 
this bug report. This report is therefore being closed with a resolution 
of CURRENTRELEASE. You may reopen this bug report if the solution does 
not work for you.