Re: [linux-lvm] Snapshot resizing bug (LVM1)

["Heinz J . Mauelshagen" <mauelshagen@sistina.com>]

Dale,

thanks for finding this bug.
Obviously people don't resize populated snapshots very often or we'ld
seen this one much earlier ;)
Your fix is in LVM_BRANCH_1-0 for everybody to test.

We plan to revert CVS and will announce the change seperately.

Regards,
Heinz    -- The LVM Guy --


On Wed, Feb 05, 2003 at 01:07:01PM -0500, Dale J. Stephenson wrote:
> I've discovered a problem with using lvreduce/lvextend on LVM.  The 
> resized snapshot will have a new exception table and hash table 
> allocated for it.  But lvm_hash_link will be called for these in a loop 
> that depends on the lv_remap_ptr counter passed down from userspace -- 
> which will always be zero.  The result is that existing COW on the 
> snapshot are ignored, and the contents of the snapshot can magically 
> change to reflect the current state of the source volume.  Reboot (or 
> deactivating and reactivating the volume group) should solve the 
> problem, although it may be possible in the meantime to store a new COW 
> exception for a chunk that already has one.
> 
> The fix is simple:
> 
> --- lvm.c.orig  Tue Feb  4 18:36:58 2003
> +++ lvm.c       Tue Feb  4 18:43:26 2003
> @@ -2792,7 +2792,7 @@
>                  old_lv->lv_snapshot_hash_mask =
>                      new_lv->lv_snapshot_hash_mask;
> 
> -               for (e = 0; e < new_lv->lv_remap_ptr; e++)
> +               for (e = 0; e < old_lv->lv_remap_ptr; e++)
>                          lvm_hash_link(new_lv->lv_block_exception + e,
>                                        new_lv->lv_block_exception[e].
>                                        rdev_org,
> 
> As a side note, why not revert the main LVM cvs tree back to LVM 1.0.6? 
>   1.1 is dead.
> 
> Dale J. Stephenson
> dalestephenson@mac.com
> 
> 
> _______________________________________________
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> read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/

*** Software bugs are stupid.
    Nevertheless it needs not so stupid people to solve them ***

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Heinz Mauelshagen                                 Sistina Software Inc.
Senior Consultant/Developer                       Am Sonnenhang 11
                                                  56242 Marienrachdorf
                                                  Germany
Mauelshagen@Sistina.com                           +49 2626 141200
                                                       FAX 924446
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