Description of problem:

For the 5.7 release, we documented the snapshot_autoextend feature as follows:

---
As of the Red Hat Enterprise Linux 5.7 release, there are two new
features related to snapshots. First, in addition to the snapshot itself
being invalidated when full, any mounted file systems on that
snapshot device are forcibly unmounted, avoiding the inevitable
file system errors upon access to the mount point. Second, you can
specify the <literal>snapshot_autoextend_threshold</literal> option
in the <filename>lvm.conf</filename> file.
This option allows automatic extension of a snapshot whenever the remaining
snapshot space drops below the threshold you set. This feature requires
that there be unallocated space in the volume group.

Information on setting
snapshot_autoextend_threshold and snapshot_autoextend_percent
is provided in the lvm.conf file itself.  

---
We did not document this feature for RHEL 6, however, even though the lvm.conf file for RHEL 6 that we included in the document notes the parameters for this feature.

I asked Peter Rockai whether this feature was in RHEL 6.3 and whether it was also in RHEL 6.2 and he responded:

<mornfall> slevine: The gist is that you are right on all counts.
<mornfall> slevine: The code is definitely upstream for a while and will be in 6.3, most likely is also in 6.2.
<slevine> I'll add the info I put into 5.7 to 6.3 and pass it by you for review, if that's ok.
<mornfall> Yes, works for me, thanks.

This bug is to track the documentation of this feature.