aliasing (or renaming) kern.geom.debugflags

Poul-Henning Kamp phk at
Sat Oct 8 08:18:56 UTC 2011

In message <alpine.BSF.2.00.1110071734140.4137 at>, Warren Block write

>Since we're talking about this, could you review the usage in the 
>gmirror section of the Handbook GEOM chapter:
>Seems like that is a valid non-debugging use, to allow the last block to 
>be written.

gmirror and this procedure has several problems:

1. It steals the last sector on the disk.  If that sector contained data
   you lost them, with no notice.  Most often it will not, particularly
   on a freshly installed system, but it is still a bad thing.

2. The paritioning is not fixed up to record the stealing of this sector.
   I wouldn't be surprised if this could cause confusion down the road.

3. In this case, writing only happens to a single sector, which we assume
   is not going to be written by anybody else, so apart from #1 and #2
   debugflags=16 does not cause any additional damage.

This is the kind of usage that makes me sad I ever added that option.

Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.

More information about the freebsd-current mailing list