[Fedora-livecd-list] possible bug alert: device-mapper: snapshots: invalid or corrupt snapshot

[Douglas McClendon]

Douglas McClendon wrote:
> I've been running into a bug, but can't yet rule out my own code, even 
> though I really really don't think I could have caused it.

...

> Though if anybody is curious enough to remove the dd '2> /dev/null' and 
> see if they get the 0 records in/out result, and hopefully can explain 
> why in the world that is happening...  I'd be greatful...

There is just something about hitting that send button, that makes you 
think of something you should have thought of before hitting it...

I never noticed the subtle difference between doing

dd if=/dev/zero

and

dd if=/dev/null

That completely explains that part of all my confusion (the dd stuff). 
But it doesn't explain the bug that I can trip a fraction of the time 
when rerunning the same qemu command against the same iso 10 times over.

I.e. what started that confusion, was me knowing enough in the emergency 
shell to try manually rerunning the dmsetup create command, watching the 
same 'invalid or corrupt snapshot error', then manually creating a new 
overlay sparse file (but with /dev/zero because that is my habbit), and 
then bizarrely noticing the 1024 byte difference in size between the two 
files.  Then being more perplexed when I could run the dmsetup create 
command against the new file and have it work, instead of fail.

-dmc