[parted-devel] [BUG] failing ioctl when informing the kernel about new partitions

[Bryn M. Reeves]

Petr Uzel wrote:
> The problem is described in
> https://bugzilla.redhat.com/show_bug.cgi?id=441244
> with detailed instructions how to reproduce it and a patch.
> 
> I can confirm that the patch fixes the problem for me, but it
> did not get it to parted. As Bryn wrote in comment #2, it needs some
> discussion because of the possible interference with bootloaders (I'm
> going to test what might happen with grub/lilo installed to extended
> partition in this case).

Hi Petr,

It's a slightly awkward problem; what I'd like to see is that parted's 
manipulation of the kernel partition tables leads to the exact same 
result as the kernel's own partition table code, by whatever mechanism 
parted uses.

Unfortunately, as you'll see in the comments in Red Hat bug 441244, 
this is impossible with the BLKPG API (the kernel enforces stricter 
constraints on userspace than on its own partition detection code: 
specifically that partitions may never overlap. I don't necessarily 
think that's a "Bad Thing" btw!).

Right now, I don't have a really good answer for this. The fix that 
was applied in RHEL allows this case to work but may mean that, after 
reloading the partition table in this way, bootloaders cannot access 
the EBR until after the next reboot. I have never had a report of this 
causing problems but it is a side effect of the (desired) reload fix.

I am inclined to think that it may be better to fix the BLKRRPART 
ioctl instead - if this allowed reloading a busy partition table iff 
there are no conflicts between the old/new state then all this munging 
via BLKPG would not be necessary. As it stands, if even one partition 
is busy the kernel will not re-read the partition table (even if you 
just added a new partition in previously unused space - an operation 
that is clearly safe). At least, this was the state the last time I 
tested - I'll get back and try this on a recent git to make sure.

If anyone else has ideas on this I would really love to hear them.

Regards,
Bryn.