[Libvir] Re: parted/LVM for ET [Storage manager initial requirements and thoughts

Richard W.M. Jones rjones at redhat.com
Thu Jun 14 14:50:28 UTC 2007

Jim Meyering wrote:

Thanks for looking into this.

> In addition, there is the fact that Parted's partition-table (aka
> what it calls "label") support is currently tied to a 512-byte sector
> size for many label types.  BTW, do any of you know which are the
> partition types that matter the most to us?  MSDOS and GPT seem like
> the top priority ones, and I've fixed most parts of those two, but
> have only lightly tested the GPT changes.  Also, with >512-byte sector
> devices becoming more and more common (e.g., ipods, CDs, new-and-bigger
> disks), I wonder how important it is to make Parted work for them, now.
> Fixing Parted for the few most common partition types isn't a big deal,
> but fixing all of them would require more time and testing resources than
> I expect to have.  I plan to leave most of the others in their current,
> works-only-for-512-byte-sectors state.

 From the virt-manager/libvirt p.o.v. it seems to me the important 
operations are:

(1) Find attached drives.

(2) Find partitions available & their sizes.

(3) Allocate logical volumes.

(4) Find out how much free space is available on a partition, and carve 
out a file.

Correct me if I'm wrong (I usually am), but:

Nothing can do (1) except doing a brute force scan over /dev and looking 
for likely block devices (this is what vgscan does).

Parted can do (2), with several limitations including sector size.  It 
can't do (3) at all, but then neither can anything else except forking 
the LVM command line tools.

And (4) can be done by libvirtd using ordinary POSIX calls, so no 
external library support is needed, just some work to remote those 
operations (which is mostly done).


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