Re: [Libguestfs] [RFC] Inconsistent output of guestfs_list_filesystems
On Tue, Jan 23, 2018 at 12:44:10AM +0200, Mykola Ivanets wrote:
Before I rush to change something I request your comments on the
subject.
Let me know what do you think and if it does make sense.
The issue: guesfs_list_filesystems is inconsistent in its output.
The concept of guestfs_list_filesystem is that it returns a list
something like the list that running ‘df’ inside a traditional Unix
would return, ie. a list of mounted filesystems backed by real
devices, plus swap.
That's not an exact definition. A better way to understand it might
be to look at how it is is used (ie. ‘git grep list[-_]filesystems’).
For, example, it filters out partitioned physical devices but
doesn't do the same for MD devices.
Yes, this is a bug. I agree that the approach in your patches
(ie. filtering out explicitly partitioned devices) is better than the
current ad-hoc approach of listing whole devices, then partitioned
devices, then trying to remove whole devices uses a complicated
StringSet operation.
More over, according to its name and API documentation
guestfs_list_filesystem should return something which potentially
can be mounted (SWAP is an exclusion and it is stated in API doc).
It is the reason partitioned physical devices are filtered out: they
are not mountable even in theory (they don't contain filesystem if
they contain partition(s)).
Yes.
Another example of non-mountable block device is extended MSDOS
partition.
Do we return extended partitions? I thought not ..
Also nothing stops you from creating partition table and partitions
on logical volume (yes, it is probably uncommon but
nevertheless). In this case such partitions are ignored completely.
This is a bit of a corner case that we probably shouldn't spend too
much time on. Most ordinary Linux guests would also ignore these
(they probably indicate nested VMs).
Yet another example is Windows dynamic disks aka LDM:
guestfs_list_filesystems returns both ldm_vol_ and ldm_part_ but
strongly speaking only volumes should be considered as mountables.
I think this is a bug too.
And last example is again with Windows dynamic disks and their
physical counterparts: guestfs_list_filesystems filters out disks
with MBR type byte 0x42 but what about GPT?
Again, likely to be a bug.
More comments in the patches ...
Rich.
--
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