Re: [Libguestfs] [PATCH v2v] convert: Ignore /dev/mapper/osprober-* devices when trimming

On Tue, May 17, 2022 at 07:54:01AM +0200, Laszlo Ersek wrote: > On 05/16/22 17:46, Richard W.M. Jones wrote: >> These devices can be left around by either grub2 or the osprober tool. >> They are read-only mirrors of existing filesystems and it appears we >> can safely ignore them. >> >> Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=2003503 >> --- >> convert/convert.ml | 6 ++++++ >> 1 file changed, 6 insertions(+) >> >> diff --git a/convert/convert.ml b/convert/convert.ml >> index 87fca7252b..997f6b08bd 100644 >> --- a/convert/convert.ml >> +++ b/convert/convert.ml >> @@ -194,10 +194,16 @@ and do_fstrim g inspect = >> (* Get all filesystems. *) >> let fses = g#list_filesystems () in >> >> + (* Ignore unknown/swap devices. *) >> let fses = List.filter_map ( >> function (_, ("unknown"|"swap")) -> None | (dev, _) -> Some dev >> ) fses in >> >> + (* Ignore filesystems left around by osprober (RHBZ#2003503). *) >> + let fses = >> + List.filter (fun dev -> not (String.is_prefix dev "/dev/mapper/osprober-")) >> + fses in >> + >> (* Trim the filesystems. *) >> List.iter ( >> fun dev -> >> > > I've read up on os-prober: > > https://www.thegeekdiary.com/how-to-disable-os-prober-in-centos-rhel-7/ > https://github.com/campadrenalin/os-prober > http://joeyh.name/code/os-prober/ > > and it's *absolutely infuriating* that os-prober itself, or whatever > invokes os-prober, litters the system with block device nodes. In fact, > I don't even know how it is *possible* for a device node to be left > around under /dev/mapper -- I thought /dev/mapper/ would be re-populated > *from zero* every time the system boots? Do we have something in the > appliance perhaps that *creates* these files? As part of conversion we run “/sbin/grub2-mkconfig -o /boot/grub2/grub.cfg” which runs osprober and that leaves the block devices around. Later in conversion we list out all filesystems (ie. g#list_filesystems) and try to trim these, which is what was giving the warnings. This is only a workaround for the original bug which seems to be in grub/osprober. > I'm quite unhappy about ignoring these filesystems in "do_fstrim" > *only*. If guestfs_list_filesystems() returns them in the first place, > won't that cause confusion for other libguestfs applications or scripts? Quite possibly, but I was fixing the smallest possible thing to make the bug go away. > Do we expect the same filesystem to appear multiply in the > list-filesystems output? During conversion, list_filesystems output is [tidied up]: list_filesystems = [ "/dev/mapper/osprober-linux-rhel_bootp--73--199--22-root", "xfs"; "/dev/mapper/osprober-linux-sda1", "xfs"; "/dev/sda1", "xfs"; "/dev/sda3", "xfs"; "/dev/rhel_bootp-73-199-22/root", "xfs"; "/dev/rhel_bootp-73-199-22/swap", "swap"; "/dev/rhel_bootp-73-199-6/root", "xfs"; "/dev/rhel_bootp-73-199-6/swap", "swap" ] (/dev/mapper/osprober-linux-sda1 & /dev/sda1), and (/dev/mapper/osprober-linux-rhel_bootp--73--199--22-root & /dev/rhel_bootp-73-199-22/root) are both duplicates. It would be quite hard to deduplicate these however (unless you know some trick), since the /dev/mapper/osprober-* devices are just read-only device-mapper linear entries. There's nothing apart from the name that easily connects them to the partitions and LVs that they cover (particularly the LV).

> I think this is a serious bug in some component different from > libguestfs / virt-v2v. Without a doubt, it's a bug in grub2/osprober. > Hmmm... After reading your comment > <https://bugzilla.redhat.com/show_bug.cgi?id=2003503#c12>;, I think we > absolutely need to report a bug for grub2. I'll contact the rhboot team. > > I don't disagree that we have to work it around, but until we understand > the problem better, I don't feel safe about filtering these nodes out > only in virt-v2v's trimming function. Sure, I'll leave this one for now. Rich.