[linux-lvm] [dm-devel] fixing mangled UUIDs

Discussion:

John Stoffel

2015-12-09 16:40:20 UTC

Alasdair> Have you tried '--manglename none' if you aren't using a
Alasdair> udev system that mangles names? (Also available via
Alasdair> environmnet variable - see man page.)

That seems to be working, using the default Debbian Jessie lvm tools:

dmsetup --manglename none status --target cache
data-home: 0 1153433600 cache 8 2443/32768 128 54020/819200 80721
350897 64427 66938 0 23882 1 1 writeback 2 migration_threshold 2048
smq 0 rw -
data-local: 0 702545920 cache 8 2443/32768 128 1078/819200 6268 85795
1492 2715 0 1057 0 1 writeback 2 migration_threshold 2048 smq 0 rw -

So now I can try to monitor my cache usage.

So the question still remains, what is the long term fix so I don't
have to deal with this breakage by default? Do I have bad UUIDS on my
volumes?

John

John Stoffel

2015-12-09 20:39:35 UTC

Permalink

Zdenek> Dne 9.12.2015 v 17:40 John Stoffel napsal(a):
Alasdair> Have you tried '--manglename none' if you aren't using a
Alasdair> udev system that mangles names? (Also available via
Alasdair> environmnet variable - see man page.)

Post by John Stoffel
dmsetup --manglename none status --target cache
data-home: 0 1153433600 cache 8 2443/32768 128 54020/819200 80721
350897 64427 66938 0 23882 1 1 writeback 2 migration_threshold 2048
smq 0 rw -
data-local: 0 702545920 cache 8 2443/32768 128 1078/819200 6268 85795
1492 2715 0 1057 0 1 writeback 2 migration_threshold 2048 smq 0 rw -
So now I can try to monitor my cache usage.
So the question still remains, what is the long term fix so I don't
have to deal with this breakage by default? Do I have bad UUIDS on my
volumes?

Zdenek> Yep

Zdenek> See supported charset:

Zdenek> --
Zdenek> Mangle any character not on a whitelist using mangling_mode when processing
Zdenek> device-mapper device names and UUIDs. The names and UUIDs are mangled on
Zdenek> input and unmangled on output where the mangling mode is one of: auto
Zdenek> (only do the mangling if not mangled yet, do nothing if already mangled, error
Zdenek> on mixed), hex (always do the mangling) and none (no mangling). Default mode
Zdenek> is auto. Character whitelist: 0-9, A-Z, a-z, #+-.:=@_. This whitelist is also
Zdenek> supported by udev. Any character not on a whitelist is replaced with its
Zdenek> hex value (two digits) prefixed by \x. Mangling mode could be also set
Zdenek> through DM_DEFAULT_NAME_MANGLING_MODE environment variable.
Zdenek> ---

Zdenek> Udev create symlinks from UUID - so they need to be using udev-supported
Zdenek> chars - and you '!' in UUID -> unsupported and needs mangling.

I'm happy to fix the UUIDs, the question is HOW. Ideally without
having to shutdown the system.

As I explained in my earlier email, I tried using 'lvchange -an
data/pete' to disable one of my LVs (after unmounting it) but then I
can't see it to manage it with dmsetup to fix the UUIDs.

John

Zdenek Kabelac

2015-12-10 09:05:21 UTC

Permalink

Post by John Stoffel
Alasdair> Have you tried '--manglename none' if you aren't using a
Alasdair> udev system that mangles names? (Also available via
Alasdair> environmnet variable - see man page.)

Zdenek> Yep
Zdenek> --
Zdenek> Mangle any character not on a whitelist using mangling_mode when processing
Zdenek> device-mapper device names and UUIDs. The names and UUIDs are mangled on
Zdenek> input and unmangled on output where the mangling mode is one of: auto
Zdenek> (only do the mangling if not mangled yet, do nothing if already mangled, error
Zdenek> on mixed), hex (always do the mangling) and none (no mangling). Default mode
Zdenek> supported by udev. Any character not on a whitelist is replaced with its
Zdenek> hex value (two digits) prefixed by \x. Mangling mode could be also set
Zdenek> through DM_DEFAULT_NAME_MANGLING_MODE environment variable.
Zdenek> ---
Zdenek> Udev create symlinks from UUID - so they need to be using udev-supported
Zdenek> chars - and you '!' in UUID -> unsupported and needs mangling.
I'm happy to fix the UUIDs, the question is HOW. Ideally without
having to shutdown the system.
As I explained in my earlier email, I tried using 'lvchange -an
data/pete' to disable one of my LVs (after unmounting it) but then I
can't see it to manage it with dmsetup to fix the UUIDs.

dmsetup remove unwanted-vg-lv-name

vgcfgbackup

vim and fix UUID (replace ! char) by hand

vgcfgrestore

Regard

Zdenek

John Stoffel

2015-12-10 15:15:41 UTC

Permalink

Post by John Stoffel

Zdenek> Yep
Zdenek> See supported charset:
Zdenek> --
Zdenek> Mangle any character not on a whitelist using mangling_mode when processing
Zdenek> device-mapper device names and UUIDs. The names and UUIDs are mangled on
Zdenek> input and unmangled on output where the mangling mode is one of: auto
Zdenek> (only do the mangling if not mangled yet, do nothing if already mangled, error
Zdenek> on mixed), hex (always do the mangling) and none (no mangling). Default mode
Zdenek> is auto. Character whitelist: 0-9, A-Z, a-z, #+-.:=@_. This whitelist is also
Zdenek> supported by udev. Any character not on a whitelist is replaced with its
Zdenek> hex value (two digits) prefixed by \x. Mangling mode could be also set
Zdenek> through DM_DEFAULT_NAME_MANGLING_MODE environment variable.
Zdenek> ---
Zdenek> Udev create symlinks from UUID - so they need to be using udev-supported
Zdenek> chars - and you '!' in UUID -> unsupported and needs mangling.

Post by John Stoffel
I'm happy to fix the UUIDs, the question is HOW. Ideally without
having to shutdown the system.
As I explained in my earlier email, I tried using 'lvchange -an
data/pete' to disable one of my LVs (after unmounting it) but then I
can't see it to manage it with dmsetup to fix the UUIDs.

Zdenek> dmsetup remove unwanted-vg-lv-name

Zdenek> vgcfgbackup

Zdenek> vim and fix UUID (replace ! char) by hand

Zdenek> vgcfgrestore

Awesome, but can I do this with the system live? Or do I need to boot
into a rescue CD to make this? Hidden assumptions are the killer
here.

Zdenek Kabelac

2015-12-10 20:59:55 UTC

Permalink

Post by John Stoffel
Alasdair> Have you tried '--manglename none' if you aren't using a
Alasdair> udev system that mangles names? (Also available via
Alasdair> environmnet variable - see man page.)

Post by John Stoffel

Zdenek> dmsetup remove unwanted-vg-lv-name
Zdenek> vgcfgbackup
Zdenek> vim and fix UUID (replace ! char) by hand
Zdenek> vgcfgrestore
Awesome, but can I do this with the system live? Or do I need to boot
into a rescue CD to make this? Hidden assumptions are the killer
here.

Yes - should be safe - as long as you will not try to modify more things in
parallel.

Anyway - this issue will need upstream fix.
But if you need something 'right now' - use the above sequence.

Regards

Zdenek