Messages in this thread | | | Date | Tue, 19 Jul 2011 13:46:28 -0700 | From | "Linda A. Walsh" <> | Subject | Re: [linux-lvm] mount's (&udev's) dirty little naming problem |
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Luca Berra wrote: > On Tue, Jul 19, 2011 at 12:57:21AM -0700, Linda A. Walsh wrote: >> (sorry for the length of this, in advance, but I've tried to give >> this some though...(maybe not enough/maybe too much!) ;-) ) >> >> Luca Berra wrote: >> > On Mon, Jul 11, 2011 at 03:16:31AM +0100, Alasdair G Kergon wrote: >> >> The canonical name to use is /dev/<vgname>/<lvname>. ... >> >> >> >> [~Other forms - dm-N and /dev/mapper/X-Y are internal and ... >> >> there'll probably be some further changes to workaround other >> >> arbitrary udev restrictions...~] >> >> >> >> Different versions of df and mount haven't always retained this >> >> preferred form for their output. >> >> >> > note that on a freshly installed rhel 6.1 i have this in fstab >> > >> > /dev/mapper/vg_candela--lv_root / ext4 .... >> >> --- >> >> Why are there two dashes between the VG&LG? > woops, typo, sorry for that it is : > /dev/mapper/vg_candela-lv_root / ext4 defaults 1 1 > > L. ------ That's consistent with current behavior -- the problem is in the current name mangling (i,e. mounts by "/dev/VG/LV" get xlated into "/dev/mapper/<mangled-VG>-<mangled-LV>", where at least one manglement is xlating "-" into "--". But I've already been told that future manglements may be added due to limitations in udev.
For non LV devs, it would be like having '/dev/sdc2' xlated into '(hd2,<rand>)' (where <rand> = some not always consistent integer) which, of course would be silly! ( ;-) ), or xlating LABEL="MyDisk-Label" => '/dev'disk/by-label/MYDISK--LABEL' (with 'My-Label' being 'canonicalized', for some definition of thereof, into some other value), vs. now, it's given the real devname (/dev/sdc<x>) (which is FINE with me...; it's the real HW name that the kernel uses, whereas 'label=xxx was a syntax I was encouraged to use as part of the suse boot system, as 'everything works with labels' (well, lets not speak about lilo, or booting from an HD w/o a ram disk, as we'll just drop support for those options...*cough*)....
As noted, the current behavior isn't giving/using either the 'real devname' /dev/dm-[x], NOR the user name, but a mangled name making it the worst of all worlds, as there is no easy way to find out the LV and VG of the device mounted on a given mount point.
To get around this == and tell me if I'm wrong, I have to use lvm, to output a list of all VG,LV groups.
Then using a [perl] script (I suppose BASH's Associative arrays might work too, but familiarity points toward perl at this point), I can build up an Assoc array to map devno's -> VG,LV, then use the devno of the mountpoint as an index into that.
That level of complexity is so completely LAME just to find out the name I used to mount a FS on some mount point!....
If there is an easier way, please, hit me with a clue stick!
-l
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