[linux-lvm] LVM and RO device/partition(s)

Zdenek Kabelac zdenek.kabelac at gmail.com
Mon Mar 20 13:57:49 UTC 2023

Dne 19. 03. 23 v 11:27 Pascal napsal(a):
> hi,
> the bio_check_ro function of the blk-core.c source file of the Linux kernel 
> refers to LVM :
> https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/block/blk-core.c?h=v6.2.7#n500 <https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/block/blk-core.c?h=v6.2.7#n500>
> how does LVM currently behave when faced with a device marked as readonly ?
> does it automatically switch itself in readonly mode?
> according to some tests carried out in a virtual machine, it seems that it 
> doesn't and that LVM modifies the disk/partition(s) even though they are all 
> readonly (chmod 444 && blockdev --setro).


There is no extra logic around RO devices in lvm2.  When lvm2 succeeds opening 
device in write mode, it'll use it for writing.

Also note - when you 'activate' a LV in read-write mode - someone opens such 
LV/device and you later on 'lvchange' such active LV to read-only mode - all 
writers will keep writing to such device.

It's not quite clear which kind of problem you are actually hitting - so maybe 
adding some more descriptive  environment +  logs  might give more info about 
your individual case.

Note: root admin typically can overwrite any 'mild' protections...



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