Re: LVM and RO device/partition(s)

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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).


Hi

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...

Regards

Zdenek

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