Is it possible to mount an entire disk device read only?

[Colin Watson]

On Mon, Sep 07, 2015 at 05:06:56PM +0000, Carlos Checo wrote:
> Well what I mean is that by design is most probably not possible with
> actual software. If such action would be made then you would see partitions
> as separately folders. ( I guess )

Huh?  Whether device nodes are laid out as adjacent files or in
subdirectories has no relation at all to whether the read-only policy on
a disk affects the partitions it contains, or anything like that.
Device node layout is cosmetic as far as the kernel is concerned.

The kernel knows that partitions are "part of" a disk device, and it in
fact has a function to set an entire disk as read-only (set_disk_ro),
but that isn't currently exposed to userspace except for some special
purposes such as MD.  A similar function, set_device_ro, operates on
individual block devices, is exposed to userspace, and is the function
ultimately called by "blockdev --setro".

-- 
Colin Watson                                       [cjwatson at ubuntu.com]