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

[Colin Watson]

On Sun, Sep 06, 2015 at 10:56:08PM +0000, Carlos Checo wrote:
> Hardware and software are two separate things.

I'm aware of that (and could you have said this in any more patronising
a way?).  However, it does not affect the explanation I gave in the mail
you're replying to.

> The disk is "mounted" entirely it's just that the disks says it has
> two, one or more partitions.  The disk's description is read when
> plugged. When you mount you're using the software part not the
> hardware nature of the disk.

The blockdev command is a piece of software.  It changes a piece of data
stored by the kernel (which is also a piece of software) about the disk.
When you attempt to write to a disk (hardware), it goes through the
kernel's block device layer (software); the block device layer may
refuse the write on the grounds that its policy for that block device is
set to read-only.

-- 
Colin Watson                                       [cjwatson at ubuntu.com]