Re: [PATCH] mmc: boot partition ro lock support

[Chris Ball <cjb@laptop.org>]

Hi Ulf,

On Mon, Oct 24 2011, Ulf Hansson wrote:
> The kernel could very much be used in manufacturing environment as
> well. Don't know if and how we should consider this.
>
> Do you think a change to an ioctl is a better alternative than sysfs?
> Then let's change to that!

Ah, we're not proposing a new ioctl for this -- we're proposing that the
perm-r/o command could be sent from a userspace binary that *uses* the
arbitrary command ioctl that we already have.

The arbitrary command ioctl is drivers/mmc/card/block.c:mmc_blk_ioctl_cmd().

Please could you send a version of the patch that supports power-on r/o
but not perm r/o, and perhaps also post userspace code for submitting
the perm r/o command through the ioctl interface?  (Perhaps this code
should eventually be submitted to a disk management tool..)

Also, it looks like it's possible to set read-only for the whole device,
as well as for boot partitions.  Could you update the patch to allow
setting power-on r/o for the entire card, not just the boot partitions?

> Enable boot partitions to be power and permanently read-only locked via
> a sysfs entry. There will be one sysfs entry for the main mmc device:
> 
> /sys/block/mmcblkX/boot_partition_ro_lock

I don't follow why this node is necessary, instead of just having the
nodes in the mmcblkXbootY/ directories.  Could you explain?

> and one for each boot partition:
> 
> /sys/block/mmcblkXbootY/ro_lock
>
> The boot partitions are power or permanently locked by writing "pwr_ro"
> or "perm_ro" to one of the files.

Now that we're only having one type of r/o lock, let's do:

  echo 1 > /sys/block/mmcblkXbootY/ro_lock_until_next_power_on

to lock just a boot partition, and:

  echo 1 > /sys/block/mmcblkX/ro_lock_until_next_power_on

to lock the entire card (which will cover the boot partition too), with
echo 0 to unlock.

Other review comments:  I noticed that your pr_*(); statements are
missing "\n"s on the end, and you should add documentation on the new
sysfs nodes to:
   Documentation/mmc/mmc-dev-parts.txt

I think the overlap between your patch and Andrei's mmcblkXbootY/force_ro
node is going to be confusing -- one operates purely in the kernel and
the other is sent to the card.  Do you have any proposal for making the
difference clearer?

Thanks,

- Chris.
-- 
Chris Ball   <cjb@laptop.org>   <http://printf.net/>
One Laptop Per Child