[PATCH] mtdcore: add writeable attribute in sysfs

[Couret Charles-Antoine]

Le 20/04/2018 à 21:43, Boris Brezillon a écrit :
> Hi Charles-Antoine,
Hi,
> Hm, why don't you remove the RO constraint on such partitions then? I
> mean, if the device can be written, even rarely, it's no longer a
> read-only device.
Sometimes the partition is set as read-only but it is not the case in 
reality, it is only a software flag.
 From my experience, it is often to protect the bootloader to be changed 
from Linux system. To avoid corruption (or to get full control)
>> Or to protect the device without using mtdro virtual device to read the content.
> What's the point? Only root can access /dev/mtdX. Looks like you want
> to protect against inadvertent write to the wrong MTD dev, but I'm not
> sure this is the kernel responsibility to enforce that.
Yes the idea is to keep (or to set) this additional protection and 
having a way to by-pass only when it is relevant (to make an update or 
to do something special).
I am not sure that is a big deal to add this change on the kernel, the 
code is very light and simple.
> Missing Signed-off-by tag.
Thanks, I will add that.
> Please align parameters on the open-parenthesis.
Thanks, sorry for this issue.
>
> What happens if you turn a RW device into a RO while it's still being
> used by someone? Not sure at all this is safe.
>
> Regards,
>
> Boris
The writeable flag is checked before the write operation. If this flag 
is cleared while a process is writing something, the write operation can 
be completed. But after this completion, no other write operations are 
allowed.

I will make some tests tomorrow to check this part. But normally that 
should not be an issue.
Regards,
Charles-Antoine Couret