[PATCH RFC v2] UBI: New ioctl() to support ubidump

[Artem Bityutskiy]

On Thu, 2014-07-31 at 11:01 +0800, hujianyang wrote:
> On 2014/7/30 23:53, Bill Pringlemeir wrote:
> > 
> > You can record the table if you know that the MTD is not changing.  If
> > you introduce the 'ioctl()' to the kernel, it will most likely be on an
> > active file system.  I guess this is a big decision in the tools design.
> 
> This ioctl() doesn't need UBIFS filesystem to be mounted, just needs
> UBI driver. We can keep this partition not active during this tool
> running.
> 
> But a properly configured kernel requirement you said in last mail
> worries me most. I think you are right and want to have a try. But
> I've discussed these stuff with Artem and he said, just quote:
> 
> ""
> So I envision that the tool would work like this.
> 
> $ ubidump my.img --lnum 5
>   - dump LEB 5, will need to scan the entire image.
> 
> $ ubidump /dev/ubiX_Y --lnum 5
>   - will just ask the UBI driver to give the PEB number for LEB 5, then
> find out the MTD device for this volume (should be possible by checking
> the sysfs files), and then reads the MTD device, and gets the UBI-level
> information from there.
> 
> Something like this, just quick thoughts.
> ""

Having a tool which does not need any kernel help is a lot more
preferable. I though we may have an ioctl like this if no one has time
to write full scanning support in user-space, and then maintain it.

> We can keep a temporary file to record the mapping table but that will
> make the initial submission much more complicated. But this way you
> mentioned to record the table should be considered to add into this tool
> in the future.

Hujianyang, AFAIU, right now you need an ability to dump UBIFS stuff.
You do not really need to know PEB number. So ubidump may
analyze /dev/ubiX_Y without knowing the PEB number, right? It can just
read from /dev/ubiX_Y directly. And print you all the UBIFS nodes.

I mean, if what user gives you is an UBI volume, you do not try going to
the MTD level.

-- 
Best Regards,
Artem Bityutskiy