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

[hujianyang <hujianyang@huawei.com>]

On 2014/8/1 15:30, Artem Bityutskiy wrote:
> 
> There are 2 layers involved: MTD and UBI.
> 
> On the MTD level, the entire flash contents is available (/dev/mtdX)
> On the UBI level, only UBI volumes are available (/dev/ubiX_Y)
> 
> If I give you an UBI volume dump (cp /dev/ubiX_Y ubi.img), you will only
> see the contents of the UBI volume. If there was UBIFS file-system, you
> will see UBIFS nodes in the "ubi.img" file. You will not see UBI headers
> there.
> 
> The ideal design would be treating /dev/ubiX_Y the same way as
> 'ubi.img'. IOW:
> 
> ubidump ubi.img
> and
> ubidump /dev/ubiX_Y
> 
> should give the same results.
> 
> If I give you an MTD image (nanddump -o mtd.img /dev/mtdX), you should
> be able to see both UBIFS and UBI stuff in 'mtd.img'. You may see the
> same information in /dev/mtdX. To get the LEB<->PEB mapping, you need to
> do scanning, etc. So
> 
> ubidump mtd.img
> and
> ubidump /dev/mtdX
> 
> should be the same.
> 
> This is the basic picture.
> 
> Now what you want is to add an exception to this scheme. Namely, for the
> 'ubidump /dev/ubiX_Y' case: you want to get help from the driver, using
> the ioctl you introduced.
> 
> Frankly, I am not 100% sure this is a good idea, would be nice to hear
> from other people. I'd need to think a bit on this.
> 
> So what I suggested is the you do not submit this exception so far. Just
> teach ubidump to handle UBI volumes. I.e., make it work with
> 
> ubidump ubi.img
> ubidump /dev/ubiX_Y
> 

Oh, I've confused these things before. I want this utility work with
mtd.img and /dev/ubiX_Y. It seems they are not same.

> yes, these 2 will dump only ubifs stuff. Limited functionality.
> 
>> 1) No UBI stuff and read UBIFS stuff from UBI-driver
>> This is a easiest way and we don't need any ioctl either. We can't get
>> UBI-level stuff right now but we can put this into our design of dumping
>> an image file.
> 
> Yes. That's a good first step.
> 

How about writing a new version basing on this?

>> 2) Read data from MTD-driver and find a way to get pnum
>> This way is basing on my v2 work. We can put an ioctl() to kernel and
>> if kernel don't support this ioctl(), this tool will do a full-scan on
>> MTD device. It's transparent to user. But we should take some time to
>> consider how to do this full-scan.
> 
> I guess, I'd need to think some more about the ioctl(), and may be
> someone else suggests something.
> 

OK.


Have a good weekend~!

Hu