Re: UBI: badblock management confusion!

[Adrian Hunter <ext-adrian.hunter@nokia.com>]

ext Nancy wrote:
> On Fri, Apr 25, 2008 at 6:47 PM, Adrian Hunter
> <ext-adrian.hunter@nokia.com> wrote:
>> ext Nancy wrote:
>>> Hi all,
>>>        I don't quite understand the UBI badblock management unit.
>>> But I think there must be something wrong, or I take a wrong operation.
>>>        Please follow my test below:
>>>
>>> # ubiformat /dev/mtd5
>>> ubiformat: mtd5 (NAND), size 536870912 bytes (512.0 MiB), 262144
>> eraseblocks of
>>> 262144 bytes (256.0 KiB), min. I/O size 2048 bytes
>>> libscan: scanning eraseblock 2047 -- 100 % complete
>>> ubiformat: 2045 eraseblocks have valid erase counter, mean value is 23
>>> ubiformat: bad eraseblocks: 10, 40, 84
>>> ubiformat: formatting eraseblock 2047 -- 100 % complete
>>>
>>> # modprobe ubi mtd=5
>>> UBI: physical eraseblock size:   262144 bytes (256 KiB)
>>> UBI: logical eraseblock size:    258048 bytes
>>> UBI: smallest flash I/O unit:    2048
>>> UBI: VID header offset:          2048 (aligned 2048)
>>> UBI: data offset:                4096
>>> UBI: attached mtd5 to ubi0
>>> UBI: MTD device name:            "NAND VFAT partition"
>>> UBI: MTD device size:            512 MiB
>>> UBI: number of good PEBs:        2045
>>> UBI: number of bad PEBs:         3
>>> UBI: max. allowed volumes:       128
>>> UBI: wear-leveling threshold:    256
>>> UBI: number of internal volumes: 1
>>> UBI: number of user volumes:     0
>>> UBI: available PEBs:             2021
>>> UBI: total number of reserved PEBs: 24
>>> UBI: number of PEBs reserved for bad PEB handling: 20
>>> UBI: max/mean erase counter: 38/24
>>> UBI: background thread "ubi_bgt0d" started, PID 233
>>>
>>>
>> ***************************************************************************
>>> I'm going to make one big volume which take all available space this ubi
>>> device has.
>>>
>>> I think the volume size should be equal to
>>> (total number of PEB this ubi device has - total number of reserved PEBs)
>> \
>>> * LEB size
>>> In this case, it should be : (2048-24) * 258048 bytes
>>>
>>> But that is not what UBI count.
>>> UBI think the volume size
>>> = (number of good PEBs - total number of reserved PEBs) * LEB size
>>>
>>> Q: Number of bad PEBs at initialization are not included in resered for
>> bad
>>> PEBs handling. That mean there should never has badblocks overflow issue
>>> happen. What a good idea! But is there really a possible way to implement
>> this
>>> idea?
>>>
>> It does work.
>>
>>
>>>   Suppose there's only one volume take all the ubi device space, there's
>> no
>>> badblocks at the very beginning. The user does never shut down the device
>> but
>>> hibernate for a long time. Then, suppose there is 3 badblocks and the
>> volume
>>> just full of data. No space left. Then reboot the device, beside the 3
>> badblocks
>>> which used to be count in reserved PEBs, now be seperate from the reserved
>> PEBs,
>>> But there's no space, reserved PEB will fail.
>>>
>> No, there will just be a warning - as shown in your test:
>>
>>
>>        UBI warning: ubi_eba_init_scan: cannot reserve enough PEBs for bad
>> PEB handling, reserved 19, need 20
>>
>> There *would* be problem if you marked 21 bad and only 20 were reserved for
>> bad block handling.
>>
>>
>>>   The following test showes even the volume data is blank, there still
>> comes
>>> problem.
>>>   Is it an UBI bug or my wrong operation?
>>>
>> Your wrong operation.
>>
>>
>>
>>>   Thanks for your notice about it!
>>>
>> ****************************************************************************
>>> # ubimkvol /dev/ubi0 -n 0 -N vfat -s 509292KiB
>>> Volume ID 0, size 2021 LEBs (521515008 bytes, 497.4 MiB), LEB size
>>> 258048 bytes (252.0 KiB), dynamic, name "vfat", alignment 1
>>> # rmmod ubi
>>> UBI: mtd5 is detached from ubi0
>>>
>>>
>> *****************************************************************************
>>> "markbadblock" is a tool I force to mark a block bad manually, just for
>> test
>> *****************************************************************************
>>> # markbadblock -l 17 /dev/mtd5
>>> Block size 262144, page size 2048, OOB size 64
>>> mark block 17 to be badblock done
>>>
>>> # modprobe ubi mtd=5
>>> UBI: physical eraseblock size:   262144 bytes (256 KiB)
>>> UBI: logical eraseblock size:    258048 bytes
>>> UBI: smallest flash I/O unit:    2048
>>> UBI: VID header offset:          2048 (aligned 2048)
>>> UBI: data offset:                4096
>>> UBI warning: ubi_eba_init_scan: cannot reserve enough PEBs for bad PEB
>>> handling, reserved 19, need 20
>>> UBI: attached mtd5 to ubi0
>>> UBI: MTD device name:            "NAND VFAT partition"
>>> UBI: MTD device size:            512 MiB
>>> UBI: number of good PEBs:        2044
>>> UBI: number of bad PEBs:         4
>>> UBI: max. allowed volumes:       128
>>> UBI: wear-leveling threshold:    256
>>> UBI: number of internal volumes: 1
>>> UBI: number of user volumes:     1
>>> UBI: available PEBs:             0
>>> UBI: total number of reserved PEBs: 2044
>>> UBI: number of PEBs reserved for bad PEB handling: 19
>>> UBI: max/mean erase counter: 39/24
>>> UBI: background thread "ubi_bgt0d" started, PID 263
>>> # modprobe ubifs
>>>
>>> # mount -t ubifs ubi0:ubifs /mnt/1
>>> UBIFS error (pid 293): ubifs_get_sb: cannot open "ubi0:ubifs", error -19
>>>
>> You named the volume "vfat" (-N option of ubimkvol), but you are trying
>> to mount a volume named "ubifs" i.e. should be:
>>
>>        mount -t ubifs ubi0:vfat /mnt/1
> 
> Oh, thank you for ponting out my mistake!
> You mean UBI admit the amount of current badblocks are part of
> reserved PEBs, right?

Not exactly.  It is just that UBI does not mind if there are not enough
PEBs to meet the number desired for bad-block handling.

> If the answer is yes, then the volume size I'm goting to create should
> be equal to
> 
> (total number of PEB this ubi device has - total number of reserved
> PEBs) * LEB size
> 
> not what UBI think:
> (number of good PEBs - total number of reserved PEBs) * LEB size
> 
> Am I right?

I am not sure what you are trying to achieve.  You can always use
the -m option of ubimkvol to set volume size to maximum available size.