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How do you wipe a UBI filesystem?

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  How do you wipe a UBI filesystem? Grant Edwards <invalid@invalid.invalid> - 2025-02-05 19:30 +0000
    Re: How do you wipe a UBI filesystem? Grant Edwards <invalid@invalid.invalid> - 2025-02-05 21:15 +0000
    Re: How do you wipe a UBI filesystem? chrisq <devzero@nospam.com> - 2025-02-12 15:03 +0000
      Re: How do you wipe a UBI filesystem? Grant Edwards <invalid@invalid.invalid> - 2025-02-12 18:03 +0000

#32328 — How do you wipe a UBI filesystem?

Pretend I've got an MTD partition attached as a UBI device.

That UBI device contains a couple differen UBI volumes.

In one of those volumes is a UBIFS filesystem that has a bunch of
files in it.

I've done some googling, but all of the answers are "use
ubiformat". That will wipe the whole device. I just want to
re-initialize one ubifs filesytem in one volume -- not the whole
ubi device.

How do I wipe that filesystem (set it back to empty).  Do I need to
create an empty ubifs "image" file using mkfs.ubifs and then use
ubiupdatevol to write that image to the volume?

Isn't there a simpler way?

-- 
Grant

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#32329

On 2025-02-05, Grant Edwards <invalid@invalid.invalid> wrote:
> Pretend I've got an MTD partition attached as a UBI device.
>
> That UBI device contains a couple differen UBI volumes.
>
> In one of those volumes is a UBIFS filesystem that has a bunch of
> files in it.
>
> I've done some googling, but all of the answers are "use
> ubiformat". That will wipe the whole device. I just want to
> re-initialize one ubifs filesytem in one volume -- not the whole
> ubi device.
>
> How do I wipe that filesystem (set it back to empty).  Do I need to
> create an empty ubifs "image" file using mkfs.ubifs and then use
> ubiupdatevol to write that image to the volume?
>
> Isn't there a simpler way?

I've figured out two other ways to do it:

    ubiupdatevol -t /dev/ubiX_Y
    mount -t ubifs /dev/ubiX:volname /mnt/point

That works, but apparently that erases every block in the
volume. That's a lot of unecessary wear.  Surely you can "empty" the
filesystem without erasing every block in the volume (when probably
90% of the blocks have never been written).

Another option:

    ubirmvol /dev/ubiX -N volname
    umimkvol /dev/ubiX -N volname -m
    mount -t ubifs /dev/ubiX:volname /mnt/point

That too seems to work, but modifying the devices volume table/list
seems a bit risky compared to simply re-initializing the filesystem
inside an existing volume.


  

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#32330

On 2/5/25 19:30, Grant Edwards wrote:
> Pretend I've got an MTD partition attached as a UBI device.
> 
> That UBI device contains a couple differen UBI volumes.
> 
> In one of those volumes is a UBIFS filesystem that has a bunch of
> files in it.
> 
> I've done some googling, but all of the answers are "use
> ubiformat". That will wipe the whole device. I just want to
> re-initialize one ubifs filesytem in one volume -- not the whole
> ubi device.
> 
> How do I wipe that filesystem (set it back to empty).  Do I need to
> create an empty ubifs "image" file using mkfs.ubifs and then use
> ubiupdatevol to write that image to the volume?
> 
> Isn't there a simpler way?
> 

Try a search:

"ubi file system utilities Linux"

Which may help, third entry down ?.

Chris

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#32333

On 2025-02-12, chrisq <devzero@nospam.com> wrote:
> On 2/5/25 19:30, Grant Edwards wrote:
>> Pretend I've got an MTD partition attached as a UBI device.
>> 
>> That UBI device contains a couple differen UBI volumes.
>> 
>> In one of those volumes is a UBIFS filesystem that has a bunch of
>> files in it.
>> 
>> I've done some googling, but all of the answers are "use
>> ubiformat". That will wipe the whole device. I just want to
>> re-initialize one ubifs filesytem in one volume -- not the whole
>> ubi device.
>> 
>> How do I wipe that filesystem (set it back to empty).  Do I need to
>> create an empty ubifs "image" file using mkfs.ubifs and then use
>> ubiupdatevol to write that image to the volume?
>> 
>> Isn't there a simpler way?
>
> Try a search:
>
> "ubi file system utilities Linux"
>
> Which may help, third entry down ?.

The answer is 'ubiupdatevol -t' (bracketed by umount/mount commands).

I had figured out that command worked, but one tutorial/blog I found
stated that it erased every block in the volume.  The way it was
described it sounded like doing a 'ubiupdatevol -t' on a 20MB volume
would erase 20MB of flash -- even if that volume contained a
filesystem with only a few small files in it.

So I was reluctant to use it because of the uneccessary wear on the
flash when used on volumes that were mostly empty.  It turns out that
blog was wrong/misleading.

The truncate operation doesn't erase any blocks. It _unmaps_ any
_programmed_ blocks that are currently in use in the volume. Those
blocks will later be erased and put back in the "free" pool during
garbage collection.  No blocks are erased either unnecessarily or by
the command itself.

--
Grant

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