Re: How do you wipe a UBI filesystem?

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