UBI/ubifs problem

[Ricard Wanderlof]

I posted this query yesterday, but the information I provided was rather 
short, so here's another attempt with more info which hopefully will 
trigger some response.

I have two ubifs images made with mkfs.ubifs:

-rw-rw-r-- 1 ricardw users 20256768 2012-02-16 11:12 rootfs.img
-rw-rw-r-- 1 ricardw users  2064384 2012-02-16 11:09 rwfs.img

On my target system I attach mtd5 to UBI and create two volumes:

ubiattach -m 5 /dev/ubi_ctrl
ubimkvol -N rootfs -n 4 -t static -s 25165824 /dev/ubi0
ubimkvol -N rwfs -n 5 -t dynamic -S 30 /dev/ubi0

30 LEBs in the flash I'm using is about 30 * 126 KiB = 3.7 MiB .

I then write the volumes with the image data

ubiupdatevol /dev/ubi0_4  ./rootfs.img
ubiupdatevol /dev/ubi0_5 ./rwfs.img

Now I mount ubi0:rootfs on /mnt/1:

mount -t ubifs ubi0:rootfs /mnt/1/

which results in

UBIFS: mounted UBI device 0, volume 4, name "rootfs"
UBIFS: mounted read-only
UBIFS: file system size:   23869440 bytes (23310 KiB, 22 MiB, 185 LEBs)
UBIFS: journal size:       9033728 bytes (8822 KiB, 8 MiB, 71 LEBs)
UBIFS: media format:       w4/r0 (latest is w4/r0)
UBIFS: default compressor: lzo
UBIFS: reserved for root:  0 bytes (0 KiB)

All is well so far. Now I attempt to mount ubi0:rwfs on /mnt/2:

mount -t ubifs ubi0:rwfs /mnt/2

which results in

UBIFS error (pid 2965): validate_sb: bad superblock, error 8
mount: Mounting ubi0:rwfs on /mnt/2 failed: Invalid argument

If I now remove the rwfs volume using ubirmvol, and create a new one that 
is 78 LEBs in size (smaller sizes yield the same error message), again 
ubiupdatevol the same rwfs.img image, and attempt to mount it, I get:

UBIFS: reserved for root:  0 bytes (0 KiB)
UBIFS: mounted UBI device 0, volume 5, name "rwfs"
UBIFS: file system size:   8644608 bytes (8442 KiB, 8 MiB, 67 LEBs)
UBIFS: journal size:       9033728 bytes (8822 KiB, 8 MiB, 71 LEBs)
UBIFS: media format:       w4/r0 (latest is w4/r0)
UBIFS: default compressor: lzo
UBIFS: reserved for root:  0 bytes (0 KiB)

The thing that really puzzles me here is that the 2 MiB ubifs image shows 
up as an 8 MiB 'file system size' when mounted. It does explain why 78 
LEBs are required though.

Furthermore, df says:

ubi0:rootfs              21212     17652      3560  83% /mnt/1
ubi0:rwfs                 7228       432      6796   6% /mnt/2

which correlates with the statistics from ubifs above, but it seems odd 
that I can't create a volume with more than 6% utilization. If I start to 
fill the volume with files after mounting, I can get up to 100% use.

At any rate, the error message is odd, especially given that ubiupdatevol 
didn't report any problems.

I've also tried using a static volume for rwfs, with the same results (and 
of course I can't write to it so I can't put more files on it in that 
case).

Even considering the overhead that the rootfs volume appears to need 
(image size is 20256768 and ubifs reports a 'file system size' of 
23869440), i.e. an overhead of 3612672 bytes), it doesn't add up; adding 
3612672 to the rwfs.img image size of 2064384 would result in a total size 
of 5677056, not 8644608.

Could there be compressed files in the rwfs.img image that somehow need to 
be expanded in the flash?

It's not that we're pressed for space and need the size, but I'd like to 
understand what is going on. I don't really think this is a bug, more 
something that I don't understand. I can't find anything on the mtd 
documentation pages that seem to relate to this though.

For the record, I'm using Linux 2.6.35 .

/Ricard
-- 
Ricard Wolf Wanderlöf                           ricardw(at)axis.com
Axis Communications AB, Lund, Sweden            www.axis.com
Phone +46 46 272 2016                           Fax +46 46 13 61 30