Re: errors copying UBI volumes

[Sascha Hauer <s.hauer@pengutronix.de>]

Hi Giorgio,

On Wed, Sep 14, 2016 at 05:52:32PM +0200, iw3gtf@arcor.de wrote:
> Hi,
> 
> I'm working on an embedded board with an iMX25 arm CPU and a nand flash.
> 
> The board runs a linux kernel/userland.
> 
> When the user updates the firmware, the running userland/kernel creates some
> new ubi volumes on the nand, let's say 'kernel_next' and 'userland_next'.
> On the next system reboot barebox looks if it finds, lets say, the 'kernel_next' volume
> and, in this case, it removes the old one ('kernel'), creates a new, empty one ('kernel'),
> copies 'kernel_next' to the just created 'kernel' and finally removes the 'kernel_next'
> to complete the update.

While this should work, why so complicated? Since this commit:

| commit 892abde56c1c5a62d49d8b70c73e5d388e74345d
| Author: Richard Weinberger <richard@nod.at>
| Date:   Mon Nov 24 22:30:10 2014 +0100
|
|    UBI: rename_volumes: Use UBI_METAONLY
|    
|    By using UBI_METAONLY in rename_volumes() it is now possible to rename
|    an UBI volume atomically while it is open for writing.
|    This is useful for firmware upgrades.

It should be possible to just remove 'kernel' and rename 'kernel_next' to 'kernel'
without bootloader intervention.

BTW you should consider using Bootloader Spec entries
(http://www.barebox.org/doc/latest/user/booting-linux.html#bootloader-spec).
This makes the kernel volume unnecessary and the kernel will only be a file
in UBIFS and thus updating is a matter of 'cp newkernel /boot/kernel'.
Also booting in barebox becomes as simple as 'boot nand0.ubi.rootfs', no
further configuration or scripting required.

> 
> Here the relevant part of the init script:
> 
> ...
> 	if [ -e $kernel_next ]; then
> 		echo "Update the kernel... "
> 		ubirmvol $ubi_root kernel
> 		ubimkvol $ubi_root kernel 8M
> 		cp $kernel_next $kernel
> 		if [ $? != 0 ]; then
> 			echo "***Errors copying $kernel_next to $kernel"
> 			sleep 2
> 		else
> 			echo "Update OK."
> 			ubirmvol $ubi_root kernel_next
> 		fi
> 	fi
> ...
> 
> Now, after updating the barebox version to the current one, v2016.09.0, the 'cp' command
> produces an almost endless sequence of failed assertions and stask backtraces:
> 
> ...
> UBI assert failed in ubi_eba_read_leb at 359
> Function entered at [<87053010>] from [<87018ce0>]
> Function entered at [<87018ce0>] from [<87017fb4>]
> Function entered at [<87017fb4>] from [<8703f100>]
> Function entered at [<8703f100>] from [<8703f2cc>]
> Function entered at [<8703f2cc>] from [<8703faf8>]
> Function entered at [<8703faf8>] from [<87039e78>]
> Function entered at [<87039e78>] from [<87029178>]
> Function entered at [<87029178>] from [<87003614>]
> Function entered at [<87003614>] from [<87008e0c>]
> Function entered at [<87008e0c>] from [<870083a0>]
> Function entered at [<870083a0>] from [<8700908c>]
> Function entered at [<8700908c>] from [<870011cc>]
> Function entered at [<870011cc>] from [<870515d4>]
> Function entered at [<870515d4>] from [<80052648>]
> UBI assert failed in ubi_eba_read_leb at 359
> Function entered at [<87053010>] from [<87018ce0>]
> Function entered at [<87018ce0>] from [<87017fb4>]
> Function entered at [<87017fb4>] from [<8703f100>]
> Function entered at [<8703f100>] from [<8703f2cc>]
> Function entered at [<8703f2cc>] from [<8703faf8>]
> Function entered at [<8703faf8>] from [<87039e78>]
> ...

Please enable KALLSYMS to make this readable.

> 
> After trying different things I realized that 'cp' has problems
> only with UBI volumes that were created by the kernel/userland
> during the firmware update process; if I create a volume within
> barebox it just work as expected.
> 
> Here is the source code snippet with the failing assertion:
> (file <barebox_root>/drivers/mtd/ubi/eba.c)
> 
> int ubi_eba_read_leb(struct ubi_device *ubi, struct ubi_volume *vol, int lnum,
> 		     void *buf, int offset, int len, int check)
> {
> ...
> 	pnum = vol->eba_tbl[lnum];
> 	if (pnum < 0) {
> 		/*
> 		 * The logical eraseblock is not mapped, fill the whole buffer
> 		 * with 0xFF bytes. The exception is static volumes for which
> 		 * it is an error to read unmapped logical eraseblocks.
> 		 */
> 		dbg_eba("read %d bytes from offset %d of LEB %d:%d (unmapped)",
> 			len, offset, vol_id, lnum);
> 		leb_read_unlock(ubi, vol_id, lnum);
> 		ubi_assert(vol->vol_type != UBI_STATIC_VOLUME);
> 		memset(buf, 0xFF, len);
> 		return 0;
> 	}

Have you created 'kernel_next' and/or 'userland_next' as static volume
(-t=static)? The comment above states that in static volumes you cannot
read unmapped logical eraseblocks. When wou do not completely fill
'kernel_next' with data then you can only read up to the point to which
it is filled, the remaining LEBs are unmapped and thus unreadable.
Note that when you hit the unmapped LEBs then you have already read all
data; the errors only occur on the free space. This is the reason you
can still boot the new system.

Sascha

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