Re: UBIFS: file data corruption during the power cut-off test

[Sergei Poselenov <sposelenov@xxxxxxxxxxx>]

Hello Richard,

On Thu, 6 Jun 2019 20:13:07 +0200 Richard Weinberger <richard.weinberger@xxxxxxxxx> wrote:

> On Thu, Jun 6, 2019 at 8:08 PM Sergei Poselenov <sposelenov@xxxxxxxxxxx> wrote:
> > This is understood. However, on the file length that is written to the partition, I'd expect that the file content will be the same as in the original file. This is not so.
> > Is it expected, or is it a deficiency of UBI?  
> 
> Please show in detail what you are doing, on syscall level, and what
> the expected output is.
> 

Here is my test:
/mnt/data1 # for i in `seq 0 99`; do
> dd if=/bin/busybox of=test${i}; done

During the  test, the board is powered off.

After bootup:
/mnt/data1 # ls -l
-rw-r--r--    1 root     root        396795 Jan  8 23:58 test0
-rw-r--r--    1 root     root        396795 Jan  8 23:58 test1
-rw-r--r--    1 root     root        113664 Jan  8 23:58 test2
/mnt/data1 #
/mnt/data1 # md5sum /bin/busybox *
23376319de62934c3859615e6244aae0  /bin/busybox
23376319de62934c3859615e6244aae0  test0
23376319de62934c3859615e6244aae0  test1
87cd1d1a28896e63eb039d75efef43a3  test2

As expected, test2 is shorter, hence has a different checksum.

Now, I' overwriting the content of the "test0" with "test2", without "test0" truncation:
mnt/data1 # dd if=test2 of=test0 conv=notrunc
222+0 records in
222+0 records out
113664 bytes (111.0KB) copied, 0.859668 seconds, 129.1KB/s
/mnt/data1 # md5sum *
23376319de62934c3859615e6244aae0  test0
23376319de62934c3859615e6244aae0  test1
87cd1d1a28896e63eb039d75efef43a3  test2
/mnt/data1 #

For this particular test pass, the content of test2 matches the content of the original file test0, so overwriting test0 with test2 doesn't change the data.

However, upon retry of the very same test from the beginning (with the power cut-off in the middle) it's easily to have the content of test2 (exactly the last 512 bytes in my case) which doesn't match test0, so "dd if=test2 of=test0 conv=notrunc" will result in test0 with a different checksum.

To remind, the partition is mounted with the "sync" option.

Thanks!

Regards,
Sergei


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