blkdev/dosfs/emmc issues.

[Gedare Bloom]

On Mon, Mar 13, 2017 at 11:05 AM, Tasslehoff Kjappfot
<tasskjapp at gmail.com> wrote:
>
>
> On Mon, Mar 13, 2017 at 3:48 PM, Gedare Bloom <gedare at rtems.org> wrote:
>>
>> On Mon, Mar 13, 2017 at 9:42 AM, Tasslehoff Kjappfot
>> <tasskjapp at gmail.com> wrote:
>> > A little update on this. I found out that if I do the following, the
>> > md5sum
>> > is wrong the second time I check it.
>> >
>> > 1. Write upgrade files
>> > 2. Check MD5
>> > 3. Unmount
>> > 4. Mount
>> > 5. Check MD5
>> >
>> What is the return value from unmount?
>
>
> unmount  is successful every time.

I did not think dosfs supports unmount() function so this is
surprising to me. How do you call it?

>>
>>
>> > If I do not unmount/mount, the MD5 is ok, even after a reboot.
>> >
>> > With JTAG I discovered that after I have initiated an unmount, the
>> > bdbuf_swapout_task tries to do 3 writes into blocks inside the file
>> > where
>> > the MD5 check fails. If I just ignore those writes, it also works.
>> >
>> Now that is strange. It may be worth it to inspect the
>> bdbuf_cache.modified and bdbuf_cache.sync chains. Those are what the
>> swapout task processes. A guess is maybe there is a race condition
>> between the two lists when the sync happens, and you are getting a
>> couple of extra writes.
>
>
> Sounds plausible. Is it possible to bypass/disable the bdbuf cache
> altogether? I have not configured anything related to SWAPOUT in my
> application, and the BDBUF setup is the following.
>
You can't entirely avoid it without changing the filesystem you use.

> #define CONFIGURE_BDBUF_MAX_READ_AHEAD_BLOCKS  (16)
> #define CONFIGURE_BDBUF_MAX_WRITE_BLOCKS       (64)
> #define CONFIGURE_BDBUF_BUFFER_MIN_SIZE        (512)
> #define CONFIGURE_BDBUF_BUFFER_MAX_SIZE        (32 * 1024)
> #define CONFIGURE_BDBUF_CACHE_MEMORY_SIZE      (4 * 1024 * 1024)
>
You may like to define a smaller CONFIGURE_SWAPOUT_BLOCK_HOLD
(and a smaller CONFIGURE_SWAPOUT_SWAP_PERIOD).

These two control the delay before swapout writes to disk.

>>
>>
>> You might also like to enable RTEMS_BDBUF_TRACE at the top of bdbuf.c
>> file.
>
>
> Thanks for the tip.
>
>