[PATCH 6/6] [MTD-UTILS] nandwrite: Add Support for Reading from Standard Input

[Grant Erickson]

On 9/8/08 9:14 AM, Ladislav Michl wrote:
> On Sun, Sep 07, 2008 at 09:29:19PM -0700, Grant Erickson wrote:
>> Added suppport for reading in band data from standard input based on a
>> patch originally generated by Richard Titmuss <titmuss at slimdevices.com>
>> at 
>> <http://lists.slimdevices.com/pipermail/jive-checkins/2008-May/001918.html>.
>> 
>> Signed-off-by: Grant Erickson <gerickson at nuovations.com>
>> ---
>> 
>> In addition to the above patch, further discussion of this feature was
>> raised by Tommi Airikka <tommi.airikka at ericsson.com> at
>> <http://lists.infradead.org/pipermail/linux-mtd/2008-September/022913.html>.
> 
> Hmm, so long I was defered with implementing this feature, that someone
> else did it :-)
> 
> Anyway, let me raise few objections:

Fair enough.

However, considering that there is sufficient desire for this feature and it
has been implemented several times (a number of them off-list and never
submitted) let me propose getting this in place and in tree as-is and then
evolving and improving it.

> - code uses lseek. Obviously, you cannot seek on pipe.

True enough. The patch avoids the lseek to determine input file size;
however, did not address the 'markbad' recovery lseek case.

Short-term proposal: like 'writeoob', disable 'markbad' support when reading
from standard input and condition the whole 'markbad' logic on not reading
from standard input.

> - there is no need to use "invariant placeholder". What about simply
>   read till file ends?

Perhaps Richard can comment on his motivation here. I would suggest that the
loop termination condition is not quite that simple since the termination
cases are 1) there is no more input data to read (error or EOF) or 2) we
have moved outside of the output device bounds.

> - there is no need to use special case for reading from stdin...

The patch as-is from Richard did for whatever reasons he chose to go that
route. Perhaps he can comment on his motivations.

However, there may be an opportunity to unify the regular file versus
standard input cases along with adding support for '-l,--length=length'.

> So what about:
>
> while (not eof)
>   read page (and oob if selected) data into buffer

What about a short read in which you only get part of a page or a whole page
and part of the OOB data? Bail out? Best effort?

> next:
> if (write buffer fails)
>   mark bad, select next page, goto next
>
> Reading from stdin would imply padding. Care to implement that?

For the time being, padding must be explicitly requested.

> PS: It is remotely possible that one day I do it myself, but I'm
> notoriously slow on doing things I do not urgently need.

Understood and agreed.

For the present, the patch satisfies my cited use case (clearly those of
Richard and hopefully those of Tommi) and given the value added, I'd
advocate its inclusion and incremental evolution through future patches.

Regards,

Grant