From mboxrd@z Thu Jan  1 00:00:00 1970
From: Sumit Garg <sumit.garg@linaro.org>
Date: Thu, 7 Mar 2019 14:54:41 +0530
Subject: [LTP] [PATCH v2 1/2] syscalls/sync_file_range: add partial file
	sync test-case
In-Reply-To: <20190306085418.GA14290@rei>
References: <1551770065-20444-1-git-send-email-sumit.garg@linaro.org>
 <20190305141903.GD13703@rei>
 <CAFA6WYOPW0mkmGFbcZRmvhXsOJouUi1d-rcV_-sgKVKpkqSMSA@mail.gmail.com>
 <20190306085418.GA14290@rei>
Message-ID: <CAFA6WYMnLKkSAPjxQu-gn6xiPx2Pc5hRCbyrkZF1x51HZNz5PA@mail.gmail.com>
List-Id: <ltp.lists.linux.it>
MIME-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
To: ltp@lists.linux.it

On Wed, 6 Mar 2019 at 14:24, Cyril Hrubis <chrubis@suse.cz> wrote:
>
> Hi!
> > > Looking at this the function is nearly the same as the other one, I
> > > guess that we may as well define the function as:
> > >
> > > static void verify_sync_file_range(off64_t off, off64_t size, char byte)
> > > {
> > >         ...
> > > }
> > >
> >
> > Yeah it could be made common. But we may not be able to reuse it for
> > third case you mentioned below.
>
> We may as well add offset and size for the write as well.
>

Ok.

> > > Also I'm not sure I was clear enough, but I was suggesting to check for
> > > upper bound for the synced size as well, which is why I suggested to do
> > > full write, sync only part of it, then check that the size was within
> > > bounds, i.e. >= size and  <= size + epsilon.
> > >
> >
> > Do you see any value add of upper bound check? AFAIK, device writes
> > continue in back-end and we might not be sure about appropriate value
> > for "epsilon".
>
> AFAIK this makes sense as far the file written fits into RAM buffers.
> We do write followed by a sync that asks particular range to be written
> to the device, so unless we manage to write significant portion of the
> file while we are calling the write syscall in a loop we will get quite
> close to the expectations. I guess that we can also check how much data
> was written right after we finished writing to the file and if that
> number is neglectible it would be fairly safe to check for upper bound.
> Does that sound reasonable to you?
>

Yes, I see number is negligible after write to file. So will add this
upper bound check with epsilon = 10%.

-Sumit

> > > I guess that we can even extend this to call the sync over a range that
> > > has been only partially written, but for that we would have to be
> > > careful and make sure all the data has been either synced at the end of
> > > the test function or use a different file for each test.
> > >
> >
> > I think using different file for each case looks more appropriate.
>
> Agreed.
>
> --
> Cyril Hrubis
> chrubis@suse.cz