Re: [PATCH] pps: add epoll support

[Rodolfo Giometti]

On 25/02/25 17:34, Denis OSTERLAND-HEIM wrote:
> Hi,
>
> > -----Original Message-----
> > From: Rodolfo Giometti <giometti@xxxxxxxxxxxx>
> > Sent: Tuesday, February 25, 2025 3:24 PM
> > To: Denis OSTERLAND-HEIM <denis.osterland@xxxxxxxxx>
> > Cc: linux-kernel@xxxxxxxxxxxxxxx
> > Subject: Re: [PATCH] pps: add epoll support
> >   
> [snip]
> > > If I start multiple user space programs data races are visible.
> > >
> > > ```
> > > # for i in 0 1 2 3 4 5 6; do PpsPollTest /dev/pps1 > log$i & done
> > > # sleep 6
> > > # tail log*
> > > ==> log0 <==
> > > timeout
> > > assert: 196
> > > time: 1520599554.276752928
> > > assert: 197
> > > time: 1520599555.300692704
> >
> > This is the same behavior we have when working with a serial port: if more than
> > one process gets access to it, data is stolen.
> Okay, then lets choose your suggestion.
>
> > > >From my point of view it would be great to fix this bug without such an limitation.
> >
> > I disagree, it is not a limitation! It is like a normal char device work.
> >
> > What we have to test now is if your initial goal has been addressed! That is, in
> > an application that has more to do than just dealing with one PPS device, we can
> > use poll()/select() in order to avoid using threads.
> I will do the final test.

Try poll() by using a process workin on multiple pps sources.

> I expect that it works with your patch.

:)

> Shall I prepare the patch?

Yes.

> Shall I add you as Co-author?

Yes. Add my name in the Signed-off-by: line and, please, send to me a preview.

> Or do you want to send your patch with me in reported-by and tested-by?
>
> Fixes: eae9d2ba0cfc ("LinuxPPS: core support")?

OK.

> CC stable?

    Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
    Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>

And explain the goal of the patch within the description.

Thanks a lot!

Ciao,

Rodolfo

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