linux-kernel - Re: [PATCH] pps: add epoll support

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Message-ID: <f6bed779-6d59-4f0f-8a59-b6312bd83b4e@enneenne.com>
Date: Wed, 26 Feb 2025 08:36:49 +0100
From: Rodolfo Giometti <giometti@...eenne.com>
To: Denis OSTERLAND-HEIM <denis.osterland@...hl.com>
Cc: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] pps: add epoll support

On 25/02/25 17:34, Denis OSTERLAND-HEIM wrote:
> Hi,
> 
>> -----Original Message-----
>> From: Rodolfo Giometti <giometti@...eenne.com>
>> Sent: Tuesday, February 25, 2025 3:24 PM
>> To: Denis OSTERLAND-HEIM <denis.osterland@...hl.com>
>> Cc: linux-kernel@...r.kernel.org
>> 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@...uxfoundation.org>
     Andrew Morton <akpm@...ux-foundation.org>

And explain the goal of the patch within the description.

Thanks a lot!

Ciao,

Rodolfo

-- 
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