linux-kernel - Re: [PATCH v7 3/5] counter: Add character device interface

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Message-ID: <YBTrcYgbXfKYaQnX@shinobu>
Date:   Sat, 30 Jan 2021 14:15:29 +0900
From:   William Breathitt Gray <vilhelm.gray@...il.com>
To:     Oleksij Rempel <o.rempel@...gutronix.de>
Cc:     jic23@...nel.org, kamel.bouhara@...tlin.com, gwendal@...omium.org,
        a.fatoum@...gutronix.de, david@...hnology.com,
        linux-iio@...r.kernel.org, patrick.havelange@...ensium.com,
        alexandre.belloni@...tlin.com, mcoquelin.stm32@...il.com,
        linux-kernel@...r.kernel.org,
        Dan Carpenter <dan.carpenter@...cle.com>,
        kernel@...gutronix.de, fabrice.gasnier@...com,
        syednwaris@...il.com, linux-stm32@...md-mailman.stormreply.com,
        linux-arm-kernel@...ts.infradead.org, alexandre.torgue@...com
Subject: Re: [PATCH v7 3/5] counter: Add character device interface

On Thu, Jan 28, 2021 at 10:01:13AM +0100, Oleksij Rempel wrote:
> Hello William,
> 
> 
> On Fri, Dec 25, 2020 at 07:15:36PM -0500, William Breathitt Gray wrote:
> > This patch introduces a character device interface for the Counter
> > subsystem. Device data is exposed through standard character device read
> > operations. Device data is gathered when a Counter event is pushed by
> > the respective Counter device driver. Configuration is handled via ioctl
> > operations on the respective Counter character device node.
> > 
> > Cc: David Lechner <david@...hnology.com>
> > Cc: Gwendal Grignou <gwendal@...omium.org>
> > Cc: Dan Carpenter <dan.carpenter@...cle.com>
> > Signed-off-by: William Breathitt Gray <vilhelm.gray@...il.com>
> > ---
> ...
> > +struct counter_event {
> > +	__aligned_u64 timestamp;
> > +	__aligned_u64 value;
> > +	struct counter_watch watch;
> > +	__u8 errno;
> 
> This variable clashed in user space, as soon as you include errno.h,
> with the libc's "magic" definition of errno. What about "err" instead.
> I'm not sure it an __u8 is the proper type, IIRC usually it's an int.
> 
> Regards,
> Oleksij
> -- 
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Sure, I can rename this to avoid a possible clash with libc's errno.
Maybe "status" would be more apt to indicate that this is an exit status
for the event -- the code returned may simply be a warning and not
necessarily a critical error.

Regarding the datatype for this value, I've opened up the discussion in
my reply to David Lechner [1], so perhaps we can continue it there.

[1] https://lkml.org/lkml/2021/1/30/5

William Breathitt Gray

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