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Date:   Tue, 29 Dec 2020 21:35:13 -0800
From:   Joe Perches <joe@...ches.com>
To:     Peng Wang <rocking@...ux.alibaba.com>, apw@...onical.com
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH] checkpatch: ignore warning designated initializers
 using NR_CPUS

On Wed, 2020-12-30 at 12:13 +0800, Peng Wang wrote:
> Some max_length wants to hold as large room as possible to
> ensure enough size to tackle with the biggest NR_CPUS. As
> an example below:
> 
> kernel/cgroup/cpuset.c:
> static struct cftype legacy_files[] = {
>         {
>                 .name = "cpus",
>                 .seq_show = cpuset_common_seq_show,
>                 .write = cpuset_write_resmask,
>                 .max_write_len = (100U + 6 * NR_CPUS),
>                 .private = FILE_CPULIST,
>         },
> 	...
> }
[]
> diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
[]
> @@ -7022,12 +7022,15 @@ sub process {
>  
> 
>  # use of NR_CPUS is usually wrong
>  # ignore definitions of NR_CPUS and usage to define arrays as likely right
> +# ignore designated initializers using NR_CPUS
> +
>  		if ($line =~ /\bNR_CPUS\b/ &&
>  		    $line !~ /^.\s*\s*#\s*if\b.*\bNR_CPUS\b/ &&
>  		    $line !~ /^.\s*\s*#\s*define\b.*\bNR_CPUS\b/ &&
>  		    $line !~ /^.\s*$Declare\s.*\[[^\]]*NR_CPUS[^\]]*\]/ &&
>  		    $line !~ /\[[^\]]*\.\.\.[^\]]*NR_CPUS[^\]]*\]/ &&
> -		    $line !~ /\[[^\]]*NR_CPUS[^\]]*\.\.\.[^\]]*\]/)
> +		    $line !~ /\[[^\]]*NR_CPUS[^\]]*\.\.\.[^\]]*\]/ &&
> +		    $line !~ /\s*\..*=.*\bNR_CPUS\b.*,$/)
>  		{
>  			WARN("NR_CPUS",
>  			     "usage of NR_CPUS is often wrong - consider using cpu_possible(), num_possible_cpus(), for_each_possible_cpu(), etc\n" . $herecurr);

I wonder if it's worth it as there just aren't many of these: (6 total)

$ git grep -P '\..*=.*\bNR_CPUS\b.*,\s*$'
drivers/firmware/efi/efi.c:     .cpu_bitmap             = { [BITS_TO_LONGS(NR__CPUS)] = 0},
drivers/infiniband/hw/hfi1/sdma.c:      .max_size = NR_CPUS,
init/init_task.c:       .nr_cpus_allowed= NR_CPUS,
kernel/cgroup/cpuset.c:         .max_write_len = (100U + 6 * NR_CPUS),
kernel/cgroup/cpuset.c:         .max_write_len = (100U + 6 * NR_CPUS),
kernel/sysctl.c:                .maxlen         = NR_CPUS,

It also seems it might be more sensible as:

	$line !~ /^.\s*\.\w+\s*=\s*.*\bNR_CPUS\b/

Which finds a couple more:

$ git grep -P '^\s*\.\w+\s*=\s*.*\bNR_CPUS\b'
arch/arm64/include/asm/processor.h:     .fpsimd_cpu = NR_CPUS,                  \
arch/powerpc/kernel/prom_init.c:                .max_cpus = cpu_to_be32(NR_CPUS),       /* number of cores supported */
drivers/firmware/efi/efi.c:     .cpu_bitmap             = { [BITS_TO_LONGS(NR_CPUS)] = 0},
drivers/infiniband/hw/hfi1/sdma.c:      .max_size = NR_CPUS,
init/init_task.c:       .nr_cpus_allowed= NR_CPUS,
kernel/cgroup/cpuset.c:         .max_write_len = (100U + 6 * NR_CPUS),
kernel/cgroup/cpuset.c:         .max_write_len = (100U + 6 * NR_CPUS),
kernel/sysctl.c:                .maxlen         = NR_CPUS,


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