Re: [PATCH] checkpatch: fix CONST_STRUCT when const_structs.checkpatch is missing

[Joe Perches <joe@perches.com>]

On Mon, 2020-06-22 at 21:48 +0100, Quentin Monnet wrote:
> Checkpatch reports warnings when some specific structs are not declared
> as const in the code. The list of structs to consider was initially
> defined in the checkpatch.pl script itself, but it was later moved to an
> external file (scripts/const_structs.checkpatch). This introduced two
> minor issues:
> 
> - When file scripts/const_structs.checkpatch is not present (for
>   example, if checkpatch is run outside of the kernel directory with the
>   "--no-tree" option), a warning is printed to stderr to tell the user
>   that "No structs that should be const will be found". This is fair,
>   but the warning is printed unconditionally, even if the option
>   "--ignore CONST_STRUCT" is passed. In the latter case, we explicitly
>   ask checkpatch to skip this check, so no warning should be printed.
> 
> - When scripts/const_structs.checkpatch is missing, or even when trying
>   to silence the warning by adding an empty file, $const_structs is set
>   to "", and the regex used for finding structs that should be const,
>   "$line =~ /\bstruct\s+($const_structs)\b(?!\s*\{)/)", matches all
>   structs found in the code, thus reporting a number of false positives.
> 
> Let's fix the first item by skipping scripts/const_structs.checkpatch
> processing if "CONST_STRUCT" checks are ignored, and the second one by
> skipping the test if $const_structs is an empty string.
> 
> Fixes: bf1fa1dae68e ("checkpatch: externalize the structs that should be const")

Probably not worthy of a Fixes: line, as that's
generally used for backporting, but OK by me.

> diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
[]
> @@ -781,8 +781,10 @@ sub read_words {
>  }
>  
>  my $const_structs = "";

This might be a tiny bit faster/less cpu using:

my $const_structs;

> -read_words(\$const_structs, $conststructsfile)
> -    or warn "No structs that should be const will be found - file '$conststructsfile': $!\n";
> +if (show_type("CONST_STRUCT")) {
> +	read_words(\$const_structs, $conststructsfile)
> +	    or warn "No structs that should be const will be found - file '$conststructsfile': $!\n";
> +}
>  
>  my $typeOtherTypedefs = "";
>  if (length($typedefsfile)) {
> @@ -6660,7 +6662,8 @@ sub process {
>  
>  # check for various structs that are normally const (ops, kgdb, device_tree)
>  # and avoid what seem like struct definitions 'struct foo {'
> -		if ($line !~ /\bconst\b/ &&
> +		if ($const_structs ne "" &&

instead testing

		if (defined($const_structs) &&

> +		    $line !~ /\bconst\b/ &&
>  		    $line =~ /\bstruct\s+($const_structs)\b(?!\s*\{)/) {
>  			WARN("CONST_STRUCT",
>  			     "struct $1 should normally be const\n" . $herecurr);