checkpatch: add tests for function pointer style misuses

Kernel style uses function pointers in this form:
	"type (*funcptr)(args...)"

Emit warnings when this function pointer form isn't used.

Signed-off-by: Joe Perches <joe@perches.com>
Cc: Andy Whitcroft <apw@shadowen.org>
Cc: Derek Perrin <d.roc16@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

scripts/checkpatch.pl

@@ -2811,6 +2811,65 @@ sub process {
 			}
 		}
 
+# Function pointer declarations
+# check spacing between type, funcptr, and args
+# canonical declaration is "type (*funcptr)(args...)"
+#
+# the $Declare variable will capture all spaces after the type
+# so check it for trailing missing spaces or multiple spaces
+		if ($line =~ /^.\s*($Declare)\((\s*)\*(\s*)$Ident(\s*)\)(\s*)\(/) {
+			my $declare = $1;
+			my $pre_pointer_space = $2;
+			my $post_pointer_space = $3;
+			my $funcname = $4;
+			my $post_funcname_space = $5;
+			my $pre_args_space = $6;
+
+			if ($declare !~ /\s$/) {
+				WARN("SPACING",
+				     "missing space after return type\n" . $herecurr);
+			}
+
+# unnecessary space "type  (*funcptr)(args...)"
+			elsif ($declare =~ /\s{2,}$/) {
+				WARN("SPACING",
+				     "Multiple spaces after return type\n" . $herecurr);
+			}
+
+# unnecessary space "type ( *funcptr)(args...)"
+			if (defined $pre_pointer_space &&
+			    $pre_pointer_space =~ /^\s/) {
+				WARN("SPACING",
+				     "Unnecessary space after function pointer open parenthesis\n" . $herecurr);
+			}
+
+# unnecessary space "type (* funcptr)(args...)"
+			if (defined $post_pointer_space &&
+			    $post_pointer_space =~ /^\s/) {
+				WARN("SPACING",
+				     "Unnecessary space before function pointer name\n" . $herecurr);
+			}
+
+# unnecessary space "type (*funcptr )(args...)"
+			if (defined $post_funcname_space &&
+			    $post_funcname_space =~ /^\s/) {
+				WARN("SPACING",
+				     "Unnecessary space after function pointer name\n" . $herecurr);
+			}
+
+# unnecessary space "type (*funcptr) (args...)"
+			if (defined $pre_args_space &&
+			    $pre_args_space =~ /^\s/) {
+				WARN("SPACING",
+				     "Unnecessary space before function pointer arguments\n" . $herecurr);
+			}
+
+			if (show_type("SPACING") && $fix) {
+				$fixed[$linenr - 1] =~
+				    s/^(.\s*$Declare)\(\s*\*\s*($Ident)\s*\)\s*\(/rtrim($1) . " " . "\(\*$2\)\("/ex;
+			}
+		}
+
 # check for spacing round square brackets; allowed:
 #  1. with a type on the left -- int [] a;
 #  2. at the beginning of a line for slice initialisers -- [0...10] = 5,