[Qemu-devel] [PATCH 2/4] CODING_STYLE, checkpatch: update line length rules

[Paolo Bonzini <pbonzini@redhat.com>]

Line lengths above 80 characters do exist.  They are rare, but
they happen from time to time.  An ignored rule is worse than an
exception to the rule, so do the latter.

Based on remarks from the list, make the preferred line length
slightly lower than 80 characters, to account for extra characters
in unified diffs (including three-way diffs) and for email quoting.

Checkpatch has some code to detect doc comments that doesn't apply
to QEMU; the usual limits apply even for doc comments in our case.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 CODING_STYLE          | 13 ++++++++++---
 scripts/checkpatch.pl | 21 +++++++++++++++------
 2 files changed, 25 insertions(+), 9 deletions(-)

diff --git a/CODING_STYLE b/CODING_STYLE
index 3c6978f..34d5526 100644
--- a/CODING_STYLE
+++ b/CODING_STYLE
@@ -31,14 +31,21 @@ Do not leave whitespace dangling off the ends of lines.
 
 2. Line width
 
-Lines are 80 characters; not longer.
+Lines should be 76 characters; try not to make them longer.
+
+Sometimes it is hard to do, especially when dealing with QEMU subsystems
+that use long function or symbol names.  Even in that case, do not make
+lines much longer than 76 characters.
 
 Rationale:
  - Some people like to tile their 24" screens with a 6x4 matrix of 80x24
-   xterms and use vi in all of them.  The best way to punish them is to
-   let them keep doing it.
+   xterms and use vi in all of them.  They also examine diffs (and three-way
+   diffs) on an 80-column terminal, accounting for two extra characters.
+   The best way to punish them is to let them keep doing it.
  - Code and especially patches is much more readable if limited to a sane
    line length.  Eighty is traditional.
+ - The four-space indentation makes the most common excuse ("But look
+   at all that white space on the left!") moot.
  - It is the QEMU coding style.
 
 3. Naming
diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 7f0aae9..bc32d8f 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -1466,14 +1466,23 @@ sub process {
 # check we are in a valid source file if not then ignore this hunk
 		next if ($realfile !~ /\.(h|c|cpp|s|S|pl|sh)$/);
 
-#80 column limit
-		if ($line =~ /^\+/ && $prevrawline !~ /\/\*\*/ &&
-		    $rawline !~ /^.\s*\*\s*\@$Ident\s/ &&
+#90 column limit
+		if ($line =~ /^\+/ &&
 		    !($line =~ /^\+\s*$logFunctions\s*\(\s*(?:(KERN_\S+\s*|[^"]*))?"[X\t]*"\s*(?:,|\)\s*;)\s*$/ ||
-		    $line =~ /^\+\s*"[^"]*"\s*(?:\s*|,|\)\s*;)\s*$/) &&
-		    $length > 80)
+		    !($line =~ /^\+\s*"[^"]*"\s*(?:\s*|,|\)\s*;)\s*$/))
 		{
-			WARN("line over 80 characters\n" . $herecurr);
+			if ($length > 90) {
+				ERROR("line over 90 characters\n" . $herecurr);
+			} elsif ($length > 76 && !($rawline =~ /^\+ \* /)) {
+				# The BSD license blurb has 80 character lines.
+				# Avoid warning on cut-and-pasted license text.
+				WARN("line over 76 characters\n" . $herecurr);
+			} elsif ($length > 80) {
+				# Do not confuse the user by introducing yet
+				# another limit (80 characters).  Technically,
+				# this line *is* over 76 characters.
+				WARN("line over 76 characters\n" . $herecurr);
+			}
 		}
 
 # check for spaces before a quoted newline
-- 
2.4.3