Merge tag 'cocci-7.0-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/jlawall/linux

Pull coccinelle updates from Julia Lawall:
 "This simplifies and clarifies the handling of output generated by
  Coccinelle that is sent to standard error.

  By default, this goes to /dev/null. Remind the user of that and
  encourage them to provide another file name (Benjamin Philip)"

* tag 'cocci-7.0-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/jlawall/linux:
  Documentation: Coccinelle: document debug log handling
  scripts: coccicheck: warn on unset debug file
  scripts: coccicheck: simplify debug file handling

2 files changed, 29 insertions, 13 deletions

diff --git a/Documentation/dev-tools/coccinelle.rst b/Documentation/dev-tools/coccinelle.rst
index 6e70a1e9a3c0..c714780d458a 100644
--- a/Documentation/dev-tools/coccinelle.rst
+++ b/Documentation/dev-tools/coccinelle.rst
@@ -127,6 +127,18 @@ To enable verbose messages set the V= variable, for example::
 
    make coccicheck MODE=report V=1
 
+By default, coccicheck will print debug logs to stdout and redirect stderr to
+/dev/null. This can make coccicheck output difficult to read and understand.
+Debug and error messages can instead be written to a debug file instead by
+setting the ``DEBUG_FILE`` variable::
+
+    make coccicheck MODE=report DEBUG_FILE="cocci.log"
+
+Coccinelle cannot overwrite a debug file. Instead of repeatedly deleting a log
+file, you could include the datetime in the debug file name::
+
+    make coccicheck MODE=report DEBUG_FILE="cocci-$(date -Iseconds).log"
+
 Coccinelle parallelization
 --------------------------
 
@@ -208,11 +220,10 @@ include options matching the options used when we compile the kernel.
 You can learn what these options are by using V=1; you could then
 manually run Coccinelle with debug options added.
 
-Alternatively you can debug running Coccinelle against SmPL patches
-by asking for stderr to be redirected to stderr. By default stderr
-is redirected to /dev/null; if you'd like to capture stderr you
-can specify the ``DEBUG_FILE="file.txt"`` option to coccicheck. For
-instance::
+An easier approach to debug running Coccinelle against SmPL patches is to ask
+coccicheck to redirect stderr to a debug file. As mentioned in the examples, by
+default stderr is redirected to /dev/null; if you'd like to capture stderr you
+can specify the ``DEBUG_FILE="file.txt"`` option to coccicheck. For instance::
 
     rm -f cocci.err
     make coccicheck COCCI=scripts/coccinelle/free/kfree.cocci MODE=report DEBUG_FILE=cocci.err
diff --git a/scripts/coccicheck b/scripts/coccicheck
index 89d591af5f3e..8dd766009de1 100755
--- a/scripts/coccicheck
+++ b/scripts/coccicheck
@@ -138,7 +138,7 @@ run_cmd_parmap() {
 	if [ $VERBOSE -ne 0 ] ; then
 		echo "Running ($NPROC in parallel): $@"
 	fi
-	if [ "$DEBUG_FILE" != "/dev/null" -a "$DEBUG_FILE" != "" ]; then
+	if [ "$DEBUG_FILE" != "/dev/null" ]; then
                 echo $@>>$DEBUG_FILE
                 $@ 2>>$DEBUG_FILE
         else
@@ -259,13 +259,18 @@ coccinelle () {
 
 }
 
-if [ "$DEBUG_FILE" != "/dev/null" -a "$DEBUG_FILE" != "" ]; then
-	if [ -f $DEBUG_FILE ]; then
-		echo "Debug file $DEBUG_FILE exists, bailing"
-		exit
-	fi
-else
-	DEBUG_FILE="/dev/null"
+if [ "$DEBUG_FILE" = "" ]; then
+    echo 'You have not explicitly specified the debug file to use.'
+    echo 'Using default "/dev/null" as debug file.'
+    echo 'Debug logs will be printed to stdout.'
+    echo 'You can specify the debug file with "make coccicheck DEBUG_FILE=<debug_file>"'
+    echo ''
+    DEBUG_FILE="/dev/null"
+fi
+
+if [ -f $DEBUG_FILE ]; then
+	echo "Debug file $DEBUG_FILE exists, bailing"
+	exit
 fi
 
 if [ "$COCCI" = "" ] ; then