[RFC PATCH 4/5] locks: handle merging of locks when FL_FILP_PRIVATE is set

[Jeff Layton <jlayton@redhat.com>]

Since FL_FILP_PRIVATE locks have different semantics on close, we can't
merge them with "normal" locks or with other FL_FILP_PRIVATE locks that
were acquired on different file descriptors. Consolidate the logic that
determines this into its own function.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
---
 fs/locks.c | 38 +++++++++++++++++++++++++++++++++++---
 1 file changed, 35 insertions(+), 3 deletions(-)

diff --git a/fs/locks.c b/fs/locks.c
index 7186b9a..3bde157 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -934,6 +934,39 @@ out:
 	return error;
 }
 
+/**
+ * posix_locks_mergeable - are two posix locks able to be merged?
+ * @fl1: first posix lock
+ * @fl2: second posix lock
+ *
+ * Determine whether two posix locks are potentially able to be merged. If
+ * they are of different types or have different settings of FL_FILP_PRIVATE
+ * then they cannot be. Ditto if they are FL_FILP_PRIVATE locks and are
+ * associated with different file descriptors.
+ */
+static bool
+posix_locks_mergeable(struct file_lock *fl1, struct file_lock *fl2)
+{
+	unsigned int p1, p2;
+
+	/* Different types are not mergeable */
+	if (fl1->fl_type != fl2->fl_type)
+		return false;
+
+	p1 = IS_PRIVATE(fl1);
+	p2 = IS_PRIVATE(fl2);
+
+	/* Different settings of FL_FILP_PRIVATE aren't mergeable */
+	if (p1 != p2)
+		return false;
+
+	/* When FL_FILP_PRIVATE is set, fl_file must be same */
+	if (p1 && fl1->fl_file != fl2->fl_file)
+		return false;
+
+	return true;
+}
+
 static int __posix_lock_file(struct inode *inode, struct file_lock *request, struct file_lock *conflock)
 {
 	struct file_lock *fl;
@@ -1018,9 +1051,8 @@ static int __posix_lock_file(struct inode *inode, struct file_lock *request, str
 		     request->fl_file != fl->fl_file)
 			goto next_lock;
 
-		/* Detect adjacent or overlapping regions (if same lock type)
-		 */
-		if (request->fl_type == fl->fl_type) {
+		/* Detect adjacent or overlapping regions (if same lock type) */
+		if (posix_locks_mergeable(fl, request)) {
 			/* In all comparisons of start vs end, use
 			 * "start - 1" rather than "end + 1". If end
 			 * is OFFSET_MAX, end + 1 will become negative.
-- 
1.8.3.1