[PATCH v2 3/3] fs/locks: Use fs-specific l_pid for remote locks

[Benjamin Coddington <bcodding@xxxxxxxxxx>]

Now that we're setting fl_nspid at file_lock allocation, we need to handle
the case where a remote filesystem directly sets fl_pid.  If the filesystem
implements the lock operation, set a flag to return the lock's fl_pid,
rather than fl_nspid.

Signed-off-by: Benjamin Coddington <bcodding@xxxxxxxxxx>
---
 fs/locks.c         | 25 +++++++++++++++++++------
 include/linux/fs.h |  7 +++++++
 2 files changed, 26 insertions(+), 6 deletions(-)

diff --git a/fs/locks.c b/fs/locks.c
index 0f5a461b8da6..c7a222a8eaa7 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -2047,16 +2047,28 @@ SYSCALL_DEFINE2(flock, unsigned int, fd, unsigned int, cmd)
  */
 int vfs_test_lock(struct file *filp, struct file_lock *fl)
 {
-	if (filp->f_op->lock && is_remote_lock(filp))
+	if (filp->f_op->lock && is_remote_lock(filp)) {
+		fl->fl_flags |= FL_PID_PRIV;
 		return filp->f_op->lock(filp, F_GETLK, fl);
+	}
 	posix_test_lock(filp, fl);
 	return 0;
 }
 EXPORT_SYMBOL_GPL(vfs_test_lock);
 
+static inline int flock_translate_pid(struct file_lock *fl)
+{
+	if (IS_OFDLCK(fl))
+		return -1;
+	if (fl->fl_flags & FL_PID_PRIV)
+		return fl->fl_pid;
+	return pid_vnr(fl->fl_nspid);
+}
+
+
 static int posix_lock_to_flock(struct flock *flock, struct file_lock *fl)
 {
-	flock->l_pid = IS_OFDLCK(fl) ? -1 : fl->fl_pid;
+	flock->l_pid = flock_translate_pid(fl);
 #if BITS_PER_LONG == 32
 	/*
 	 * Make sure we can represent the posix lock via
@@ -2078,7 +2090,7 @@ static int posix_lock_to_flock(struct flock *flock, struct file_lock *fl)
 #if BITS_PER_LONG == 32
 static void posix_lock_to_flock64(struct flock64 *flock, struct file_lock *fl)
 {
-	flock->l_pid = IS_OFDLCK(fl) ? -1 : fl->fl_pid;
+	flock->l_pid = flock_translate_pid(fl);
 	flock->l_start = fl->fl_start;
 	flock->l_len = fl->fl_end == OFFSET_MAX ? 0 :
 		fl->fl_end - fl->fl_start + 1;
@@ -2596,7 +2608,9 @@ static void lock_get_status(struct seq_file *f, struct file_lock *fl,
 	struct inode *inode = NULL;
 	unsigned int fl_pid;
 
-	if (fl->fl_nspid) {
+	if (fl->fl_flags & FL_PID_PRIV) {
+		fl_pid = fl->fl_pid;
+	} else {
 		struct pid_namespace *proc_pidns = file_inode(f->file)->i_sb->s_fs_info;
 
 		/* Don't let fl_pid change based on who is reading the file */
@@ -2609,8 +2623,7 @@ static void lock_get_status(struct seq_file *f, struct file_lock *fl,
 		 */
 		if (fl_pid == 0)
 			return;
-	} else
-		fl_pid = fl->fl_pid;
+	}
 
 	if (fl->fl_file != NULL)
 		inode = locks_inode(fl->fl_file);
diff --git a/include/linux/fs.h b/include/linux/fs.h
index aa4affb38c39..11794cbaaed0 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -908,6 +908,7 @@ static inline struct file *get_file(struct file *f)
 #define FL_UNLOCK_PENDING	512 /* Lease is being broken */
 #define FL_OFDLCK	1024	/* lock is "owned" by struct file */
 #define FL_LAYOUT	2048	/* outstanding pNFS layout */
+#define FL_PID_PRIV	4096	/* F_GETLK should report fl_pid */
 
 #define FL_CLOSE_POSIX (FL_POSIX | FL_CLOSE)
 
@@ -973,6 +974,12 @@ int opens_in_grace(struct net *);
  * 3) lock range end
  *
  * Obviously, the last two criteria only matter for POSIX locks.
+ *
+ * fl_pid and fl_nspid appear redundant, but fl_pid is used to handle cases
+ * where a local F_GETLK returns a lock that was granted to a remote owner,
+ * as might exist with a remotely available filesystem like NFS.  For that
+ * case, the lock manager should set fl_pid, and that value is returned to a
+ * local F_GETLK.
  */
 struct file_lock {
 	struct file_lock *fl_next;	/* singly linked list for this inode  */
-- 
2.9.3