[PATCH v6 05/20] fs: Restore F_[GS]ET_FILE_RW_HINT support

[Bart Van Assche <bvanassche@acm.org>]

Since there are applications (e.g. Ceph) that use F_[GS]ET_FILE_RW_HINT,
restore support for these fcntls. This patch restores functionality that
was removed by commit 7b12e49669c9 ("fs: remove fs.f_write_hint").

Cc: Jeff Layton <jlayton@kernel.org>
Cc: Chuck Lever <chuck.lever@oracle.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Dave Chinner <dchinner@redhat.com>
Cc: Chaitanya Kulkarni <kch@nvidia.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
 fs/fcntl.c         | 37 +++++++++++++++++++++++++++++++++++++
 fs/open.c          |  1 +
 include/linux/fs.h |  9 +++++++++
 3 files changed, 47 insertions(+)

diff --git a/fs/fcntl.c b/fs/fcntl.c
index fc73c5fae43c..8018c4da478c 100644
--- a/fs/fcntl.c
+++ b/fs/fcntl.c
@@ -322,6 +322,37 @@ static long fcntl_set_rw_hint(struct file *file, unsigned int cmd,
 	return 0;
 }
 
+static long fcntl_get_file_rw_hint(struct file *file, unsigned int cmd,
+				   unsigned long arg)
+{
+	struct inode *inode = file_inode(file);
+	u64 __user *argp = (u64 __user *)arg;
+	u64 hint = inode->i_write_hint;
+
+	hint = file_write_hint(file);
+	if (copy_to_user(argp, &hint, sizeof(*argp)))
+		return -EFAULT;
+	return 0;
+}
+
+static long fcntl_set_file_rw_hint(struct file *file, unsigned int cmd,
+				   unsigned long arg)
+{
+	u64 __user *argp = (u64 __user *)arg;
+	u64 hint;
+
+	if (copy_from_user(&hint, argp, sizeof(hint)))
+		return -EFAULT;
+	if (!rw_hint_valid(hint))
+		return -EINVAL;
+
+	spin_lock(&file->f_lock);
+	file->f_write_hint = hint;
+	spin_unlock(&file->f_lock);
+
+	return 0;
+}
+
 static long do_fcntl(int fd, unsigned int cmd, unsigned long arg,
 		struct file *filp)
 {
@@ -430,6 +461,12 @@ static long do_fcntl(int fd, unsigned int cmd, unsigned long arg,
 	case F_SET_RW_HINT:
 		err = fcntl_set_rw_hint(filp, cmd, arg);
 		break;
+	case F_GET_FILE_RW_HINT:
+		err = fcntl_get_file_rw_hint(filp, cmd, arg);
+		break;
+	case F_SET_FILE_RW_HINT:
+		err = fcntl_set_file_rw_hint(filp, cmd, arg);
+		break;
 	default:
 		break;
 	}
diff --git a/fs/open.c b/fs/open.c
index 02dc608d40d8..4c5c29541ac5 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -961,6 +961,7 @@ static int do_dentry_open(struct file *f,
 	if (f->f_mapping->a_ops && f->f_mapping->a_ops->direct_IO)
 		f->f_mode |= FMODE_CAN_ODIRECT;
 
+	f->f_write_hint = WRITE_LIFE_NOT_SET;
 	f->f_flags &= ~(O_CREAT | O_EXCL | O_NOCTTY | O_TRUNC);
 	f->f_iocb_flags = iocb_flags(f);
 
diff --git a/include/linux/fs.h b/include/linux/fs.h
index a08014b68d6e..a6e0c4b5a72b 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -989,6 +989,7 @@ struct file {
 	 * Must not be taken from IRQ context.
 	 */
 	spinlock_t		f_lock;
+	enum rw_hint		f_write_hint;
 	fmode_t			f_mode;
 	atomic_long_t		f_count;
 	struct mutex		f_pos_lock;
@@ -2162,6 +2163,14 @@ static inline bool HAS_UNMAPPED_ID(struct mnt_idmap *idmap,
 	       !vfsgid_valid(i_gid_into_vfsgid(idmap, inode));
 }
 
+static inline enum rw_hint file_write_hint(struct file *file)
+{
+	if (file->f_write_hint != WRITE_LIFE_NOT_SET)
+		return file->f_write_hint;
+
+	return file_inode(file)->i_write_hint;
+}
+
 static inline void init_sync_kiocb(struct kiocb *kiocb, struct file *filp)
 {
 	*kiocb = (struct kiocb) {