Wire up the userspace interface for write stream management via three
new fcntls.
F_GET_MAX_WRITE_STREAMS: Returns the number of available streams.
F_SET_WRITE_STREAM: Assign a specific stream value to the file.
F_GET_WRITE_STREAM: Query what stream value is set on the file.

Application should query the available streams by calling
F_GET_MAX_WRITE_STREAMS first.
If returned value is N, valid stream values for the file are 0 to N.
Stream value 0 implies that no stream is set on the file.
Setting a larger value than available streams is rejected.

Signed-off-by: Kanchan Joshi <joshi.k@samsung.com>
---
 fs/fcntl.c                 | 33 +++++++++++++++++++++++++++++++++
 include/uapi/linux/fcntl.h |  4 ++++
 2 files changed, 37 insertions(+)

diff --git a/fs/fcntl.c b/fs/fcntl.c
index f93dbca08435..c982f0506a3f 100644
--- a/fs/fcntl.c
+++ b/fs/fcntl.c
@@ -441,6 +441,30 @@ static int f_owner_sig(struct file *filp, int signum, bool setsig)
 	return ret;
 }
 
+static long fcntl_get_max_write_streams(struct file *filp)
+{
+	if (filp->f_op->get_max_write_streams)
+		return filp->f_op->get_max_write_streams(filp);
+
+	return -EOPNOTSUPP;
+}
+
+static long fcntl_set_write_stream(struct file *filp, unsigned long arg)
+{
+	if (filp->f_op->set_write_stream)
+		return filp->f_op->set_write_stream(filp, arg);
+
+	return -EOPNOTSUPP;
+}
+
+static long fcntl_get_write_stream(struct file *filp)
+{
+	if (filp->f_op->get_write_stream)
+		return filp->f_op->get_write_stream(filp);
+
+	return -EOPNOTSUPP;
+}
+
 static long do_fcntl(int fd, unsigned int cmd, unsigned long arg,
 		struct file *filp)
 {
@@ -563,6 +587,15 @@ static long do_fcntl(int fd, unsigned int cmd, unsigned long arg,
 			return -EFAULT;
 		err = fcntl_setdeleg(fd, filp, &deleg);
 		break;
+	case F_GET_MAX_WRITE_STREAMS:
+		err = fcntl_get_max_write_streams(filp);
+		break;
+	case F_SET_WRITE_STREAM:
+		err = fcntl_set_write_stream(filp, arg);
+		break;
+	case F_GET_WRITE_STREAM:
+		err = fcntl_get_write_stream(filp);
+		break;
 	default:
 		break;
 	}
diff --git a/include/uapi/linux/fcntl.h b/include/uapi/linux/fcntl.h
index aadfbf6e0cb3..4b75470fc07a 100644
--- a/include/uapi/linux/fcntl.h
+++ b/include/uapi/linux/fcntl.h
@@ -190,4 +190,8 @@ struct delegation {
 #define AT_EXECVE_CHECK		0x10000	/* Only perform a check if execution
 					   would be allowed. */
 
+/* write stream management */
+#define F_GET_MAX_WRITE_STREAMS		(F_LINUX_SPECIFIC_BASE + 17)
+#define F_GET_WRITE_STREAM		(F_LINUX_SPECIFIC_BASE + 18)
+#define F_SET_WRITE_STREAM		(F_LINUX_SPECIFIC_BASE + 19)
 #endif /* _UAPI_LINUX_FCNTL_H */
-- 
2.25.1