[PATCH for-next 3/4] io_uring: grow a field in struct io_uring_cmd

[Kanchan Joshi]

Use the leftover space to carve 'next' field that enables linking of
io_uring_cmd structs. Also introduce a list head and few helpers.

This is in preparation to support nvme-mulitpath, allowing multiple
uring passthrough commands to be queued.

Signed-off-by: Kanchan Joshi <joshi.k at samsung.com>
Signed-off-by: Anuj Gupta <anuj20.g at samsung.com>
---
 include/linux/io_uring.h | 38 ++++++++++++++++++++++++++++++++++++--
 1 file changed, 36 insertions(+), 2 deletions(-)

diff --git a/include/linux/io_uring.h b/include/linux/io_uring.h
index 54063d67506b..d734599cbcd7 100644
--- a/include/linux/io_uring.h
+++ b/include/linux/io_uring.h
@@ -22,9 +22,14 @@ struct io_uring_cmd {
 	const void	*cmd;
 	/* callback to defer completions to task context */
 	void (*task_work_cb)(struct io_uring_cmd *cmd);
+	struct io_uring_cmd	*next;
 	u32		cmd_op;
-	u32		pad;
-	u8		pdu[32]; /* available inline for free use */
+	u8		pdu[28]; /* available inline for free use */
+};
+
+struct ioucmd_list {
+	struct io_uring_cmd *head;
+	struct io_uring_cmd *tail;
 };
 
 #if defined(CONFIG_IO_URING)
@@ -54,6 +59,27 @@ static inline void io_uring_free(struct task_struct *tsk)
 	if (tsk->io_uring)
 		__io_uring_free(tsk);
 }
+
+static inline struct io_uring_cmd *ioucmd_list_get(struct ioucmd_list *il)
+{
+	struct io_uring_cmd *ioucmd = il->head;
+
+	il->head = il->tail = NULL;
+
+	return ioucmd;
+}
+
+static inline void ioucmd_list_add(struct ioucmd_list *il,
+		struct io_uring_cmd *ioucmd)
+{
+	ioucmd->next = NULL;
+
+	if (il->tail)
+		il->tail->next = ioucmd;
+	else
+		il->head = ioucmd;
+	il->tail = ioucmd;
+}
 #else
 static inline void io_uring_cmd_done(struct io_uring_cmd *cmd, ssize_t ret,
 		ssize_t ret2)
@@ -80,6 +106,14 @@ static inline const char *io_uring_get_opcode(u8 opcode)
 {
 	return "";
 }
+static inline struct io_uring_cmd *ioucmd_list_get(struct ioucmd_list *il)
+{
+	return NULL;
+}
+static inline void ioucmd_list_add(struct ioucmd_list *il,
+		struct io_uring_cmd *ioucmd)
+{
+}
 #endif
 
 #endif
-- 
2.25.1