block: Add FIFO scheduler

Signed-off-by: andip71 <andreasp@gmx.de>
Signed-off-by: djb77 <dwayne.bakewell@gmail.com>
Signed-off-by: prashantpaddune <elonpras@my.smccd.edu>

arch/arm64/configs/exynos7885-a7y18lte_defconfig

@@ -310,11 +310,13 @@ CONFIG_IOSCHED_BFQ=y
 # CONFIG_BFQ_GROUP_IOSCHED is not set
 CONFIG_IOSCHED_FIOPS=y
 CONFIG_IOSCHED_SIO=y
+CONFIG_IOSCHED_FIFO=y
 CONFIG_DEFAULT_CFQ=y
 # CONFIG_DEFAULT_BFQ is not set
 # CONFIG_DEFAULT_NOOP is not set
 # CONFIG_DEFAULT_FIOPS is not set
 # CONFIG_DEFAULT_SIO is not set
+# CONFIG_DEFAULT_FIFO is not set
 CONFIG_DEFAULT_IOSCHED="cfq"
 CONFIG_ASN1=y
 CONFIG_UNINLINE_SPIN_UNLOCK=y

block/Kconfig.iosched

@@ -76,6 +76,13 @@ config IOSCHED_FIOPS
           IOPS equally among all processes in the system. It's mainly for
           Flash based storage.
 
+config IOSCHED_FIFO
+	tristate "FIFO I/O scheduler"
+	default y
+	---help---
+	  Fifo is similar to no-op I/O scheduler and it's a minimal scheduler that does basic merging
+	  and sorting. Ported from: https://github.com/AndroidDeveloperAlliance/ZenKernel_TUNA/blob/master/block/fifo-iosched.c
+
 choice
 	prompt "Default I/O scheduler"
 	default DEFAULT_CFQ
@@ -108,6 +115,9 @@ choice
 	config DEFAULT_SIO
 		bool "SIO" if IOSCHED_SIO=y
 
+	config DEFAULT_FIFO
+		bool "fifo" if IOSCHED_FIFO=y
+
 endchoice
 
 config DEFAULT_IOSCHED
@@ -118,6 +128,7 @@ config DEFAULT_IOSCHED
 	default "fiops" if DEFAULT_FIOPS
 	default "noop" if DEFAULT_NOOP
 	default "sio" if DEFAULT_SIO
+	default "fifo" if DEFAULT_FIFO
 
 endmenu
 

block/Makefile

@@ -21,6 +21,7 @@ obj-$(CONFIG_IOSCHED_CFQ)	+= cfq-iosched.o
 obj-$(CONFIG_IOSCHED_BFQ)	+= bfq-iosched.o
 obj-$(CONFIG_IOSCHED_FIOPS)	+= fiops-iosched.o
 obj-$(CONFIG_IOSCHED_SIO)	+= sio-iosched.o
+obj-$(CONFIG_IOSCHED_FIFO)	+= fifo-iosched.o
 
 obj-$(CONFIG_BLOCK_COMPAT)	+= compat_ioctl.o
 obj-$(CONFIG_BLK_CMDLINE_PARSER)	+= cmdline-parser.o

block/fifo-iosched.c

@@ -0,0 +1,99 @@
+/*
+ * FIFO I/O scheduler (_really_ does no-op)
+ */
+#include <linux/blkdev.h>
+#include <linux/elevator.h>
+#include <linux/bio.h>
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+
+struct fifo_data {
+	struct list_head queue;
+};
+
+static int fifo_dispatch(struct request_queue *q, int force)
+{
+	struct fifo_data *fifo_d = q->elevator->elevator_data;
+
+	if (!list_empty(&fifo_d->queue)) {
+		struct request *req = list_entry(fifo_d->queue.next, struct request, queuelist);
+		list_del_init(&req->queuelist);
+		elv_dispatch_add_tail(q, req);
+		return 1;
+	}
+	return 0;
+}
+
+static void fifo_add_request(struct request_queue *q, struct request *req)
+{
+	struct fifo_data *fifo_d = q->elevator->elevator_data;
+	list_add_tail(&req->queuelist, &fifo_d->queue);
+}
+
+static int fifo_init_queue(struct request_queue *q, struct elevator_type *e)
+{
+	struct fifo_data *fifo_d;
+	struct elevator_queue *eq;
+
+	eq = elevator_alloc(q, e);
+	if (!eq)
+		return -ENOMEM;
+
+	fifo_d = kmalloc_node(sizeof(*fifo_d), GFP_KERNEL, q->node);
+	if (!fifo_d) {
+		kobject_put(&eq->kobj);
+		return -ENOMEM;
+	}
+	eq->elevator_data = fifo_d;
+
+	INIT_LIST_HEAD(&fifo_d->queue);
+
+	spin_lock_irq(q->queue_lock);
+	q->elevator = eq;
+	spin_unlock_irq(q->queue_lock);
+	return 0;
+}
+
+static void fifo_exit_queue(struct elevator_queue *e)
+{
+        struct fifo_data *fifo_d = e->elevator_data;
+
+        BUG_ON(!list_empty(&fifo_d->queue));
+        kfree(fifo_d);
+}
+
+static int fifo_deny_merge(struct request_queue *req_q, struct request *req,
+			struct bio *bio)
+{
+	return ELEVATOR_NO_MERGE;
+}
+
+static struct elevator_type elevator_fifo = {
+	.ops = {
+		.elevator_dispatch_fn		= fifo_dispatch,
+		.elevator_add_req_fn		= fifo_add_request,
+		.elevator_allow_merge_fn 	= fifo_deny_merge,
+		.elevator_init_fn		= fifo_init_queue,
+		.elevator_exit_fn		= fifo_exit_queue,
+	},
+	.elevator_name = "fifo",
+	.elevator_owner = THIS_MODULE,
+};
+
+static int __init fifo_init(void)
+{
+	return elv_register(&elevator_fifo);
+}
+
+static void __exit fifo_exit(void)
+{
+	elv_unregister(&elevator_fifo);
+}
+
+module_init(fifo_init);
+module_exit(fifo_exit);
+
+MODULE_AUTHOR("Aaron Carroll");
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("No-op IO scheduler that actually does nothing");