1 files changed, 243 insertions, 0 deletions
diff --git a/block/blk-ioprio.c b/block/blk-ioprio.c
new file mode 100644
index 000000000000..4051fada01f1
--- /dev/null
+++ b/block/blk-ioprio.c
@@ -0,0 +1,243 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Block rq-qos policy for assigning an I/O priority class to requests.
+ *
+ * Using an rq-qos policy for assigning I/O priority class has two advantages
+ * over using the ioprio_set() system call:
+ *
+ * - This policy is cgroup based so it has all the advantages of cgroups.
+ * - While ioprio_set() does not affect page cache writeback I/O, this rq-qos
+ *   controller affects page cache writeback I/O for filesystems that support
+ *   assiociating a cgroup with writeback I/O. See also
+ *   Documentation/admin-guide/cgroup-v2.rst.
+ */
+
+#include <linux/blk-mq.h>
+#include <linux/blk_types.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include "blk-cgroup.h"
+#include "blk-ioprio.h"
+#include "blk-rq-qos.h"
+
+/**
+ * enum prio_policy - I/O priority class policy.
+ * @POLICY_NO_CHANGE: (default) do not modify the I/O priority class.
+ * @POLICY_PROMOTE_TO_RT: modify no-IOPRIO_CLASS_RT to IOPRIO_CLASS_RT.
+ * @POLICY_RESTRICT_TO_BE: modify IOPRIO_CLASS_NONE and IOPRIO_CLASS_RT into
+ *		IOPRIO_CLASS_BE.
+ * @POLICY_ALL_TO_IDLE: change the I/O priority class into IOPRIO_CLASS_IDLE.
+ * @POLICY_NONE_TO_RT: an alias for POLICY_PROMOTE_TO_RT.
+ *
+ * See also <linux/ioprio.h>.
+ */
+enum prio_policy {
+	POLICY_NO_CHANGE	= 0,
+	POLICY_PROMOTE_TO_RT	= 1,
+	POLICY_RESTRICT_TO_BE	= 2,
+	POLICY_ALL_TO_IDLE	= 3,
+	POLICY_NONE_TO_RT	= 4,
+};
+
+static const char *policy_name[] = {
+	[POLICY_NO_CHANGE]	= "no-change",
+	[POLICY_PROMOTE_TO_RT]	= "promote-to-rt",
+	[POLICY_RESTRICT_TO_BE]	= "restrict-to-be",
+	[POLICY_ALL_TO_IDLE]	= "idle",
+	[POLICY_NONE_TO_RT]	= "none-to-rt",
+};
+
+static struct blkcg_policy ioprio_policy;
+
+/**
+ * struct ioprio_blkg - Per (cgroup, request queue) data.
+ * @pd: blkg_policy_data structure.
+ */
+struct ioprio_blkg {
+	struct blkg_policy_data pd;
+};
+
+/**
+ * struct ioprio_blkcg - Per cgroup data.
+ * @cpd: blkcg_policy_data structure.
+ * @prio_policy: One of the IOPRIO_CLASS_* values. See also <linux/ioprio.h>.
+ */
+struct ioprio_blkcg {
+	struct blkcg_policy_data cpd;
+	enum prio_policy	 prio_policy;
+};
+
+static inline struct ioprio_blkg *pd_to_ioprio(struct blkg_policy_data *pd)
+{
+	return pd ? container_of(pd, struct ioprio_blkg, pd) : NULL;
+}
+
+static struct ioprio_blkcg *blkcg_to_ioprio_blkcg(struct blkcg *blkcg)
+{
+	return container_of(blkcg_to_cpd(blkcg, &ioprio_policy),
+			    struct ioprio_blkcg, cpd);
+}
+
+static struct ioprio_blkcg *
+ioprio_blkcg_from_css(struct cgroup_subsys_state *css)
+{
+	return blkcg_to_ioprio_blkcg(css_to_blkcg(css));
+}
+
+static struct ioprio_blkcg *ioprio_blkcg_from_bio(struct bio *bio)
+{
+	struct blkg_policy_data *pd = blkg_to_pd(bio->bi_blkg, &ioprio_policy);
+
+	if (!pd)
+		return NULL;
+
+	return blkcg_to_ioprio_blkcg(pd->blkg->blkcg);
+}
+
+static int ioprio_show_prio_policy(struct seq_file *sf, void *v)
+{
+	struct ioprio_blkcg *blkcg = ioprio_blkcg_from_css(seq_css(sf));
+
+	seq_printf(sf, "%s\n", policy_name[blkcg->prio_policy]);
+	return 0;
+}
+
+static ssize_t ioprio_set_prio_policy(struct kernfs_open_file *of, char *buf,
+				      size_t nbytes, loff_t off)
+{
+	struct ioprio_blkcg *blkcg = ioprio_blkcg_from_css(of_css(of));
+	int ret;
+
+	if (off != 0)
+		return -EIO;
+	/* kernfs_fop_write_iter() terminates 'buf' with '\0'. */
+	ret = sysfs_match_string(policy_name, buf);
+	if (ret < 0)
+		return ret;
+	blkcg->prio_policy = ret;
+	return nbytes;
+}
+
+static struct blkg_policy_data *
+ioprio_alloc_pd(struct gendisk *disk, struct blkcg *blkcg, gfp_t gfp)
+{
+	struct ioprio_blkg *ioprio_blkg;
+
+	ioprio_blkg = kzalloc(sizeof(*ioprio_blkg), gfp);
+	if (!ioprio_blkg)
+		return NULL;
+
+	return &ioprio_blkg->pd;
+}
+
+static void ioprio_free_pd(struct blkg_policy_data *pd)
+{
+	struct ioprio_blkg *ioprio_blkg = pd_to_ioprio(pd);
+
+	kfree(ioprio_blkg);
+}
+
+static struct blkcg_policy_data *ioprio_alloc_cpd(gfp_t gfp)
+{
+	struct ioprio_blkcg *blkcg;
+
+	blkcg = kzalloc(sizeof(*blkcg), gfp);
+	if (!blkcg)
+		return NULL;
+	blkcg->prio_policy = POLICY_NO_CHANGE;
+	return &blkcg->cpd;
+}
+
+static void ioprio_free_cpd(struct blkcg_policy_data *cpd)
+{
+	struct ioprio_blkcg *blkcg = container_of(cpd, typeof(*blkcg), cpd);
+
+	kfree(blkcg);
+}
+
+#define IOPRIO_ATTRS						\
+	{							\
+		.name		= "prio.class",			\
+		.seq_show	= ioprio_show_prio_policy,	\
+		.write		= ioprio_set_prio_policy,	\
+	},							\
+	{ } /* sentinel */
+
+/* cgroup v2 attributes */
+static struct cftype ioprio_files[] = {
+	IOPRIO_ATTRS
+};
+
+/* cgroup v1 attributes */
+static struct cftype ioprio_legacy_files[] = {
+	IOPRIO_ATTRS
+};
+
+static struct blkcg_policy ioprio_policy = {
+	.dfl_cftypes	= ioprio_files,
+	.legacy_cftypes = ioprio_legacy_files,
+
+	.cpd_alloc_fn	= ioprio_alloc_cpd,
+	.cpd_free_fn	= ioprio_free_cpd,
+
+	.pd_alloc_fn	= ioprio_alloc_pd,
+	.pd_free_fn	= ioprio_free_pd,
+};
+
+void blkcg_set_ioprio(struct bio *bio)
+{
+	struct ioprio_blkcg *blkcg = ioprio_blkcg_from_bio(bio);
+	u16 prio;
+
+	if (!blkcg || blkcg->prio_policy == POLICY_NO_CHANGE)
+		return;
+
+	if (blkcg->prio_policy == POLICY_PROMOTE_TO_RT ||
+	    blkcg->prio_policy == POLICY_NONE_TO_RT) {
+		/*
+		 * For RT threads, the default priority level is 4 because
+		 * task_nice is 0. By promoting non-RT io-priority to RT-class
+		 * and default level 4, those requests that are already
+		 * RT-class but need a higher io-priority can use ioprio_set()
+		 * to achieve this.
+		 */
+		if (IOPRIO_PRIO_CLASS(bio->bi_ioprio) != IOPRIO_CLASS_RT)
+			bio->bi_ioprio = IOPRIO_PRIO_VALUE(IOPRIO_CLASS_RT, 4);
+		return;
+	}
+
+	/*
+	 * Except for IOPRIO_CLASS_NONE, higher I/O priority numbers
+	 * correspond to a lower priority. Hence, the max_t() below selects
+	 * the lower priority of bi_ioprio and the cgroup I/O priority class.
+	 * If the bio I/O priority equals IOPRIO_CLASS_NONE, the cgroup I/O
+	 * priority is assigned to the bio.
+	 */
+	prio = max_t(u16, bio->bi_ioprio,
+			IOPRIO_PRIO_VALUE(blkcg->prio_policy, 0));
+	if (prio > bio->bi_ioprio)
+		bio->bi_ioprio = prio;
+}
+
+void blk_ioprio_exit(struct gendisk *disk)
+{
+	blkcg_deactivate_policy(disk, &ioprio_policy);
+}
+
+int blk_ioprio_init(struct gendisk *disk)
+{
+	return blkcg_activate_policy(disk, &ioprio_policy);
+}
+
+static int __init ioprio_init(void)
+{
+	return blkcg_policy_register(&ioprio_policy);
+}
+
+static void __exit ioprio_exit(void)
+{
+	blkcg_policy_unregister(&ioprio_policy);
+}
+
+module_init(ioprio_init);
+module_exit(ioprio_exit);