1// SPDX-License-Identifier: GPL-2.0
  2/*
  3 * Block rq-qos policy for assigning an I/O priority class to requests.
  4 *
  5 * Using an rq-qos policy for assigning I/O priority class has two advantages
  6 * over using the ioprio_set() system call:
  7 *
  8 * - This policy is cgroup based so it has all the advantages of cgroups.
  9 * - While ioprio_set() does not affect page cache writeback I/O, this rq-qos
 10 *   controller affects page cache writeback I/O for filesystems that support
 11 *   assiociating a cgroup with writeback I/O. See also
 12 *   Documentation/admin-guide/cgroup-v2.rst.
 13 */
 14
 15#include <linux/blk-mq.h>
 16#include <linux/blk_types.h>
 17#include <linux/kernel.h>
 18#include <linux/module.h>
 19#include "blk-cgroup.h"
 20#include "blk-ioprio.h"
 21#include "blk-rq-qos.h"
 22
 23/**
 24 * enum prio_policy - I/O priority class policy.
 25 * @POLICY_NO_CHANGE: (default) do not modify the I/O priority class.
 26 * @POLICY_NONE_TO_RT: modify IOPRIO_CLASS_NONE into IOPRIO_CLASS_RT.
 27 * @POLICY_RESTRICT_TO_BE: modify IOPRIO_CLASS_NONE and IOPRIO_CLASS_RT into
 28 *		IOPRIO_CLASS_BE.
 29 * @POLICY_ALL_TO_IDLE: change the I/O priority class into IOPRIO_CLASS_IDLE.
 30 *
 31 * See also <linux/ioprio.h>.
 32 */
 33enum prio_policy {
 34	POLICY_NO_CHANGE	= 0,
 35	POLICY_NONE_TO_RT	= 1,
 36	POLICY_RESTRICT_TO_BE	= 2,
 37	POLICY_ALL_TO_IDLE	= 3,
 38};
 39
 40static const char *policy_name[] = {
 41	[POLICY_NO_CHANGE]	= "no-change",
 42	[POLICY_NONE_TO_RT]	= "none-to-rt",
 43	[POLICY_RESTRICT_TO_BE]	= "restrict-to-be",
 44	[POLICY_ALL_TO_IDLE]	= "idle",
 45};
 46
 47static struct blkcg_policy ioprio_policy;
 48
 49/**
 50 * struct ioprio_blkg - Per (cgroup, request queue) data.
 51 * @pd: blkg_policy_data structure.
 52 */
 53struct ioprio_blkg {
 54	struct blkg_policy_data pd;
 55};
 56
 57/**
 58 * struct ioprio_blkcg - Per cgroup data.
 59 * @cpd: blkcg_policy_data structure.
 60 * @prio_policy: One of the IOPRIO_CLASS_* values. See also <linux/ioprio.h>.
 61 */
 62struct ioprio_blkcg {
 63	struct blkcg_policy_data cpd;
 64	enum prio_policy	 prio_policy;
 65};
 66
 67static inline struct ioprio_blkg *pd_to_ioprio(struct blkg_policy_data *pd)
 68{
 69	return pd ? container_of(pd, struct ioprio_blkg, pd) : NULL;
 70}
 71
 72static struct ioprio_blkcg *blkcg_to_ioprio_blkcg(struct blkcg *blkcg)
 73{
 74	return container_of(blkcg_to_cpd(blkcg, &ioprio_policy),
 75			    struct ioprio_blkcg, cpd);
 76}
 77
 78static struct ioprio_blkcg *
 79ioprio_blkcg_from_css(struct cgroup_subsys_state *css)
 80{
 81	return blkcg_to_ioprio_blkcg(css_to_blkcg(css));
 82}
 83
 84static struct ioprio_blkcg *ioprio_blkcg_from_bio(struct bio *bio)
 85{
 86	struct blkg_policy_data *pd = blkg_to_pd(bio->bi_blkg, &ioprio_policy);
 87
 88	if (!pd)
 89		return NULL;
 90
 91	return blkcg_to_ioprio_blkcg(pd->blkg->blkcg);
 92}
 93
 94static int ioprio_show_prio_policy(struct seq_file *sf, void *v)
 95{
 96	struct ioprio_blkcg *blkcg = ioprio_blkcg_from_css(seq_css(sf));
 97
 98	seq_printf(sf, "%s\n", policy_name[blkcg->prio_policy]);
 99	return 0;
100}
101
102static ssize_t ioprio_set_prio_policy(struct kernfs_open_file *of, char *buf,
103				      size_t nbytes, loff_t off)
104{
105	struct ioprio_blkcg *blkcg = ioprio_blkcg_from_css(of_css(of));
106	int ret;
107
108	if (off != 0)
109		return -EIO;
110	/* kernfs_fop_write_iter() terminates 'buf' with '\0'. */
111	ret = sysfs_match_string(policy_name, buf);
112	if (ret < 0)
113		return ret;
114	blkcg->prio_policy = ret;
115	return nbytes;
116}
117
118static struct blkg_policy_data *
119ioprio_alloc_pd(gfp_t gfp, struct request_queue *q, struct blkcg *blkcg)
120{
121	struct ioprio_blkg *ioprio_blkg;
122
123	ioprio_blkg = kzalloc(sizeof(*ioprio_blkg), gfp);
124	if (!ioprio_blkg)
125		return NULL;
126
127	return &ioprio_blkg->pd;
128}
129
130static void ioprio_free_pd(struct blkg_policy_data *pd)
131{
132	struct ioprio_blkg *ioprio_blkg = pd_to_ioprio(pd);
133
134	kfree(ioprio_blkg);
135}
136
137static struct blkcg_policy_data *ioprio_alloc_cpd(gfp_t gfp)
138{
139	struct ioprio_blkcg *blkcg;
140
141	blkcg = kzalloc(sizeof(*blkcg), gfp);
142	if (!blkcg)
143		return NULL;
144	blkcg->prio_policy = POLICY_NO_CHANGE;
145	return &blkcg->cpd;
146}
147
148static void ioprio_free_cpd(struct blkcg_policy_data *cpd)
149{
150	struct ioprio_blkcg *blkcg = container_of(cpd, typeof(*blkcg), cpd);
151
152	kfree(blkcg);
153}
154
155#define IOPRIO_ATTRS						\
156	{							\
157		.name		= "prio.class",			\
158		.seq_show	= ioprio_show_prio_policy,	\
159		.write		= ioprio_set_prio_policy,	\
160	},							\
161	{ } /* sentinel */
162
163/* cgroup v2 attributes */
164static struct cftype ioprio_files[] = {
165	IOPRIO_ATTRS
166};
167
168/* cgroup v1 attributes */
169static struct cftype ioprio_legacy_files[] = {
170	IOPRIO_ATTRS
171};
172
173static struct blkcg_policy ioprio_policy = {
174	.dfl_cftypes	= ioprio_files,
175	.legacy_cftypes = ioprio_legacy_files,
176
177	.cpd_alloc_fn	= ioprio_alloc_cpd,
178	.cpd_free_fn	= ioprio_free_cpd,
179
180	.pd_alloc_fn	= ioprio_alloc_pd,
181	.pd_free_fn	= ioprio_free_pd,
182};
183
184void blkcg_set_ioprio(struct bio *bio)
185{
186	struct ioprio_blkcg *blkcg = ioprio_blkcg_from_bio(bio);
187	u16 prio;
188
189	if (!blkcg || blkcg->prio_policy == POLICY_NO_CHANGE)
190		return;
191
192	/*
193	 * Except for IOPRIO_CLASS_NONE, higher I/O priority numbers
194	 * correspond to a lower priority. Hence, the max_t() below selects
195	 * the lower priority of bi_ioprio and the cgroup I/O priority class.
196	 * If the bio I/O priority equals IOPRIO_CLASS_NONE, the cgroup I/O
197	 * priority is assigned to the bio.
198	 */
199	prio = max_t(u16, bio->bi_ioprio,
200			IOPRIO_PRIO_VALUE(blkcg->prio_policy, 0));
201	if (prio > bio->bi_ioprio)
202		bio->bi_ioprio = prio;
203}
204
205void blk_ioprio_exit(struct gendisk *disk)
206{
207	blkcg_deactivate_policy(disk->queue, &ioprio_policy);
208}
209
210int blk_ioprio_init(struct gendisk *disk)
211{
212	return blkcg_activate_policy(disk->queue, &ioprio_policy);
213}
214
215static int __init ioprio_init(void)
216{
217	return blkcg_policy_register(&ioprio_policy);
218}
219
220static void __exit ioprio_exit(void)
221{
222	blkcg_policy_unregister(&ioprio_policy);
223}
224
225module_init(ioprio_init);
226module_exit(ioprio_exit);