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/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _BLK_CGROUP_H
#define _BLK_CGROUP_H
/*
* Common Block IO controller cgroup interface
*
* Based on ideas and code from CFQ, CFS and BFQ:
* Copyright (C) 2003 Jens Axboe <[email protected]>
*
* Copyright (C) 2008 Fabio Checconi <[email protected]>
* Paolo Valente <[email protected]>
*
* Copyright (C) 2009 Vivek Goyal <[email protected]>
* Nauman Rafique <[email protected]>
*/
#include <linux/cgroup.h>
#include <linux/percpu.h>
#include <linux/percpu_counter.h>
#include <linux/u64_stats_sync.h>
#include <linux/seq_file.h>
#include <linux/radix-tree.h>
#include <linux/blkdev.h>
#include <linux/atomic.h>
#include <linux/kthread.h>
#include <linux/fs.h>
#include <linux/blk-mq.h>
/* percpu_counter batch for blkg_[rw]stats, per-cpu drift doesn't matter */
#define BLKG_STAT_CPU_BATCH (INT_MAX / 2)
/* Max limits for throttle policy */
#define THROTL_IOPS_MAX UINT_MAX
#define FC_APPID_LEN 129
#ifdef CONFIG_BLK_CGROUP
enum blkg_iostat_type {
BLKG_IOSTAT_READ,
BLKG_IOSTAT_WRITE,
BLKG_IOSTAT_DISCARD,
BLKG_IOSTAT_NR,
};
struct blkcg_gq;
struct blkcg {
struct cgroup_subsys_state css;
spinlock_t lock;
refcount_t online_pin;
struct radix_tree_root blkg_tree;
struct blkcg_gq __rcu *blkg_hint;
struct hlist_head blkg_list;
struct blkcg_policy_data *cpd[BLKCG_MAX_POLS];
struct list_head all_blkcgs_node;
#ifdef CONFIG_BLK_CGROUP_FC_APPID
char fc_app_id[FC_APPID_LEN];
#endif
#ifdef CONFIG_CGROUP_WRITEBACK
struct list_head cgwb_list;
#endif
};
struct blkg_iostat {
u64 bytes[BLKG_IOSTAT_NR];
u64 ios[BLKG_IOSTAT_NR];
};
struct blkg_iostat_set {
struct u64_stats_sync sync;
struct blkg_iostat cur;
struct blkg_iostat last;
};
/*
* A blkcg_gq (blkg) is association between a block cgroup (blkcg) and a
* request_queue (q). This is used by blkcg policies which need to track
* information per blkcg - q pair.
*
* There can be multiple active blkcg policies and each blkg:policy pair is
* represented by a blkg_policy_data which is allocated and freed by each
* policy's pd_alloc/free_fn() methods. A policy can allocate private data
* area by allocating larger data structure which embeds blkg_policy_data
* at the beginning.
*/
struct blkg_policy_data {
/* the blkg and policy id this per-policy data belongs to */
struct blkcg_gq *blkg;
int plid;
};
/*
* Policies that need to keep per-blkcg data which is independent from any
* request_queue associated to it should implement cpd_alloc/free_fn()
* methods. A policy can allocate private data area by allocating larger
* data structure which embeds blkcg_policy_data at the beginning.
* cpd_init() is invoked to let each policy handle per-blkcg data.
*/
struct blkcg_policy_data {
/* the blkcg and policy id this per-policy data belongs to */
struct blkcg *blkcg;
int plid;
};
/* association between a blk cgroup and a request queue */
struct blkcg_gq {
/* Pointer to the associated request_queue */
struct request_queue *q;
struct list_head q_node;
struct hlist_node blkcg_node;
struct blkcg *blkcg;
/* all non-root blkcg_gq's are guaranteed to have access to parent */
struct blkcg_gq *parent;
/* reference count */
struct percpu_ref refcnt;
/* is this blkg online? protected by both blkcg and q locks */
bool online;
struct blkg_iostat_set __percpu *iostat_cpu;
struct blkg_iostat_set iostat;
struct blkg_policy_data *pd[BLKCG_MAX_POLS];
spinlock_t async_bio_lock;
struct bio_list async_bios;
struct work_struct async_bio_work;
atomic_t use_delay;
atomic64_t delay_nsec;
atomic64_t delay_start;
u64 last_delay;
int last_use;
struct rcu_head rcu_head;
};
typedef struct blkcg_policy_data *(blkcg_pol_alloc_cpd_fn)(gfp_t gfp);
typedef void (blkcg_pol_init_cpd_fn)(struct blkcg_policy_data *cpd);
typedef void (blkcg_pol_free_cpd_fn)(struct blkcg_policy_data *cpd);
typedef void (blkcg_pol_bind_cpd_fn)(struct blkcg_policy_data *cpd);
typedef struct blkg_policy_data *(blkcg_pol_alloc_pd_fn)(gfp_t gfp,
struct request_queue *q, struct blkcg *blkcg);
typedef void (blkcg_pol_init_pd_fn)(struct blkg_policy_data *pd);
typedef void (blkcg_pol_online_pd_fn)(struct blkg_policy_data *pd);
typedef void (blkcg_pol_offline_pd_fn)(struct blkg_policy_data *pd);
typedef void (blkcg_pol_free_pd_fn)(struct blkg_policy_data *pd);
typedef void (blkcg_pol_reset_pd_stats_fn)(struct blkg_policy_data *pd);
typedef bool (blkcg_pol_stat_pd_fn)(struct blkg_policy_data *pd,
struct seq_file *s);
struct blkcg_policy {
int plid;
/* cgroup files for the policy */
struct cftype *dfl_cftypes;
struct cftype *legacy_cftypes;
/* operations */
blkcg_pol_alloc_cpd_fn *cpd_alloc_fn;
blkcg_pol_init_cpd_fn *cpd_init_fn;
blkcg_pol_free_cpd_fn *cpd_free_fn;
blkcg_pol_bind_cpd_fn *cpd_bind_fn;
blkcg_pol_alloc_pd_fn *pd_alloc_fn;
blkcg_pol_init_pd_fn *pd_init_fn;
blkcg_pol_online_pd_fn *pd_online_fn;
blkcg_pol_offline_pd_fn *pd_offline_fn;
blkcg_pol_free_pd_fn *pd_free_fn;
blkcg_pol_reset_pd_stats_fn *pd_reset_stats_fn;
blkcg_pol_stat_pd_fn *pd_stat_fn;
};
extern struct blkcg blkcg_root;
extern struct cgroup_subsys_state * const blkcg_root_css;
extern bool blkcg_debug_stats;
struct blkcg_gq *blkg_lookup_slowpath(struct blkcg *blkcg,
struct request_queue *q, bool update_hint);
int blkcg_init_queue(struct request_queue *q);
void blkcg_exit_queue(struct request_queue *q);
/* Blkio controller policy registration */
int blkcg_policy_register(struct blkcg_policy *pol);
void blkcg_policy_unregister(struct blkcg_policy *pol);
int blkcg_activate_policy(struct request_queue *q,
const struct blkcg_policy *pol);
void blkcg_deactivate_policy(struct request_queue *q,
const struct blkcg_policy *pol);
const char *blkg_dev_name(struct blkcg_gq *blkg);
void blkcg_print_blkgs(struct seq_file *sf, struct blkcg *blkcg,
u64 (*prfill)(struct seq_file *,
struct blkg_policy_data *, int),
const struct blkcg_policy *pol, int data,
bool show_total);
u64 __blkg_prfill_u64(struct seq_file *sf, struct blkg_policy_data *pd, u64 v);
struct blkg_conf_ctx {
struct block_device *bdev;
struct blkcg_gq *blkg;
char *body;
};
struct block_device *blkcg_conf_open_bdev(char **inputp);
int blkg_conf_prep(struct blkcg *blkcg, const struct blkcg_policy *pol,
char *input, struct blkg_conf_ctx *ctx);
void blkg_conf_finish(struct blkg_conf_ctx *ctx);
/**
* blkcg_css - find the current css
*
* Find the css associated with either the kthread or the current task.
* This may return a dying css, so it is up to the caller to use tryget logic
* to confirm it is alive and well.
*/
static inline struct cgroup_subsys_state *blkcg_css(void)
{
struct cgroup_subsys_state *css;
css = kthread_blkcg();
if (css)
return css;
return task_css(current, io_cgrp_id);
}
static inline struct blkcg *css_to_blkcg(struct cgroup_subsys_state *css)
{
return css ? container_of(css, struct blkcg, css) : NULL;
}
/**
* __bio_blkcg - internal, inconsistent version to get blkcg
*
* DO NOT USE.
* This function is inconsistent and consequently is dangerous to use. The
* first part of the function returns a blkcg where a reference is owned by the
* bio. This means it does not need to be rcu protected as it cannot go away
* with the bio owning a reference to it. However, the latter potentially gets
* it from task_css(). This can race against task migration and the cgroup
* dying. It is also semantically different as it must be called rcu protected
* and is susceptible to failure when trying to get a reference to it.
* Therefore, it is not ok to assume that *_get() will always succeed on the
* blkcg returned here.
*/
static inline struct blkcg *__bio_blkcg(struct bio *bio)
{
if (bio && bio->bi_blkg)
return bio->bi_blkg->blkcg;
return css_to_blkcg(blkcg_css());
}
/**
* bio_blkcg - grab the blkcg associated with a bio
* @bio: target bio
*
* This returns the blkcg associated with a bio, %NULL if not associated.
* Callers are expected to either handle %NULL or know association has been
* done prior to calling this.
*/
static inline struct blkcg *bio_blkcg(struct bio *bio)
{
if (bio && bio->bi_blkg)
return bio->bi_blkg->blkcg;
return NULL;
}
static inline bool blk_cgroup_congested(void)
{
struct cgroup_subsys_state *css;
bool ret = false;
rcu_read_lock();
css = kthread_blkcg();
if (!css)
css = task_css(current, io_cgrp_id);
while (css) {
if (atomic_read(&css->cgroup->congestion_count)) {
ret = true;
break;
}
css = css->parent;
}
rcu_read_unlock();
return ret;
}
/**
* bio_issue_as_root_blkg - see if this bio needs to be issued as root blkg
* @return: true if this bio needs to be submitted with the root blkg context.
*
* In order to avoid priority inversions we sometimes need to issue a bio as if
* it were attached to the root blkg, and then backcharge to the actual owning
* blkg. The idea is we do bio_blkcg() to look up the actual context for the
* bio and attach the appropriate blkg to the bio. Then we call this helper and
* if it is true run with the root blkg for that queue and then do any
* backcharging to the originating cgroup once the io is complete.
*/
static inline bool bio_issue_as_root_blkg(struct bio *bio)
{
return (bio->bi_opf & (REQ_META | REQ_SWAP)) != 0;
}
/**
* blkcg_parent - get the parent of a blkcg
* @blkcg: blkcg of interest
*
* Return the parent blkcg of @blkcg. Can be called anytime.
*/
static inline struct blkcg *blkcg_parent(struct blkcg *blkcg)
{
return css_to_blkcg(blkcg->css.parent);
}
/**
* __blkg_lookup - internal version of blkg_lookup()
* @blkcg: blkcg of interest
* @q: request_queue of interest
* @update_hint: whether to update lookup hint with the result or not
*
* This is internal version and shouldn't be used by policy
* implementations. Looks up blkgs for the @blkcg - @q pair regardless of
* @q's bypass state. If @update_hint is %true, the caller should be
* holding @q->queue_lock and lookup hint is updated on success.
*/
static inline struct blkcg_gq *__blkg_lookup(struct blkcg *blkcg,
struct request_queue *q,
bool update_hint)
{
struct blkcg_gq *blkg;
if (blkcg == &blkcg_root)
return q->root_blkg;
blkg = rcu_dereference(blkcg->blkg_hint);
if (blkg && blkg->q == q)
return blkg;
return blkg_lookup_slowpath(blkcg, q, update_hint);
}
/**
* blkg_lookup - lookup blkg for the specified blkcg - q pair
* @blkcg: blkcg of interest
* @q: request_queue of interest
*
* Lookup blkg for the @blkcg - @q pair. This function should be called
* under RCU read lock.
*/
static inline struct blkcg_gq *blkg_lookup(struct blkcg *blkcg,
struct request_queue *q)
{
WARN_ON_ONCE(!rcu_read_lock_held());
return __blkg_lookup(blkcg, q, false);
}
/**
* blk_queue_root_blkg - return blkg for the (blkcg_root, @q) pair
* @q: request_queue of interest
*
* Lookup blkg for @q at the root level. See also blkg_lookup().
*/
static inline struct blkcg_gq *blk_queue_root_blkg(struct request_queue *q)
{
return q->root_blkg;
}
/**
* blkg_to_pdata - get policy private data
* @blkg: blkg of interest
* @pol: policy of interest
*
* Return pointer to private data associated with the @blkg-@pol pair.
*/
static inline struct blkg_policy_data *blkg_to_pd(struct blkcg_gq *blkg,
struct blkcg_policy *pol)
{
return blkg ? blkg->pd[pol->plid] : NULL;
}
static inline struct blkcg_policy_data *blkcg_to_cpd(struct blkcg *blkcg,
struct blkcg_policy *pol)
{
return blkcg ? blkcg->cpd[pol->plid] : NULL;
}
/**
* pdata_to_blkg - get blkg associated with policy private data
* @pd: policy private data of interest
*
* @pd is policy private data. Determine the blkg it's associated with.
*/
static inline struct blkcg_gq *pd_to_blkg(struct blkg_policy_data *pd)
{
return pd ? pd->blkg : NULL;
}
static inline struct blkcg *cpd_to_blkcg(struct blkcg_policy_data *cpd)
{
return cpd ? cpd->blkcg : NULL;
}
extern void blkcg_destroy_blkgs(struct blkcg *blkcg);
/**
* blkcg_pin_online - pin online state
* @blkcg: blkcg of interest
*
* While pinned, a blkcg is kept online. This is primarily used to
* impedance-match blkg and cgwb lifetimes so that blkg doesn't go offline
* while an associated cgwb is still active.
*/
static inline void blkcg_pin_online(struct blkcg *blkcg)
{
refcount_inc(&blkcg->online_pin);
}
/**
* blkcg_unpin_online - unpin online state
* @blkcg: blkcg of interest
*
* This is primarily used to impedance-match blkg and cgwb lifetimes so
* that blkg doesn't go offline while an associated cgwb is still active.
* When this count goes to zero, all active cgwbs have finished so the
* blkcg can continue destruction by calling blkcg_destroy_blkgs().
*/
static inline void blkcg_unpin_online(struct blkcg *blkcg)
{
do {
if (!refcount_dec_and_test(&blkcg->online_pin))
break;
blkcg_destroy_blkgs(blkcg);
blkcg = blkcg_parent(blkcg);
} while (blkcg);
}
/**
* blkg_path - format cgroup path of blkg
* @blkg: blkg of interest
* @buf: target buffer
* @buflen: target buffer length
*
* Format the path of the cgroup of @blkg into @buf.
*/
static inline int blkg_path(struct blkcg_gq *blkg, char *buf, int buflen)
{
return cgroup_path(blkg->blkcg->css.cgroup, buf, buflen);
}
/**
* blkg_get - get a blkg reference
* @blkg: blkg to get
*
* The caller should be holding an existing reference.
*/
static inline void blkg_get(struct blkcg_gq *blkg)
{
percpu_ref_get(&blkg->refcnt);
}
/**
* blkg_tryget - try and get a blkg reference
* @blkg: blkg to get
*
* This is for use when doing an RCU lookup of the blkg. We may be in the midst
* of freeing this blkg, so we can only use it if the refcnt is not zero.
*/
static inline bool blkg_tryget(struct blkcg_gq *blkg)
{
return blkg && percpu_ref_tryget(&blkg->refcnt);
}
/**
* blkg_put - put a blkg reference
* @blkg: blkg to put
*/
static inline void blkg_put(struct blkcg_gq *blkg)
{
percpu_ref_put(&blkg->refcnt);
}
/**
* blkg_for_each_descendant_pre - pre-order walk of a blkg's descendants
* @d_blkg: loop cursor pointing to the current descendant
* @pos_css: used for iteration
* @p_blkg: target blkg to walk descendants of
*
* Walk @c_blkg through the descendants of @p_blkg. Must be used with RCU
* read locked. If called under either blkcg or queue lock, the iteration
* is guaranteed to include all and only online blkgs. The caller may
* update @pos_css by calling css_rightmost_descendant() to skip subtree.
* @p_blkg is included in the iteration and the first node to be visited.
*/
#define blkg_for_each_descendant_pre(d_blkg, pos_css, p_blkg) \
css_for_each_descendant_pre((pos_css), &(p_blkg)->blkcg->css) \
if (((d_blkg) = __blkg_lookup(css_to_blkcg(pos_css), \
(p_blkg)->q, false)))
/**
* blkg_for_each_descendant_post - post-order walk of a blkg's descendants
* @d_blkg: loop cursor pointing to the current descendant
* @pos_css: used for iteration
* @p_blkg: target blkg to walk descendants of
*
* Similar to blkg_for_each_descendant_pre() but performs post-order
* traversal instead. Synchronization rules are the same. @p_blkg is
* included in the iteration and the last node to be visited.
*/
#define blkg_for_each_descendant_post(d_blkg, pos_css, p_blkg) \
css_for_each_descendant_post((pos_css), &(p_blkg)->blkcg->css) \
if (((d_blkg) = __blkg_lookup(css_to_blkcg(pos_css), \
(p_blkg)->q, false)))
bool __blkcg_punt_bio_submit(struct bio *bio);
static inline bool blkcg_punt_bio_submit(struct bio *bio)
{
if (bio->bi_opf & REQ_CGROUP_PUNT)
return __blkcg_punt_bio_submit(bio);
else
return false;
}
static inline void blkcg_bio_issue_init(struct bio *bio)
{
bio_issue_init(&bio->bi_issue, bio_sectors(bio));
}
static inline void blkcg_use_delay(struct blkcg_gq *blkg)
{
if (WARN_ON_ONCE(atomic_read(&blkg->use_delay) < 0))
return;
if (atomic_add_return(1, &blkg->use_delay) == 1)
atomic_inc(&blkg->blkcg->css.cgroup->congestion_count);
}
static inline int blkcg_unuse_delay(struct blkcg_gq *blkg)
{
int old = atomic_read(&blkg->use_delay);
if (WARN_ON_ONCE(old < 0))
return 0;
if (old == 0)
return 0;
/*
* We do this song and dance because we can race with somebody else
* adding or removing delay. If we just did an atomic_dec we'd end up
* negative and we'd already be in trouble. We need to subtract 1 and
* then check to see if we were the last delay so we can drop the
* congestion count on the cgroup.
*/
while (old) {
int cur = atomic_cmpxchg(&blkg->use_delay, old, old - 1);
if (cur == old)
break;
old = cur;
}
if (old == 0)
return 0;
if (old == 1)
atomic_dec(&blkg->blkcg->css.cgroup->congestion_count);
return 1;
}
/**
* blkcg_set_delay - Enable allocator delay mechanism with the specified delay amount
* @blkg: target blkg
* @delay: delay duration in nsecs
*
* When enabled with this function, the delay is not decayed and must be
* explicitly cleared with blkcg_clear_delay(). Must not be mixed with
* blkcg_[un]use_delay() and blkcg_add_delay() usages.
*/
static inline void blkcg_set_delay(struct blkcg_gq *blkg, u64 delay)
{
int old = atomic_read(&blkg->use_delay);
/* We only want 1 person setting the congestion count for this blkg. */
if (!old && atomic_cmpxchg(&blkg->use_delay, old, -1) == old)
atomic_inc(&blkg->blkcg->css.cgroup->congestion_count);
atomic64_set(&blkg->delay_nsec, delay);
}
/**
* blkcg_clear_delay - Disable allocator delay mechanism
* @blkg: target blkg
*
* Disable use_delay mechanism. See blkcg_set_delay().
*/
static inline void blkcg_clear_delay(struct blkcg_gq *blkg)
{
int old = atomic_read(&blkg->use_delay);
/* We only want 1 person clearing the congestion count for this blkg. */
if (old && atomic_cmpxchg(&blkg->use_delay, old, 0) == old)
atomic_dec(&blkg->blkcg->css.cgroup->congestion_count);
}
/**
* blk_cgroup_mergeable - Determine whether to allow or disallow merges
* @rq: request to merge into
* @bio: bio to merge
*
* @bio and @rq should belong to the same cgroup and their issue_as_root should
* match. The latter is necessary as we don't want to throttle e.g. a metadata
* update because it happens to be next to a regular IO.
*/
static inline bool blk_cgroup_mergeable(struct request *rq, struct bio *bio)
{
return rq->bio->bi_blkg == bio->bi_blkg &&
bio_issue_as_root_blkg(rq->bio) == bio_issue_as_root_blkg(bio);
}
void blk_cgroup_bio_start(struct bio *bio);
void blkcg_add_delay(struct blkcg_gq *blkg, u64 now, u64 delta);
void blkcg_schedule_throttle(struct request_queue *q, bool use_memdelay);
void blkcg_maybe_throttle_current(void);
#else /* CONFIG_BLK_CGROUP */
struct blkcg {
};
struct blkg_policy_data {
};
struct blkcg_policy_data {
};
struct blkcg_gq {
};
struct blkcg_policy {
};
#define blkcg_root_css ((struct cgroup_subsys_state *)ERR_PTR(-EINVAL))
static inline void blkcg_maybe_throttle_current(void) { }
static inline bool blk_cgroup_congested(void) { return false; }
#ifdef CONFIG_BLOCK
static inline void blkcg_schedule_throttle(struct request_queue *q, bool use_memdelay) { }
static inline struct blkcg_gq *blkg_lookup(struct blkcg *blkcg, void *key) { return NULL; }
static inline struct blkcg_gq *blk_queue_root_blkg(struct request_queue *q)
{ return NULL; }
static inline int blkcg_init_queue(struct request_queue *q) { return 0; }
static inline void blkcg_exit_queue(struct request_queue *q) { }
static inline int blkcg_policy_register(struct blkcg_policy *pol) { return 0; }
static inline void blkcg_policy_unregister(struct blkcg_policy *pol) { }
static inline int blkcg_activate_policy(struct request_queue *q,
const struct blkcg_policy *pol) { return 0; }
static inline void blkcg_deactivate_policy(struct request_queue *q,
const struct blkcg_policy *pol) { }
static inline struct blkcg *__bio_blkcg(struct bio *bio) { return NULL; }
static inline struct blkcg *bio_blkcg(struct bio *bio) { return NULL; }
static inline struct blkg_policy_data *blkg_to_pd(struct blkcg_gq *blkg,
struct blkcg_policy *pol) { return NULL; }
static inline struct blkcg_gq *pd_to_blkg(struct blkg_policy_data *pd) { return NULL; }
static inline char *blkg_path(struct blkcg_gq *blkg) { return NULL; }
static inline void blkg_get(struct blkcg_gq *blkg) { }
static inline void blkg_put(struct blkcg_gq *blkg) { }
static inline bool blkcg_punt_bio_submit(struct bio *bio) { return false; }
static inline void blkcg_bio_issue_init(struct bio *bio) { }
static inline void blk_cgroup_bio_start(struct bio *bio) { }
static inline bool blk_cgroup_mergeable(struct request *rq, struct bio *bio) { return true; }
#define blk_queue_for_each_rl(rl, q) \
for ((rl) = &(q)->root_rl; (rl); (rl) = NULL)
#endif /* CONFIG_BLOCK */
#endif /* CONFIG_BLK_CGROUP */
#ifdef CONFIG_BLK_CGROUP_FC_APPID
/*
* Sets the fc_app_id field associted to blkcg
* @app_id: application identifier
* @cgrp_id: cgroup id
* @app_id_len: size of application identifier
*/
static inline int blkcg_set_fc_appid(char *app_id, u64 cgrp_id, size_t app_id_len)
{
struct cgroup *cgrp;
struct cgroup_subsys_state *css;
struct blkcg *blkcg;
int ret = 0;
if (app_id_len > FC_APPID_LEN)
return -EINVAL;
cgrp = cgroup_get_from_id(cgrp_id);
if (!cgrp)
return -ENOENT;
css = cgroup_get_e_css(cgrp, &io_cgrp_subsys);
if (!css) {
ret = -ENOENT;
goto out_cgrp_put;
}
blkcg = css_to_blkcg(css);
/*
* There is a slight race condition on setting the appid.
* Worst case an I/O may not find the right id.
* This is no different from the I/O we let pass while obtaining
* the vmid from the fabric.
* Adding the overhead of a lock is not necessary.
*/
strlcpy(blkcg->fc_app_id, app_id, app_id_len);
css_put(css);
out_cgrp_put:
cgroup_put(cgrp);
return ret;
}
/**
* blkcg_get_fc_appid - get the fc app identifier associated with a bio
* @bio: target bio
*
* On success return the fc_app_id, on failure return NULL
*/
static inline char *blkcg_get_fc_appid(struct bio *bio)
{
if (bio && bio->bi_blkg &&
(bio->bi_blkg->blkcg->fc_app_id[0] != '\0'))
return bio->bi_blkg->blkcg->fc_app_id;
return NULL;
}
#else
static inline int blkcg_set_fc_appid(char *buf, u64 id, size_t len) { return -EINVAL; }
static inline char *blkcg_get_fc_appid(struct bio *bio) { return NULL; }
#endif /*CONFIG_BLK_CGROUP_FC_APPID*/
#endif /* _BLK_CGROUP_H */
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