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 /* SPDX-License-Identifier: GPL-2.0 */
 /*
  * include/linux/backing-dev.h
  *
  * low-level device information and state which is propagated up through
  * to high-level code.
  */
 
 #ifndef _LINUX_BACKING_DEV_H
 #define _LINUX_BACKING_DEV_H
 
 #include <linux/kernel.h>
 #include <linux/fs.h>
 #include <linux/sched.h>
 #include <linux/device.h>
 #include <linux/writeback.h>
 #include <linux/backing-dev-defs.h>
 #include <linux/slab.h>
 
 static inline struct backing_dev_info *bdi_get(struct backing_dev_info *bdi)
 {
     kref_get(&bdi->refcnt);
     return bdi;
 }
 
 struct backing_dev_info *bdi_get_by_id(u64 id);
 void bdi_put(struct backing_dev_info *bdi);
 
 __printf(2, 3)
 int bdi_register(struct backing_dev_info *bdi, const char *fmt, ...);
 __printf(2, 0)
 int bdi_register_va(struct backing_dev_info *bdi, const char *fmt,
             va_list args);
 void bdi_set_owner(struct backing_dev_info *bdi, struct device *owner);
 void bdi_unregister(struct backing_dev_info *bdi);
 
 struct backing_dev_info *bdi_alloc(int node_id);
 
 void wb_start_background_writeback(struct bdi_writeback *wb);
 void wb_workfn(struct work_struct *work);
 void wb_wakeup_delayed(struct bdi_writeback *wb);
 
 void wb_wait_for_completion(struct wb_completion *done);
 
 extern spinlock_t bdi_lock;
 extern struct list_head bdi_list;
 
 extern struct workqueue_struct *bdi_wq;
 extern struct workqueue_struct *bdi_async_bio_wq;
 
 static inline bool wb_has_dirty_io(struct bdi_writeback *wb)
 {
     return test_bit(WB_has_dirty_io, &wb->state);
 }
 
 static inline bool bdi_has_dirty_io(struct backing_dev_info *bdi)
 {
     /*
      * @bdi->tot_write_bandwidth is guaranteed to be > 0 if there are
      * any dirty wbs.  See wb_update_write_bandwidth().
      */
     return atomic_long_read(&bdi->tot_write_bandwidth);
 }
 
 static inline void wb_stat_mod(struct bdi_writeback *wb,
                  enum wb_stat_item item, s64 amount)
 {
     percpu_counter_add_batch(&wb->stat[item], amount, WB_STAT_BATCH);
 }
 
 static inline void inc_wb_stat(struct bdi_writeback *wb, enum wb_stat_item item)
 {
     wb_stat_mod(wb, item, 1);
 }
 
 static inline void dec_wb_stat(struct bdi_writeback *wb, enum wb_stat_item item)
 {
     wb_stat_mod(wb, item, -1);
 }
 
 static inline s64 wb_stat(struct bdi_writeback *wb, enum wb_stat_item item)
 {
     return percpu_counter_read_positive(&wb->stat[item]);
 }
 
 static inline s64 wb_stat_sum(struct bdi_writeback *wb, enum wb_stat_item item)
 {
     return percpu_counter_sum_positive(&wb->stat[item]);
 }
 
 extern void wb_writeout_inc(struct bdi_writeback *wb);
 
 /*
  * maximal error of a stat counter.
  */
 static inline unsigned long wb_stat_error(void)
 {
 #ifdef CONFIG_SMP
     return nr_cpu_ids * WB_STAT_BATCH;
 #else
     return 1;
 #endif
 }
 
 int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio);
 int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned int max_ratio);
 
 /*
  * Flags in backing_dev_info::capability
  *
  * BDI_CAP_WRITEBACK:       Supports dirty page writeback, and dirty pages
  *              should contribute to accounting
  * BDI_CAP_WRITEBACK_ACCT:  Automatically account writeback pages
  * BDI_CAP_STRICTLIMIT:     Keep number of dirty pages below bdi threshold
  */
 #define BDI_CAP_WRITEBACK       (1 << 0)
 #define BDI_CAP_WRITEBACK_ACCT      (1 << 1)
 #define BDI_CAP_STRICTLIMIT     (1 << 2)
 
 extern struct backing_dev_info noop_backing_dev_info;
 
 int bdi_init(struct backing_dev_info *bdi);
 
 /**
  * writeback_in_progress - determine whether there is writeback in progress
  * @wb: bdi_writeback of interest
  *
  * Determine whether there is writeback waiting to be handled against a
  * bdi_writeback.
  */
 static inline bool writeback_in_progress(struct bdi_writeback *wb)
 {
     return test_bit(WB_writeback_running, &wb->state);
 }
 
 struct backing_dev_info *inode_to_bdi(struct inode *inode);
 
 static inline bool mapping_can_writeback(struct address_space *mapping)
 {
     return inode_to_bdi(mapping->host)->capabilities & BDI_CAP_WRITEBACK;
 }
 
 #ifdef CONFIG_CGROUP_WRITEBACK
 
 struct bdi_writeback *wb_get_lookup(struct backing_dev_info *bdi,
                     struct cgroup_subsys_state *memcg_css);
 struct bdi_writeback *wb_get_create(struct backing_dev_info *bdi,
                     struct cgroup_subsys_state *memcg_css,
                     gfp_t gfp);
 void wb_memcg_offline(struct mem_cgroup *memcg);
 void wb_blkcg_offline(struct cgroup_subsys_state *css);
 
 /**
  * inode_cgwb_enabled - test whether cgroup writeback is enabled on an inode
  * @inode: inode of interest
  *
  * Cgroup writeback requires support from the filesystem.  Also, both memcg and
  * iocg have to be on the default hierarchy.  Test whether all conditions are
  * met.
  *
  * Note that the test result may change dynamically on the same inode
  * depending on how memcg and iocg are configured.
  */
 static inline bool inode_cgwb_enabled(struct inode *inode)
 {
     struct backing_dev_info *bdi = inode_to_bdi(inode);
 
     return cgroup_subsys_on_dfl(memory_cgrp_subsys) &&
         cgroup_subsys_on_dfl(io_cgrp_subsys) &&
         (bdi->capabilities & BDI_CAP_WRITEBACK) &&
         (inode->i_sb->s_iflags & SB_I_CGROUPWB);
 }
 
 /**
  * wb_find_current - find wb for %current on a bdi
  * @bdi: bdi of interest
  *
  * Find the wb of @bdi which matches both the memcg and blkcg of %current.
  * Must be called under rcu_read_lock() which protects the returend wb.
  * NULL if not found.
  */
 static inline struct bdi_writeback *wb_find_current(struct backing_dev_info *bdi)
 {
     struct cgroup_subsys_state *memcg_css;
     struct bdi_writeback *wb;
 
     memcg_css = task_css(current, memory_cgrp_id);
     if (!memcg_css->parent)
         return &bdi->wb;
 
     wb = radix_tree_lookup(&bdi->cgwb_tree, memcg_css->id);
 
     /*
      * %current's blkcg equals the effective blkcg of its memcg.  No
      * need to use the relatively expensive cgroup_get_e_css().
      */
     if (likely(wb && wb->blkcg_css == task_css(current, io_cgrp_id)))
         return wb;
     return NULL;
 }
 
 /**
  * wb_get_create_current - get or create wb for %current on a bdi
  * @bdi: bdi of interest
  * @gfp: allocation mask
  *
  * Equivalent to wb_get_create() on %current's memcg.  This function is
  * called from a relatively hot path and optimizes the common cases using
  * wb_find_current().
  */
 static inline struct bdi_writeback *
 wb_get_create_current(struct backing_dev_info *bdi, gfp_t gfp)
 {
     struct bdi_writeback *wb;
 
     rcu_read_lock();
     wb = wb_find_current(bdi);
     if (wb && unlikely(!wb_tryget(wb)))
         wb = NULL;
     rcu_read_unlock();
 
     if (unlikely(!wb)) {
         struct cgroup_subsys_state *memcg_css;
 
         memcg_css = task_get_css(current, memory_cgrp_id);
         wb = wb_get_create(bdi, memcg_css, gfp);
         css_put(memcg_css);
     }
     return wb;
 }
 
 /**
  * inode_to_wb - determine the wb of an inode
  * @inode: inode of interest
  *
  * Returns the wb @inode is currently associated with.  The caller must be
  * holding either @inode->i_lock, the i_pages lock, or the
  * associated wb's list_lock.
  */
 static inline struct bdi_writeback *inode_to_wb(const struct inode *inode)
 {
 #ifdef CONFIG_LOCKDEP
     WARN_ON_ONCE(debug_locks &&
              (!lockdep_is_held(&inode->i_lock) &&
               !lockdep_is_held(&inode->i_mapping->i_pages.xa_lock) &&
               !lockdep_is_held(&inode->i_wb->list_lock)));
 #endif
     return inode->i_wb;
 }
 
 static inline struct bdi_writeback *inode_to_wb_wbc(
                 struct inode *inode,
                 struct writeback_control *wbc)
 {
     /*
      * If wbc does not have inode attached, it means cgroup writeback was
      * disabled when wbc started. Just use the default wb in that case.
      */
     return wbc->wb ? wbc->wb : &inode_to_bdi(inode)->wb;
 }
 
 /**
  * unlocked_inode_to_wb_begin - begin unlocked inode wb access transaction
  * @inode: target inode
  * @cookie: output param, to be passed to the end function
  *
  * The caller wants to access the wb associated with @inode but isn't
  * holding inode->i_lock, the i_pages lock or wb->list_lock.  This
  * function determines the wb associated with @inode and ensures that the
  * association doesn't change until the transaction is finished with
  * unlocked_inode_to_wb_end().
  *
  * The caller must call unlocked_inode_to_wb_end() with *@cookie afterwards and
  * can't sleep during the transaction.  IRQs may or may not be disabled on
  * return.
  */
 static inline struct bdi_writeback *
 unlocked_inode_to_wb_begin(struct inode *inode, struct wb_lock_cookie *cookie)
 {
     rcu_read_lock();
 
     /*
      * Paired with store_release in inode_switch_wbs_work_fn() and
      * ensures that we see the new wb if we see cleared I_WB_SWITCH.
      */
     cookie->locked = smp_load_acquire(&inode->i_state) & I_WB_SWITCH;
 
     if (unlikely(cookie->locked))
         xa_lock_irqsave(&inode->i_mapping->i_pages, cookie->flags);
 
     /*
      * Protected by either !I_WB_SWITCH + rcu_read_lock() or the i_pages
      * lock.  inode_to_wb() will bark.  Deref directly.
      */
     return inode->i_wb;
 }
 
 /**
  * unlocked_inode_to_wb_end - end inode wb access transaction
  * @inode: target inode
  * @cookie: @cookie from unlocked_inode_to_wb_begin()
  */
 static inline void unlocked_inode_to_wb_end(struct inode *inode,
                         struct wb_lock_cookie *cookie)
 {
     if (unlikely(cookie->locked))
         xa_unlock_irqrestore(&inode->i_mapping->i_pages, cookie->flags);
 
     rcu_read_unlock();
 }
 
 #else   /* CONFIG_CGROUP_WRITEBACK */
 
 static inline bool inode_cgwb_enabled(struct inode *inode)
 {
     return false;
 }
 
 static inline struct bdi_writeback *wb_find_current(struct backing_dev_info *bdi)
 {
     return &bdi->wb;
 }
 
 static inline struct bdi_writeback *
 wb_get_create_current(struct backing_dev_info *bdi, gfp_t gfp)
 {
     return &bdi->wb;
 }
 
 static inline struct bdi_writeback *inode_to_wb(struct inode *inode)
 {
     return &inode_to_bdi(inode)->wb;
 }
 
 static inline struct bdi_writeback *inode_to_wb_wbc(
                 struct inode *inode,
                 struct writeback_control *wbc)
 {
     return inode_to_wb(inode);
 }
 
 
 static inline struct bdi_writeback *
 unlocked_inode_to_wb_begin(struct inode *inode, struct wb_lock_cookie *cookie)
 {
     return inode_to_wb(inode);
 }
 
 static inline void unlocked_inode_to_wb_end(struct inode *inode,
                         struct wb_lock_cookie *cookie)
 {
 }
 
 static inline void wb_memcg_offline(struct mem_cgroup *memcg)
 {
 }
 
 static inline void wb_blkcg_offline(struct cgroup_subsys_state *css)
 {
 }
 
 #endif  /* CONFIG_CGROUP_WRITEBACK */
 
 const char *bdi_dev_name(struct backing_dev_info *bdi);
 
 #endif  /* _LINUX_BACKING_DEV_H */

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