text: /* 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/blkdev.h>
  #include <linux/writeback.h>
  #include <linux/blk-cgroup.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;
  }
  
  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);
  int bdi_register_owner(struct backing_dev_info *bdi, struct device *owner);
  void bdi_unregister(struct backing_dev_info *bdi);
  
  struct backing_dev_info *bdi_alloc_node(gfp_t gfp_mask, int node_id);
  static inline struct backing_dev_info *bdi_alloc(gfp_t gfp_mask)
  {
  	return bdi_alloc_node(gfp_mask, NUMA_NO_NODE);
  }
  
  void wb_start_background_writeback(struct bdi_writeback *wb);
  void wb_workfn(struct work_struct *work);
  void wb_wakeup_delayed(struct bdi_writeback *wb);
  
  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 __add_wb_stat(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)
  {
  	__add_wb_stat(wb, item, 1);
  }
  
  static inline void dec_wb_stat(struct bdi_writeback *wb, enum wb_stat_item item)
  {
  	__add_wb_stat(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
   *
   * The first three flags control whether dirty pages will contribute to the
   * VM's accounting and whether writepages() should be called for dirty pages
   * (something that would not, for example, be appropriate for ramfs)
   *
   * WARNING: these flags are closely related and should not normally be
   * used separately.  The BDI_CAP_NO_ACCT_AND_WRITEBACK combines these
   * three flags into a single convenience macro.
   *
   * BDI_CAP_NO_ACCT_DIRTY:  Dirty pages shouldn't contribute to accounting
   * BDI_CAP_NO_WRITEBACK:   Don't write pages back
   * BDI_CAP_NO_ACCT_WB:     Don't automatically account writeback pages
   * BDI_CAP_STRICTLIMIT:    Keep number of dirty pages below bdi threshold.
   *
   * BDI_CAP_CGROUP_WRITEBACK: Supports cgroup-aware writeback.
   * BDI_CAP_SYNCHRONOUS_IO: Device is so fast that asynchronous IO would be
   *			   inefficient.
   */
  #define BDI_CAP_NO_ACCT_DIRTY	0x00000001
  #define BDI_CAP_NO_WRITEBACK	0x00000002
  #define BDI_CAP_NO_ACCT_WB	0x00000004
  #define BDI_CAP_STABLE_WRITES	0x00000008
  #define BDI_CAP_STRICTLIMIT	0x00000010
  #define BDI_CAP_CGROUP_WRITEBACK 0x00000020
  #define BDI_CAP_SYNCHRONOUS_IO	0x00000040
  
  #define BDI_CAP_NO_ACCT_AND_WRITEBACK \
  	(BDI_CAP_NO_WRITEBACK | BDI_CAP_NO_ACCT_DIRTY | BDI_CAP_NO_ACCT_WB)
  
  extern struct backing_dev_info noop_backing_dev_info;
  
  /**
   * 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);
  }
  
  static inline struct backing_dev_info *inode_to_bdi(struct inode *inode)
  {
  	struct super_block *sb;
  
  	if (!inode)
  		return &noop_backing_dev_info;
  
  	sb = inode->i_sb;
  #ifdef CONFIG_BLOCK
  	if (sb_is_blkdev_sb(sb))
  		return I_BDEV(inode)->bd_bdi;
  #endif
  	return sb->s_bdi;
  }
  
  static inline int wb_congested(struct bdi_writeback *wb, int cong_bits)
  {
  	struct backing_dev_info *bdi = wb->bdi;
  
  	if (bdi->congested_fn)
  		return bdi->congested_fn(bdi->congested_data, cong_bits);
  	return wb->congested->state & cong_bits;
  }
  
  long congestion_wait(int sync, long timeout);
  long wait_iff_congested(int sync, long timeout);
  
  static inline bool bdi_cap_synchronous_io(struct backing_dev_info *bdi)
  {
  	return bdi->capabilities & BDI_CAP_SYNCHRONOUS_IO;
  }
  
  static inline bool bdi_cap_stable_pages_required(struct backing_dev_info *bdi)
  {
  	return bdi->capabilities & BDI_CAP_STABLE_WRITES;
  }
  
  static inline bool bdi_cap_writeback_dirty(struct backing_dev_info *bdi)
  {
  	return !(bdi->capabilities & BDI_CAP_NO_WRITEBACK);
  }
  
  static inline bool bdi_cap_account_dirty(struct backing_dev_info *bdi)
  {
  	return !(bdi->capabilities & BDI_CAP_NO_ACCT_DIRTY);
  }
  
  static inline bool bdi_cap_account_writeback(struct backing_dev_info *bdi)
  {
  	/* Paranoia: BDI_CAP_NO_WRITEBACK implies BDI_CAP_NO_ACCT_WB */
  	return !(bdi->capabilities & (BDI_CAP_NO_ACCT_WB |
  				      BDI_CAP_NO_WRITEBACK));
  }
  
  static inline bool mapping_cap_writeback_dirty(struct address_space *mapping)
  {
  	return bdi_cap_writeback_dirty(inode_to_bdi(mapping->host));
  }
  
  static inline bool mapping_cap_account_dirty(struct address_space *mapping)
  {
  	return bdi_cap_account_dirty(inode_to_bdi(mapping->host));
  }
  
  static inline int bdi_sched_wait(void *word)
  {
  	schedule();
  	return 0;
  }
  
  #ifdef CONFIG_CGROUP_WRITEBACK
  
  struct bdi_writeback_congested *
  wb_congested_get_create(struct backing_dev_info *bdi, int blkcg_id, gfp_t gfp);
  void wb_congested_put(struct bdi_writeback_congested *congested);
  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 blkcg *blkcg);
  int inode_congested(struct inode *inode, int cong_bits);
  
  /**
   * inode_cgwb_enabled - test whether cgroup writeback is enabled on an inode
   * @inode: inode of interest
   *
   * cgroup writeback requires support from both the bdi and 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_cap_account_dirty(bdi) &&
  		(bdi->capabilities & BDI_CAP_CGROUP_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_is_valid - test whether an inode has a wb associated
   * @inode: inode of interest
   *
   * Returns %true if @inode has a wb associated.  May be called without any
   * locking.
   */
  static inline bool inode_to_wb_is_valid(struct inode *inode)
  {
  	return inode->i_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;
  }
  
  /**
   * 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_congested *
  wb_congested_get_create(struct backing_dev_info *bdi, int blkcg_id, gfp_t gfp)
  {
  	refcount_inc(&bdi->wb_congested->refcnt);
  	return bdi->wb_congested;
  }
  
  static inline void wb_congested_put(struct bdi_writeback_congested *congested)
  {
  	if (refcount_dec_and_test(&congested->refcnt))
  		kfree(congested);
  }
  
  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 bool inode_to_wb_is_valid(struct inode *inode)
  {
  	return true;
  }
  
  static inline struct bdi_writeback *inode_to_wb(struct inode *inode)
  {
  	return &inode_to_bdi(inode)->wb;
  }
  
  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 blkcg *blkcg)
  {
  }
  
  static inline int inode_congested(struct inode *inode, int cong_bits)
  {
  	return wb_congested(&inode_to_bdi(inode)->wb, cong_bits);
  }
  
  #endif	/* CONFIG_CGROUP_WRITEBACK */
  
  static inline int inode_read_congested(struct inode *inode)
  {
  	return inode_congested(inode, 1 << WB_sync_congested);
  }
  
  static inline int inode_write_congested(struct inode *inode)
  {
  	return inode_congested(inode, 1 << WB_async_congested);
  }
  
  static inline int inode_rw_congested(struct inode *inode)
  {
  	return inode_congested(inode, (1 << WB_sync_congested) |
  				      (1 << WB_async_congested));
  }
  
  static inline int bdi_congested(struct backing_dev_info *bdi, int cong_bits)
  {
  	return wb_congested(&bdi->wb, cong_bits);
  }
  
  static inline int bdi_read_congested(struct backing_dev_info *bdi)
  {
  	return bdi_congested(bdi, 1 << WB_sync_congested);
  }
  
  static inline int bdi_write_congested(struct backing_dev_info *bdi)
  {
  	return bdi_congested(bdi, 1 << WB_async_congested);
  }
  
  static inline int bdi_rw_congested(struct backing_dev_info *bdi)
  {
  	return bdi_congested(bdi, (1 << WB_sync_congested) |
  				  (1 << WB_async_congested));
  }
  
  #endif	/* _LINUX_BACKING_DEV_H */
  