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 /* SPDX-License-Identifier: GPL-2.0 */
 #ifndef __LINUX_DCACHE_H
 #define __LINUX_DCACHE_H
 
 #include <linux/atomic.h>
 #include <linux/list.h>
 #include <linux/math.h>
 #include <linux/rculist.h>
 #include <linux/rculist_bl.h>
 #include <linux/spinlock.h>
 #include <linux/seqlock.h>
 #include <linux/cache.h>
 #include <linux/rcupdate.h>
 #include <linux/lockref.h>
 #include <linux/stringhash.h>
 #include <linux/wait.h>
 
 struct path;
 struct vfsmount;
 
 /*
  * linux/include/linux/dcache.h
  *
  * Dirent cache data structures
  *
  * (C) Copyright 1997 Thomas Schoebel-Theuer,
  * with heavy changes by Linus Torvalds
  */
 
 #define IS_ROOT(x) ((x) == (x)->d_parent)
 
 /* The hash is always the low bits of hash_len */
 #ifdef __LITTLE_ENDIAN
  #define HASH_LEN_DECLARE u32 hash; u32 len
  #define bytemask_from_count(cnt)   (~(~0ul << (cnt)*8))
 #else
  #define HASH_LEN_DECLARE u32 len; u32 hash
  #define bytemask_from_count(cnt)   (~(~0ul >> (cnt)*8))
 #endif
 
 /*
  * "quick string" -- eases parameter passing, but more importantly
  * saves "metadata" about the string (ie length and the hash).
  *
  * hash comes first so it snuggles against d_parent in the
  * dentry.
  */
 struct qstr {
     union {
         struct {
             HASH_LEN_DECLARE;
         };
         u64 hash_len;
     };
     const unsigned char *name;
 };
 
 #define QSTR_INIT(n,l) { { { .len = l } }, .name = n }
 
 extern const struct qstr empty_name;
 extern const struct qstr slash_name;
 extern const struct qstr dotdot_name;
 
 /*
  * Try to keep struct dentry aligned on 64 byte cachelines (this will
  * give reasonable cacheline footprint with larger lines without the
  * large memory footprint increase).
  */
 #ifdef CONFIG_64BIT
 # define DNAME_INLINE_LEN 32 /* 192 bytes */
 #else
 # ifdef CONFIG_SMP
 #  define DNAME_INLINE_LEN 36 /* 128 bytes */
 # else
 #  define DNAME_INLINE_LEN 40 /* 128 bytes */
 # endif
 #endif
 
 #define d_lock  d_lockref.lock
 
 struct dentry {
     /* RCU lookup touched fields */
     unsigned int d_flags;       /* protected by d_lock */
     seqcount_spinlock_t d_seq;  /* per dentry seqlock */
     struct hlist_bl_node d_hash;    /* lookup hash list */
     struct dentry *d_parent;    /* parent directory */
     struct qstr d_name;
     struct inode *d_inode;      /* Where the name belongs to - NULL is
                      * negative */
     unsigned char d_iname[DNAME_INLINE_LEN];    /* small names */
 
     /* Ref lookup also touches following */
     struct lockref d_lockref;   /* per-dentry lock and refcount */
     const struct dentry_operations *d_op;
     struct super_block *d_sb;   /* The root of the dentry tree */
     unsigned long d_time;       /* used by d_revalidate */
     void *d_fsdata;         /* fs-specific data */
 
     union {
         struct list_head d_lru;     /* LRU list */
         wait_queue_head_t *d_wait;  /* in-lookup ones only */
     };
     struct list_head d_child;   /* child of parent list */
     struct list_head d_subdirs; /* our children */
     /*
      * d_alias and d_rcu can share memory
      */
     union {
         struct hlist_node d_alias;  /* inode alias list */
         struct hlist_bl_node d_in_lookup_hash;  /* only for in-lookup ones */
         struct rcu_head d_rcu;
     } d_u;
 } __randomize_layout;
 
 /*
  * dentry->d_lock spinlock nesting subclasses:
  *
  * 0: normal
  * 1: nested
  */
 enum dentry_d_lock_class
 {
     DENTRY_D_LOCK_NORMAL, /* implicitly used by plain spin_lock() APIs. */
     DENTRY_D_LOCK_NESTED
 };
 
 struct dentry_operations {
     int (*d_revalidate)(struct dentry *, unsigned int);
     int (*d_weak_revalidate)(struct dentry *, unsigned int);
     int (*d_hash)(const struct dentry *, struct qstr *);
     int (*d_compare)(const struct dentry *,
             unsigned int, const char *, const struct qstr *);
     int (*d_delete)(const struct dentry *);
     int (*d_init)(struct dentry *);
     void (*d_release)(struct dentry *);
     void (*d_prune)(struct dentry *);
     void (*d_iput)(struct dentry *, struct inode *);
     char *(*d_dname)(struct dentry *, char *, int);
     struct vfsmount *(*d_automount)(struct path *);
     int (*d_manage)(const struct path *, bool);
     struct dentry *(*d_real)(struct dentry *, const struct inode *);
 } ____cacheline_aligned;
 
 /*
  * Locking rules for dentry_operations callbacks are to be found in
  * Documentation/filesystems/locking.rst. Keep it updated!
  *
  * FUrther descriptions are found in Documentation/filesystems/vfs.rst.
  * Keep it updated too!
  */
 
 /* d_flags entries */
 #define DCACHE_OP_HASH          0x00000001
 #define DCACHE_OP_COMPARE       0x00000002
 #define DCACHE_OP_REVALIDATE        0x00000004
 #define DCACHE_OP_DELETE        0x00000008
 #define DCACHE_OP_PRUNE         0x00000010
 
 #define DCACHE_DISCONNECTED     0x00000020
      /* This dentry is possibly not currently connected to the dcache tree, in
       * which case its parent will either be itself, or will have this flag as
       * well.  nfsd will not use a dentry with this bit set, but will first
       * endeavour to clear the bit either by discovering that it is connected,
       * or by performing lookup operations.   Any filesystem which supports
       * nfsd_operations MUST have a lookup function which, if it finds a
       * directory inode with a DCACHE_DISCONNECTED dentry, will d_move that
       * dentry into place and return that dentry rather than the passed one,
       * typically using d_splice_alias. */
 
 #define DCACHE_REFERENCED       0x00000040 /* Recently used, don't discard. */
 
 #define DCACHE_DONTCACHE        0x00000080 /* Purge from memory on final dput() */
 
 #define DCACHE_CANT_MOUNT       0x00000100
 #define DCACHE_GENOCIDE         0x00000200
 #define DCACHE_SHRINK_LIST      0x00000400
 
 #define DCACHE_OP_WEAK_REVALIDATE   0x00000800
 
 #define DCACHE_NFSFS_RENAMED        0x00001000
      /* this dentry has been "silly renamed" and has to be deleted on the last
       * dput() */
 #define DCACHE_COOKIE           0x00002000 /* For use by dcookie subsystem */
 #define DCACHE_FSNOTIFY_PARENT_WATCHED  0x00004000
      /* Parent inode is watched by some fsnotify listener */
 
 #define DCACHE_DENTRY_KILLED        0x00008000
 
 #define DCACHE_MOUNTED          0x00010000 /* is a mountpoint */
 #define DCACHE_NEED_AUTOMOUNT       0x00020000 /* handle automount on this dir */
 #define DCACHE_MANAGE_TRANSIT       0x00040000 /* manage transit from this dirent */
 #define DCACHE_MANAGED_DENTRY \
     (DCACHE_MOUNTED|DCACHE_NEED_AUTOMOUNT|DCACHE_MANAGE_TRANSIT)
 
 #define DCACHE_LRU_LIST         0x00080000
 
 #define DCACHE_ENTRY_TYPE       0x00700000
 #define DCACHE_MISS_TYPE        0x00000000 /* Negative dentry (maybe fallthru to nowhere) */
 #define DCACHE_WHITEOUT_TYPE        0x00100000 /* Whiteout dentry (stop pathwalk) */
 #define DCACHE_DIRECTORY_TYPE       0x00200000 /* Normal directory */
 #define DCACHE_AUTODIR_TYPE     0x00300000 /* Lookupless directory (presumed automount) */
 #define DCACHE_REGULAR_TYPE     0x00400000 /* Regular file type (or fallthru to such) */
 #define DCACHE_SPECIAL_TYPE     0x00500000 /* Other file type (or fallthru to such) */
 #define DCACHE_SYMLINK_TYPE     0x00600000 /* Symlink (or fallthru to such) */
 
 #define DCACHE_MAY_FREE         0x00800000
 #define DCACHE_FALLTHRU         0x01000000 /* Fall through to lower layer */
 #define DCACHE_NOKEY_NAME       0x02000000 /* Encrypted name encoded without key */
 #define DCACHE_OP_REAL          0x04000000
 
 #define DCACHE_PAR_LOOKUP       0x10000000 /* being looked up (with parent locked shared) */
 #define DCACHE_DENTRY_CURSOR        0x20000000
 #define DCACHE_NORCU            0x40000000 /* No RCU delay for freeing */
 
 extern seqlock_t rename_lock;
 
 /*
  * These are the low-level FS interfaces to the dcache..
  */
 extern void d_instantiate(struct dentry *, struct inode *);
 extern void d_instantiate_new(struct dentry *, struct inode *);
 extern struct dentry * d_instantiate_unique(struct dentry *, struct inode *);
 extern struct dentry * d_instantiate_anon(struct dentry *, struct inode *);
 extern void __d_drop(struct dentry *dentry);
 extern void d_drop(struct dentry *dentry);
 extern void d_delete(struct dentry *);
 extern void d_set_d_op(struct dentry *dentry, const struct dentry_operations *op);
 
 /* allocate/de-allocate */
 extern struct dentry * d_alloc(struct dentry *, const struct qstr *);
 extern struct dentry * d_alloc_anon(struct super_block *);
 extern struct dentry * d_alloc_parallel(struct dentry *, const struct qstr *,
                     wait_queue_head_t *);
 extern struct dentry * d_splice_alias(struct inode *, struct dentry *);
 extern struct dentry * d_add_ci(struct dentry *, struct inode *, struct qstr *);
 extern bool d_same_name(const struct dentry *dentry, const struct dentry *parent,
             const struct qstr *name);
 extern struct dentry * d_exact_alias(struct dentry *, struct inode *);
 extern struct dentry *d_find_any_alias(struct inode *inode);
 extern struct dentry * d_obtain_alias(struct inode *);
 extern struct dentry * d_obtain_root(struct inode *);
 extern void shrink_dcache_sb(struct super_block *);
 extern void shrink_dcache_parent(struct dentry *);
 extern void shrink_dcache_for_umount(struct super_block *);
 extern void d_invalidate(struct dentry *);
 
 /* only used at mount-time */
 extern struct dentry * d_make_root(struct inode *);
 
 /* <clickety>-<click> the ramfs-type tree */
 extern void d_genocide(struct dentry *);
 
 extern void d_tmpfile(struct dentry *, struct inode *);
 
 extern struct dentry *d_find_alias(struct inode *);
 extern void d_prune_aliases(struct inode *);
 
 extern struct dentry *d_find_alias_rcu(struct inode *);
 
 /* test whether we have any submounts in a subdir tree */
 extern int path_has_submounts(const struct path *);
 
 /*
  * This adds the entry to the hash queues.
  */
 extern void d_rehash(struct dentry *);
  
 extern void d_add(struct dentry *, struct inode *);
 
 /* used for rename() and baskets */
 extern void d_move(struct dentry *, struct dentry *);
 extern void d_exchange(struct dentry *, struct dentry *);
 extern struct dentry *d_ancestor(struct dentry *, struct dentry *);
 
 /* appendix may either be NULL or be used for transname suffixes */
 extern struct dentry *d_lookup(const struct dentry *, const struct qstr *);
 extern struct dentry *d_hash_and_lookup(struct dentry *, struct qstr *);
 extern struct dentry *__d_lookup(const struct dentry *, const struct qstr *);
 extern struct dentry *__d_lookup_rcu(const struct dentry *parent,
                 const struct qstr *name, unsigned *seq);
 
 static inline unsigned d_count(const struct dentry *dentry)
 {
     return dentry->d_lockref.count;
 }
 
 /*
  * helper function for dentry_operations.d_dname() members
  */
 extern __printf(4, 5)
 char *dynamic_dname(struct dentry *, char *, int, const char *, ...);
 
 extern char *__d_path(const struct path *, const struct path *, char *, int);
 extern char *d_absolute_path(const struct path *, char *, int);
 extern char *d_path(const struct path *, char *, int);
 extern char *dentry_path_raw(const struct dentry *, char *, int);
 extern char *dentry_path(const struct dentry *, char *, int);
 
 /* Allocation counts.. */
 
 /**
  *  dget, dget_dlock -  get a reference to a dentry
  *  @dentry: dentry to get a reference to
  *
  *  Given a dentry or %NULL pointer increment the reference count
  *  if appropriate and return the dentry. A dentry will not be 
  *  destroyed when it has references.
  */
 static inline struct dentry *dget_dlock(struct dentry *dentry)
 {
     if (dentry)
         dentry->d_lockref.count++;
     return dentry;
 }
 
 static inline struct dentry *dget(struct dentry *dentry)
 {
     if (dentry)
         lockref_get(&dentry->d_lockref);
     return dentry;
 }
 
 extern struct dentry *dget_parent(struct dentry *dentry);
 
 /**
  *  d_unhashed -    is dentry hashed
  *  @dentry: entry to check
  *
  *  Returns true if the dentry passed is not currently hashed.
  */
  
 static inline int d_unhashed(const struct dentry *dentry)
 {
     return hlist_bl_unhashed(&dentry->d_hash);
 }
 
 static inline int d_unlinked(const struct dentry *dentry)
 {
     return d_unhashed(dentry) && !IS_ROOT(dentry);
 }
 
 static inline int cant_mount(const struct dentry *dentry)
 {
     return (dentry->d_flags & DCACHE_CANT_MOUNT);
 }
 
 static inline void dont_mount(struct dentry *dentry)
 {
     spin_lock(&dentry->d_lock);
     dentry->d_flags |= DCACHE_CANT_MOUNT;
     spin_unlock(&dentry->d_lock);
 }
 
 extern void __d_lookup_unhash_wake(struct dentry *dentry);
 
 static inline int d_in_lookup(const struct dentry *dentry)
 {
     return dentry->d_flags & DCACHE_PAR_LOOKUP;
 }
 
 static inline void d_lookup_done(struct dentry *dentry)
 {
     if (unlikely(d_in_lookup(dentry)))
         __d_lookup_unhash_wake(dentry);
 }
 
 extern void dput(struct dentry *);
 
 static inline bool d_managed(const struct dentry *dentry)
 {
     return dentry->d_flags & DCACHE_MANAGED_DENTRY;
 }
 
 static inline bool d_mountpoint(const struct dentry *dentry)
 {
     return dentry->d_flags & DCACHE_MOUNTED;
 }
 
 /*
  * Directory cache entry type accessor functions.
  */
 static inline unsigned __d_entry_type(const struct dentry *dentry)
 {
     return dentry->d_flags & DCACHE_ENTRY_TYPE;
 }
 
 static inline bool d_is_miss(const struct dentry *dentry)
 {
     return __d_entry_type(dentry) == DCACHE_MISS_TYPE;
 }
 
 static inline bool d_is_whiteout(const struct dentry *dentry)
 {
     return __d_entry_type(dentry) == DCACHE_WHITEOUT_TYPE;
 }
 
 static inline bool d_can_lookup(const struct dentry *dentry)
 {
     return __d_entry_type(dentry) == DCACHE_DIRECTORY_TYPE;
 }
 
 static inline bool d_is_autodir(const struct dentry *dentry)
 {
     return __d_entry_type(dentry) == DCACHE_AUTODIR_TYPE;
 }
 
 static inline bool d_is_dir(const struct dentry *dentry)
 {
     return d_can_lookup(dentry) || d_is_autodir(dentry);
 }
 
 static inline bool d_is_symlink(const struct dentry *dentry)
 {
     return __d_entry_type(dentry) == DCACHE_SYMLINK_TYPE;
 }
 
 static inline bool d_is_reg(const struct dentry *dentry)
 {
     return __d_entry_type(dentry) == DCACHE_REGULAR_TYPE;
 }
 
 static inline bool d_is_special(const struct dentry *dentry)
 {
     return __d_entry_type(dentry) == DCACHE_SPECIAL_TYPE;
 }
 
 static inline bool d_is_file(const struct dentry *dentry)
 {
     return d_is_reg(dentry) || d_is_special(dentry);
 }
 
 static inline bool d_is_negative(const struct dentry *dentry)
 {
     // TODO: check d_is_whiteout(dentry) also.
     return d_is_miss(dentry);
 }
 
 static inline bool d_flags_negative(unsigned flags)
 {
     return (flags & DCACHE_ENTRY_TYPE) == DCACHE_MISS_TYPE;
 }
 
 static inline bool d_is_positive(const struct dentry *dentry)
 {
     return !d_is_negative(dentry);
 }
 
 /**
  * d_really_is_negative - Determine if a dentry is really negative (ignoring fallthroughs)
  * @dentry: The dentry in question
  *
  * Returns true if the dentry represents either an absent name or a name that
  * doesn't map to an inode (ie. ->d_inode is NULL).  The dentry could represent
  * a true miss, a whiteout that isn't represented by a 0,0 chardev or a
  * fallthrough marker in an opaque directory.
  *
  * Note!  (1) This should be used *only* by a filesystem to examine its own
  * dentries.  It should not be used to look at some other filesystem's
  * dentries.  (2) It should also be used in combination with d_inode() to get
  * the inode.  (3) The dentry may have something attached to ->d_lower and the
  * type field of the flags may be set to something other than miss or whiteout.
  */
 static inline bool d_really_is_negative(const struct dentry *dentry)
 {
     return dentry->d_inode == NULL;
 }
 
 /**
  * d_really_is_positive - Determine if a dentry is really positive (ignoring fallthroughs)
  * @dentry: The dentry in question
  *
  * Returns true if the dentry represents a name that maps to an inode
  * (ie. ->d_inode is not NULL).  The dentry might still represent a whiteout if
  * that is represented on medium as a 0,0 chardev.
  *
  * Note!  (1) This should be used *only* by a filesystem to examine its own
  * dentries.  It should not be used to look at some other filesystem's
  * dentries.  (2) It should also be used in combination with d_inode() to get
  * the inode.
  */
 static inline bool d_really_is_positive(const struct dentry *dentry)
 {
     return dentry->d_inode != NULL;
 }
 
 static inline int simple_positive(const struct dentry *dentry)
 {
     return d_really_is_positive(dentry) && !d_unhashed(dentry);
 }
 
 extern void d_set_fallthru(struct dentry *dentry);
 
 static inline bool d_is_fallthru(const struct dentry *dentry)
 {
     return dentry->d_flags & DCACHE_FALLTHRU;
 }
 
 
 extern int sysctl_vfs_cache_pressure;
 
 static inline unsigned long vfs_pressure_ratio(unsigned long val)
 {
     return mult_frac(val, sysctl_vfs_cache_pressure, 100);
 }
 
 /**
  * d_inode - Get the actual inode of this dentry
  * @dentry: The dentry to query
  *
  * This is the helper normal filesystems should use to get at their own inodes
  * in their own dentries and ignore the layering superimposed upon them.
  */
 static inline struct inode *d_inode(const struct dentry *dentry)
 {
     return dentry->d_inode;
 }
 
 /**
  * d_inode_rcu - Get the actual inode of this dentry with READ_ONCE()
  * @dentry: The dentry to query
  *
  * This is the helper normal filesystems should use to get at their own inodes
  * in their own dentries and ignore the layering superimposed upon them.
  */
 static inline struct inode *d_inode_rcu(const struct dentry *dentry)
 {
     return READ_ONCE(dentry->d_inode);
 }
 
 /**
  * d_backing_inode - Get upper or lower inode we should be using
  * @upper: The upper layer
  *
  * This is the helper that should be used to get at the inode that will be used
  * if this dentry were to be opened as a file.  The inode may be on the upper
  * dentry or it may be on a lower dentry pinned by the upper.
  *
  * Normal filesystems should not use this to access their own inodes.
  */
 static inline struct inode *d_backing_inode(const struct dentry *upper)
 {
     struct inode *inode = upper->d_inode;
 
     return inode;
 }
 
 /**
  * d_backing_dentry - Get upper or lower dentry we should be using
  * @upper: The upper layer
  *
  * This is the helper that should be used to get the dentry of the inode that
  * will be used if this dentry were opened as a file.  It may be the upper
  * dentry or it may be a lower dentry pinned by the upper.
  *
  * Normal filesystems should not use this to access their own dentries.
  */
 static inline struct dentry *d_backing_dentry(struct dentry *upper)
 {
     return upper;
 }
 
 /**
  * d_real - Return the real dentry
  * @dentry: the dentry to query
  * @inode: inode to select the dentry from multiple layers (can be NULL)
  *
  * If dentry is on a union/overlay, then return the underlying, real dentry.
  * Otherwise return the dentry itself.
  *
  * See also: Documentation/filesystems/vfs.rst
  */
 static inline struct dentry *d_real(struct dentry *dentry,
                     const struct inode *inode)
 {
     if (unlikely(dentry->d_flags & DCACHE_OP_REAL))
         return dentry->d_op->d_real(dentry, inode);
     else
         return dentry;
 }
 
 /**
  * d_real_inode - Return the real inode
  * @dentry: The dentry to query
  *
  * If dentry is on a union/overlay, then return the underlying, real inode.
  * Otherwise return d_inode().
  */
 static inline struct inode *d_real_inode(const struct dentry *dentry)
 {
     /* This usage of d_real() results in const dentry */
     return d_backing_inode(d_real((struct dentry *) dentry, NULL));
 }
 
 struct name_snapshot {
     struct qstr name;
     unsigned char inline_name[DNAME_INLINE_LEN];
 };
 void take_dentry_name_snapshot(struct name_snapshot *, struct dentry *);
 void release_dentry_name_snapshot(struct name_snapshot *);
 
 #endif  /* __LINUX_DCACHE_H */

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