dcache.h

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#ifndef __LINUX_DCACHE_H
#define __LINUX_DCACHE_H

#include <linux/atomic.h>
#include <linux/list.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>

struct nameidata;
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;
#else
 #define HASH_LEN_DECLARE u32 len; u32 hash;
#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 }
#define hashlen_hash(hashlen) ((u32) (hashlen))
#define hashlen_len(hashlen)  ((u32)((hashlen) >> 32))

struct dentry_stat_t {
    int nr_dentry;
    int nr_unused;
    int age_limit;          /* age in seconds */
    int want_pages;         /* pages requested by system */
    int dummy[2];
};
extern struct dentry_stat_t dentry_stat;

/* Name hashing routines. Initial hash value */
/* Hash courtesy of the R5 hash in reiserfs modulo sign bits */
#define init_name_hash()        0

/* partial hash update function. Assume roughly 4 bits per character */
static inline unsigned long
partial_name_hash(unsigned long c, unsigned long prevhash)
{
    return (prevhash + (c << 4) + (c >> 4)) * 11;
}

/*
 * Finally: cut down the number of bits to a int value (and try to avoid
 * losing bits)
 */
static inline unsigned long end_name_hash(unsigned long hash)
{
    return (unsigned int) hash;
}

/* Compute the hash for a name string. */
extern unsigned int full_name_hash(const unsigned char *, unsigned int);

/*
 * 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

struct dentry {
    /* RCU lookup touched fields */
    unsigned int d_flags;       /* protected by d_lock */
    seqcount_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 */
    unsigned int d_count;       /* protected by d_lock */
    spinlock_t d_lock;      /* per dentry lock */
    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 */

    struct list_head d_lru;     /* LRU list */
    /*
     * d_child and d_rcu can share memory
     */
    union {
        struct list_head d_child;   /* child of parent list */
        struct rcu_head d_rcu;
    } d_u;
    struct list_head d_subdirs; /* our children */
    struct hlist_node d_alias;  /* inode alias list */
};

/*
 * 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_hash)(const struct dentry *, const struct inode *,
            struct qstr *);
    int (*d_compare)(const struct dentry *, const struct inode *,
            const struct dentry *, const struct inode *,
            unsigned int, const char *, const struct qstr *);
    int (*d_delete)(const 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)(struct dentry *, bool);
} ____cacheline_aligned;

/*
 * Locking rules for dentry_operations callbacks are to be found in
 * Documentation/filesystems/Locking. Keep it updated!
 *
 * FUrther descriptions are found in Documentation/filesystems/vfs.txt.
 * Keep it updated too!
 */

/* d_flags entries */
#define DCACHE_OP_HASH      0x0001
#define DCACHE_OP_COMPARE   0x0002
#define DCACHE_OP_REVALIDATE    0x0004
#define DCACHE_OP_DELETE    0x0008
#define DCACHE_OP_PRUNE         0x0010

#define DCACHE_DISCONNECTED 0x0020
     /* 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   0x0040  /* Recently used, don't discard. */
#define DCACHE_RCUACCESS    0x0080  /* Entry has ever been RCU-visible */

#define DCACHE_CANT_MOUNT   0x0100
#define DCACHE_GENOCIDE     0x0200
#define DCACHE_SHRINK_LIST  0x0400

#define DCACHE_NFSFS_RENAMED    0x1000
     /* this dentry has been "silly renamed" and has to be deleted on the last
      * dput() */
#define DCACHE_COOKIE       0x2000  /* For use by dcookie subsystem */
#define DCACHE_FSNOTIFY_PARENT_WATCHED 0x4000
     /* Parent inode is watched by some fsnotify listener */

#define DCACHE_MOUNTED      0x10000 /* is a mountpoint */
#define DCACHE_NEED_AUTOMOUNT   0x20000 /* handle automount on this dir */
#define DCACHE_MANAGE_TRANSIT   0x40000 /* manage transit from this dirent */
#define DCACHE_NEED_LOOKUP  0x80000 /* dentry requires i_op->lookup */
#define DCACHE_MANAGED_DENTRY \
    (DCACHE_MOUNTED|DCACHE_NEED_AUTOMOUNT|DCACHE_MANAGE_TRANSIT)

#define DCACHE_DENTRY_KILLED    0x100000

extern seqlock_t rename_lock;

static inline int dname_external(struct dentry *dentry)
{
    return dentry->d_name.name != dentry->d_iname;
}

/*
 * These are the low-level FS interfaces to the dcache..
 */
extern void d_instantiate(struct dentry *, struct inode *);
extern struct dentry * d_instantiate_unique(struct dentry *, struct inode *);
extern struct dentry * d_materialise_unique(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_pseudo(struct super_block *, const struct qstr *);
extern struct dentry * d_splice_alias(struct inode *, struct dentry *);
extern struct dentry * d_add_ci(struct dentry *, struct inode *, struct qstr *);
extern struct dentry *d_find_any_alias(struct inode *inode);
extern struct dentry * d_obtain_alias(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 int 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 struct dentry *d_find_alias(struct inode *);
extern void d_prune_aliases(struct inode *);

/* test whether we have any submounts in a subdir tree */
extern int have_submounts(struct dentry *);

/*
 * This adds the entry to the hash queues.
 */
extern void d_rehash(struct dentry *);

static inline void d_add(struct dentry *entry, struct inode *inode)
{
    d_instantiate(entry, inode);
    d_rehash(entry);
}

static inline struct dentry *d_add_unique(struct dentry *entry, struct inode *inode)
{
    struct dentry *res;

    res = d_instantiate_unique(entry, inode);
    d_rehash(res != NULL ? res : entry);
    return res;
}

extern void dentry_update_name_case(struct dentry *, struct qstr *);

/* used for rename() and baskets */
extern void d_move(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(struct dentry *, struct qstr *);
extern struct dentry *d_hash_and_lookup(struct dentry *, struct qstr *);
extern struct dentry *__d_lookup(struct dentry *, struct qstr *);
extern struct dentry *__d_lookup_rcu(const struct dentry *parent,
                const struct qstr *name,
                unsigned *seq, struct inode *inode);

static inline int __d_rcu_to_refcount(struct dentry *dentry, unsigned seq)
{
    int ret = 0;

    assert_spin_locked(&dentry->d_lock);
    if (!read_seqcount_retry(&dentry->d_seq, seq)) {
        ret = 1;
        dentry->d_count++;
    }

    return ret;
}

/* validate "insecure" dentry pointer */
extern int d_validate(struct dentry *, struct dentry *);

/*
 * helper function for dentry_operations.d_dname() members
 */
extern 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 *d_path_with_unreachable(const struct path *, char *, int);
extern char *dentry_path_raw(struct dentry *, char *, int);
extern char *dentry_path(struct dentry *, char *, int);

/* Allocation counts.. */

static inline struct dentry *dget_dlock(struct dentry *dentry)
{
    if (dentry)
        dentry->d_count++;
    return dentry;
}

static inline struct dentry *dget(struct dentry *dentry)
{
    if (dentry) {
        spin_lock(&dentry->d_lock);
        dget_dlock(dentry);
        spin_unlock(&dentry->d_lock);
    }
    return dentry;
}

extern struct dentry *dget_parent(struct dentry *dentry);

static inline int d_unhashed(struct dentry *dentry)
{
    return hlist_bl_unhashed(&dentry->d_hash);
}

static inline int d_unlinked(struct dentry *dentry)
{
    return d_unhashed(dentry) && !IS_ROOT(dentry);
}

static inline int cant_mount(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 dput(struct dentry *);

static inline bool d_managed(struct dentry *dentry)
{
    return dentry->d_flags & DCACHE_MANAGED_DENTRY;
}

static inline bool d_mountpoint(struct dentry *dentry)
{
    return dentry->d_flags & DCACHE_MOUNTED;
}

static inline bool d_need_lookup(struct dentry *dentry)
{
    return dentry->d_flags & DCACHE_NEED_LOOKUP;
}

extern void d_clear_need_lookup(struct dentry *dentry);

extern int sysctl_vfs_cache_pressure;

#endif  /* __LINUX_DCACHE_H */