c2452f3278
struct dentry is one of the most critical structures in the kernel. So it's sad to see it going neglected. With CONFIG_PROFILING turned on (which is probably the common case at least for distros and kernel developers), sizeof(struct dcache) == 208 here (64-bit). This gives 19 objects per slab. I packed d_mounted into a hole, and took another 4 bytes off the inline name length to take the padding out from the end of the structure. This shinks it to 200 bytes. I could have gone the other way and increased the length to 40, but I'm aiming for a magic number, read on... I then got rid of the d_cookie pointer. This shrinks it to 192 bytes. Rant: why was this ever a good idea? The cookie system should increase its hash size or use a tree or something if lookups are a problem. Also the "fast dcookie lookups" in oprofile should be moved into the dcookie code -- how can oprofile possibly care about the dcookie_mutex? It gets dropped after get_dcookie() returns so it can't be providing any sort of protection. At 192 bytes, 21 objects fit into a 4K page, saving about 3MB on my system with ~140 000 entries allocated. 192 is also a multiple of 64, so we get nice cacheline alignment on 64 and 32 byte line systems -- any given dentry will now require 3 cachelines to touch all fields wheras previously it would require 4. I know the inline name size was chosen quite carefully, however with the reduction in cacheline footprint, it should actually be just about as fast to do a name lookup for a 36 character name as it was before the patch (and faster for other sizes). The memory footprint savings for names which are <= 32 or > 36 bytes long should more than make up for the memory cost for 33-36 byte names. Performance is a feature... Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
377 lines
11 KiB
C
377 lines
11 KiB
C
#ifndef __LINUX_DCACHE_H
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#define __LINUX_DCACHE_H
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#include <asm/atomic.h>
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#include <linux/list.h>
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#include <linux/rculist.h>
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#include <linux/spinlock.h>
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#include <linux/cache.h>
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#include <linux/rcupdate.h>
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struct nameidata;
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struct path;
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struct vfsmount;
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/*
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* linux/include/linux/dcache.h
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*
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* Dirent cache data structures
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*
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* (C) Copyright 1997 Thomas Schoebel-Theuer,
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* with heavy changes by Linus Torvalds
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*/
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#define IS_ROOT(x) ((x) == (x)->d_parent)
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/*
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* "quick string" -- eases parameter passing, but more importantly
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* saves "metadata" about the string (ie length and the hash).
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*
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* hash comes first so it snuggles against d_parent in the
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* dentry.
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*/
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struct qstr {
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unsigned int hash;
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unsigned int len;
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const unsigned char *name;
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};
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struct dentry_stat_t {
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int nr_dentry;
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int nr_unused;
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int age_limit; /* age in seconds */
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int want_pages; /* pages requested by system */
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int dummy[2];
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};
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extern struct dentry_stat_t dentry_stat;
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/* Name hashing routines. Initial hash value */
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/* Hash courtesy of the R5 hash in reiserfs modulo sign bits */
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#define init_name_hash() 0
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/* partial hash update function. Assume roughly 4 bits per character */
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static inline unsigned long
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partial_name_hash(unsigned long c, unsigned long prevhash)
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{
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return (prevhash + (c << 4) + (c >> 4)) * 11;
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}
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/*
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* Finally: cut down the number of bits to a int value (and try to avoid
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* losing bits)
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*/
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static inline unsigned long end_name_hash(unsigned long hash)
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{
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return (unsigned int) hash;
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}
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/* Compute the hash for a name string. */
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static inline unsigned int
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full_name_hash(const unsigned char *name, unsigned int len)
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{
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unsigned long hash = init_name_hash();
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while (len--)
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hash = partial_name_hash(*name++, hash);
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return end_name_hash(hash);
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}
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/*
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* Try to keep struct dentry aligned on 64 byte cachelines (this will
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* give reasonable cacheline footprint with larger lines without the
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* large memory footprint increase).
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*/
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#ifdef CONFIG_64BIT
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#define DNAME_INLINE_LEN_MIN 32 /* 192 bytes */
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#else
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#define DNAME_INLINE_LEN_MIN 40 /* 128 bytes */
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#endif
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struct dentry {
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atomic_t d_count;
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unsigned int d_flags; /* protected by d_lock */
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spinlock_t d_lock; /* per dentry lock */
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int d_mounted;
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struct inode *d_inode; /* Where the name belongs to - NULL is
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* negative */
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/*
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* The next three fields are touched by __d_lookup. Place them here
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* so they all fit in a cache line.
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*/
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struct hlist_node d_hash; /* lookup hash list */
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struct dentry *d_parent; /* parent directory */
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struct qstr d_name;
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struct list_head d_lru; /* LRU list */
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/*
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* d_child and d_rcu can share memory
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*/
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union {
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struct list_head d_child; /* child of parent list */
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struct rcu_head d_rcu;
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} d_u;
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struct list_head d_subdirs; /* our children */
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struct list_head d_alias; /* inode alias list */
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unsigned long d_time; /* used by d_revalidate */
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struct dentry_operations *d_op;
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struct super_block *d_sb; /* The root of the dentry tree */
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void *d_fsdata; /* fs-specific data */
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unsigned char d_iname[DNAME_INLINE_LEN_MIN]; /* small names */
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};
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/*
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* dentry->d_lock spinlock nesting subclasses:
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*
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* 0: normal
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* 1: nested
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*/
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enum dentry_d_lock_class
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{
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DENTRY_D_LOCK_NORMAL, /* implicitly used by plain spin_lock() APIs. */
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DENTRY_D_LOCK_NESTED
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};
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struct dentry_operations {
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int (*d_revalidate)(struct dentry *, struct nameidata *);
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int (*d_hash) (struct dentry *, struct qstr *);
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int (*d_compare) (struct dentry *, struct qstr *, struct qstr *);
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int (*d_delete)(struct dentry *);
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void (*d_release)(struct dentry *);
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void (*d_iput)(struct dentry *, struct inode *);
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char *(*d_dname)(struct dentry *, char *, int);
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};
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/* the dentry parameter passed to d_hash and d_compare is the parent
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* directory of the entries to be compared. It is used in case these
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* functions need any directory specific information for determining
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* equivalency classes. Using the dentry itself might not work, as it
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* might be a negative dentry which has no information associated with
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* it */
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/*
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locking rules:
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big lock dcache_lock d_lock may block
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d_revalidate: no no no yes
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d_hash no no no yes
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d_compare: no yes yes no
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d_delete: no yes no no
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d_release: no no no yes
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d_iput: no no no yes
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*/
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/* d_flags entries */
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#define DCACHE_AUTOFS_PENDING 0x0001 /* autofs: "under construction" */
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#define DCACHE_NFSFS_RENAMED 0x0002 /* this dentry has been "silly
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* renamed" and has to be
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* deleted on the last dput()
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*/
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#define DCACHE_DISCONNECTED 0x0004
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/* This dentry is possibly not currently connected to the dcache tree,
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* in which case its parent will either be itself, or will have this
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* flag as well. nfsd will not use a dentry with this bit set, but will
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* first endeavour to clear the bit either by discovering that it is
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* connected, or by performing lookup operations. Any filesystem which
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* supports nfsd_operations MUST have a lookup function which, if it finds
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* a directory inode with a DCACHE_DISCONNECTED dentry, will d_move
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* that dentry into place and return that dentry rather than the passed one,
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* typically using d_splice_alias.
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*/
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#define DCACHE_REFERENCED 0x0008 /* Recently used, don't discard. */
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#define DCACHE_UNHASHED 0x0010
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#define DCACHE_INOTIFY_PARENT_WATCHED 0x0020 /* Parent inode is watched */
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#define DCACHE_COOKIE 0x0040 /* For use by dcookie subsystem */
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extern spinlock_t dcache_lock;
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extern seqlock_t rename_lock;
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/**
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* d_drop - drop a dentry
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* @dentry: dentry to drop
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*
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* d_drop() unhashes the entry from the parent dentry hashes, so that it won't
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* be found through a VFS lookup any more. Note that this is different from
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* deleting the dentry - d_delete will try to mark the dentry negative if
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* possible, giving a successful _negative_ lookup, while d_drop will
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* just make the cache lookup fail.
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*
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* d_drop() is used mainly for stuff that wants to invalidate a dentry for some
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* reason (NFS timeouts or autofs deletes).
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*
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* __d_drop requires dentry->d_lock.
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*/
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static inline void __d_drop(struct dentry *dentry)
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{
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if (!(dentry->d_flags & DCACHE_UNHASHED)) {
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dentry->d_flags |= DCACHE_UNHASHED;
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hlist_del_rcu(&dentry->d_hash);
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}
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}
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static inline void d_drop(struct dentry *dentry)
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{
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spin_lock(&dcache_lock);
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spin_lock(&dentry->d_lock);
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__d_drop(dentry);
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spin_unlock(&dentry->d_lock);
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spin_unlock(&dcache_lock);
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}
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static inline int dname_external(struct dentry *dentry)
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{
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return dentry->d_name.name != dentry->d_iname;
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}
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/*
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* These are the low-level FS interfaces to the dcache..
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*/
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extern void d_instantiate(struct dentry *, struct inode *);
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extern struct dentry * d_instantiate_unique(struct dentry *, struct inode *);
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extern struct dentry * d_materialise_unique(struct dentry *, struct inode *);
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extern void d_delete(struct dentry *);
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/* allocate/de-allocate */
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extern struct dentry * d_alloc(struct dentry *, const struct qstr *);
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extern struct dentry * d_splice_alias(struct inode *, struct dentry *);
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extern struct dentry * d_add_ci(struct dentry *, struct inode *, struct qstr *);
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extern struct dentry * d_obtain_alias(struct inode *);
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extern void shrink_dcache_sb(struct super_block *);
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extern void shrink_dcache_parent(struct dentry *);
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extern void shrink_dcache_for_umount(struct super_block *);
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extern int d_invalidate(struct dentry *);
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/* only used at mount-time */
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extern struct dentry * d_alloc_root(struct inode *);
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/* <clickety>-<click> the ramfs-type tree */
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extern void d_genocide(struct dentry *);
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extern struct dentry *d_find_alias(struct inode *);
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extern void d_prune_aliases(struct inode *);
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/* test whether we have any submounts in a subdir tree */
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extern int have_submounts(struct dentry *);
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/*
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* This adds the entry to the hash queues.
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*/
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extern void d_rehash(struct dentry *);
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/**
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* d_add - add dentry to hash queues
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* @entry: dentry to add
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* @inode: The inode to attach to this dentry
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*
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* This adds the entry to the hash queues and initializes @inode.
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* The entry was actually filled in earlier during d_alloc().
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*/
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static inline void d_add(struct dentry *entry, struct inode *inode)
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{
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d_instantiate(entry, inode);
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d_rehash(entry);
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}
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/**
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* d_add_unique - add dentry to hash queues without aliasing
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* @entry: dentry to add
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* @inode: The inode to attach to this dentry
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*
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* This adds the entry to the hash queues and initializes @inode.
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* The entry was actually filled in earlier during d_alloc().
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*/
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static inline struct dentry *d_add_unique(struct dentry *entry, struct inode *inode)
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{
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struct dentry *res;
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res = d_instantiate_unique(entry, inode);
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d_rehash(res != NULL ? res : entry);
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return res;
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}
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/* used for rename() and baskets */
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extern void d_move(struct dentry *, struct dentry *);
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extern struct dentry *d_ancestor(struct dentry *, struct dentry *);
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/* appendix may either be NULL or be used for transname suffixes */
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extern struct dentry * d_lookup(struct dentry *, struct qstr *);
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extern struct dentry * __d_lookup(struct dentry *, struct qstr *);
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extern struct dentry * d_hash_and_lookup(struct dentry *, struct qstr *);
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/* validate "insecure" dentry pointer */
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extern int d_validate(struct dentry *, struct dentry *);
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/*
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* helper function for dentry_operations.d_dname() members
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*/
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extern char *dynamic_dname(struct dentry *, char *, int, const char *, ...);
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extern char *__d_path(const struct path *path, struct path *root, char *, int);
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extern char *d_path(const struct path *, char *, int);
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extern char *dentry_path(struct dentry *, char *, int);
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/* Allocation counts.. */
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/**
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* dget, dget_locked - get a reference to a dentry
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* @dentry: dentry to get a reference to
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*
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* Given a dentry or %NULL pointer increment the reference count
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* if appropriate and return the dentry. A dentry will not be
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* destroyed when it has references. dget() should never be
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* called for dentries with zero reference counter. For these cases
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* (preferably none, functions in dcache.c are sufficient for normal
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* needs and they take necessary precautions) you should hold dcache_lock
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* and call dget_locked() instead of dget().
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*/
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static inline struct dentry *dget(struct dentry *dentry)
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{
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if (dentry) {
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BUG_ON(!atomic_read(&dentry->d_count));
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atomic_inc(&dentry->d_count);
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}
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return dentry;
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}
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extern struct dentry * dget_locked(struct dentry *);
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/**
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* d_unhashed - is dentry hashed
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* @dentry: entry to check
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*
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* Returns true if the dentry passed is not currently hashed.
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*/
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static inline int d_unhashed(struct dentry *dentry)
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{
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return (dentry->d_flags & DCACHE_UNHASHED);
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}
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static inline struct dentry *dget_parent(struct dentry *dentry)
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{
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struct dentry *ret;
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spin_lock(&dentry->d_lock);
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ret = dget(dentry->d_parent);
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spin_unlock(&dentry->d_lock);
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return ret;
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}
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extern void dput(struct dentry *);
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static inline int d_mountpoint(struct dentry *dentry)
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{
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return dentry->d_mounted;
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}
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extern struct vfsmount *lookup_mnt(struct vfsmount *, struct dentry *);
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extern struct dentry *lookup_create(struct nameidata *nd, int is_dir);
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extern int sysctl_vfs_cache_pressure;
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#endif /* __LINUX_DCACHE_H */
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