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vfs: add lookup_hash() helper

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Overlayfs needs lookup without inode_permission() and already has the name
hash (in form of dentry->d_name on overlayfs dentry).  It also doesn't
support filesystems with d_op->d_hash() so basically it only needs
the actual hashed lookup from lookup_one_len_unlocked()

So add a new helper that does unlocked lookup of a hashed name.

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
This commit is contained in:
Miklos Szeredi 2016-05-11 01:16:37 +02:00 committed by Al Viro
parent 9409e22acd
commit 3c9fe8cdff
2 changed files with 30 additions and 5 deletions
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33
fs/namei.c
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@ -2266,6 +2266,33 @@ int vfs_path_lookup(struct dentry *dentry, struct vfsmount *mnt,
}
EXPORT_SYMBOL(vfs_path_lookup);
/**
* lookup_hash - lookup single pathname component on already hashed name
* @name: name and hash to lookup
* @base: base directory to lookup from
*
* The name must have been verified and hashed (see lookup_one_len()). Using
* this after just full_name_hash() is unsafe.
*
* This function also doesn't check for search permission on base directory.
*
* Use lookup_one_len_unlocked() instead, unless you really know what you are
* doing.
*
* Do not hold i_mutex; this helper takes i_mutex if necessary.
*/
struct dentry *lookup_hash(const struct qstr *name, struct dentry *base)
{
struct dentry *ret;
ret = lookup_dcache(name, base, 0);
if (!ret)
ret = lookup_slow(name, base, 0);
return ret;
}
EXPORT_SYMBOL(lookup_hash);
/**
* lookup_one_len - filesystem helper to lookup single pathname component
* @name: pathname component to lookup
@ -2337,7 +2364,6 @@ struct dentry *lookup_one_len_unlocked(const char *name,
struct qstr this;
unsigned int c;
int err;
struct dentry *ret;
this.name = name;
this.len = len;
@ -2369,10 +2395,7 @@ struct dentry *lookup_one_len_unlocked(const char *name,
if (err)
return ERR_PTR(err);
ret = lookup_dcache(&this, base, 0);
if (!ret)
ret = lookup_slow(&this, base, 0);
return ret;
return lookup_hash(&this, base);
}
EXPORT_SYMBOL(lookup_one_len_unlocked);

2
include/linux/namei.h
View File

@ -79,6 +79,8 @@ extern int kern_path_mountpoint(int, const char *, struct path *, unsigned int);
extern struct dentry *lookup_one_len(const char *, struct dentry *, int);
extern struct dentry *lookup_one_len_unlocked(const char *, struct dentry *, int);
struct qstr;
extern struct dentry *lookup_hash(const struct qstr *, struct dentry *);
extern int follow_down_one(struct path *);
extern int follow_down(struct path *);