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fs: add two trivial lookup helpers

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Similar to the addition of lookup_one() add a version of
lookup_one_unlocked() and lookup_one_positive_unlocked() that take
idmapped mounts into account. This is required to port overlay to
support idmapped base layers.

Cc: <linux-fsdevel@vger.kernel.org>
Tested-by: Giuseppe Scrivano <gscrivan@redhat.com>
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
This commit is contained in:
Christian Brauner 2022-04-04 12:51:40 +02:00 committed by Miklos Szeredi
parent 3123109284
commit 00675017e0
2 changed files with 74 additions and 18 deletions
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86
fs/namei.c
View File

@ -2767,6 +2767,72 @@ struct dentry *lookup_one(struct user_namespace *mnt_userns, const char *name,
}
EXPORT_SYMBOL(lookup_one);
/**
* lookup_one_unlocked - filesystem helper to lookup single pathname component
* @mnt_userns: idmapping of the mount the lookup is performed from
* @name: pathname component to lookup
* @base: base directory to lookup from
* @len: maximum length @len should be interpreted to
*
* Note that this routine is purely a helper for filesystem usage and should
* not be called by generic code.
*
* Unlike lookup_one_len, it should be called without the parent
* i_mutex held, and will take the i_mutex itself if necessary.
*/
struct dentry *lookup_one_unlocked(struct user_namespace *mnt_userns,
const char *name, struct dentry *base,
int len)
{
struct qstr this;
int err;
struct dentry *ret;
err = lookup_one_common(mnt_userns, name, base, len, &this);
if (err)
return ERR_PTR(err);
ret = lookup_dcache(&this, base, 0);
if (!ret)
ret = lookup_slow(&this, base, 0);
return ret;
}
EXPORT_SYMBOL(lookup_one_unlocked);
/**
* lookup_one_positive_unlocked - filesystem helper to lookup single
* pathname component
* @mnt_userns: idmapping of the mount the lookup is performed from
* @name: pathname component to lookup
* @base: base directory to lookup from
* @len: maximum length @len should be interpreted to
*
* This helper will yield ERR_PTR(-ENOENT) on negatives. The helper returns
* known positive or ERR_PTR(). This is what most of the users want.
*
* Note that pinned negative with unlocked parent _can_ become positive at any
* time, so callers of lookup_one_unlocked() need to be very careful; pinned
* positives have >d_inode stable, so this one avoids such problems.
*
* Note that this routine is purely a helper for filesystem usage and should
* not be called by generic code.
*
* The helper should be called without i_mutex held.
*/
struct dentry *lookup_one_positive_unlocked(struct user_namespace *mnt_userns,
const char *name,
struct dentry *base, int len)
{
struct dentry *ret = lookup_one_unlocked(mnt_userns, name, base, len);
if (!IS_ERR(ret) && d_flags_negative(smp_load_acquire(&ret->d_flags))) {
dput(ret);
ret = ERR_PTR(-ENOENT);
}
return ret;
}
EXPORT_SYMBOL(lookup_one_positive_unlocked);
/**
* lookup_one_len_unlocked - filesystem helper to lookup single pathname component
* @name: pathname component to lookup
@ -2782,18 +2848,7 @@ EXPORT_SYMBOL(lookup_one);
struct dentry *lookup_one_len_unlocked(const char *name,
struct dentry *base, int len)
{
struct qstr this;
int err;
struct dentry *ret;
err = lookup_one_common(&init_user_ns, name, base, len, &this);
if (err)
return ERR_PTR(err);
ret = lookup_dcache(&this, base, 0);
if (!ret)
ret = lookup_slow(&this, base, 0);
return ret;
return lookup_one_unlocked(&init_user_ns, name, base, len);
}
EXPORT_SYMBOL(lookup_one_len_unlocked);
@ -2808,12 +2863,7 @@ EXPORT_SYMBOL(lookup_one_len_unlocked);
struct dentry *lookup_positive_unlocked(const char *name,
struct dentry *base, int len)
{
struct dentry *ret = lookup_one_len_unlocked(name, base, len);
if (!IS_ERR(ret) && d_flags_negative(smp_load_acquire(&ret->d_flags))) {
dput(ret);
ret = ERR_PTR(-ENOENT);
}
return ret;
return lookup_one_positive_unlocked(&init_user_ns, name, base, len);
}
EXPORT_SYMBOL(lookup_positive_unlocked);

6
include/linux/namei.h
View File

@ -69,6 +69,12 @@ extern struct dentry *lookup_one_len(const char *, struct dentry *, int);
extern struct dentry *lookup_one_len_unlocked(const char *, struct dentry *, int);
extern struct dentry *lookup_positive_unlocked(const char *, struct dentry *, int);
struct dentry *lookup_one(struct user_namespace *, const char *, struct dentry *, int);
struct dentry *lookup_one_unlocked(struct user_namespace *mnt_userns,
const char *name, struct dentry *base,
int len);
struct dentry *lookup_one_positive_unlocked(struct user_namespace *mnt_userns,
const char *name,
struct dentry *base, int len);
extern int follow_down_one(struct path *);
extern int follow_down(struct path *);