fs: add two trivial lookup helpers

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>

diff --git a/fs/namei.c b/fs/namei.c
index 3f1829b3ab5b7cda8e2a48071efd6ac23cff4bac..5f91d526a86e850e9dfe2de98781a80b4a1b68e5 100644 (file)
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2768,7 +2768,8 @@ struct dentry *lookup_one(struct user_namespace *mnt_userns, const char *name,
 EXPORT_SYMBOL(lookup_one);
 
 /**
- * lookup_one_len_unlocked - filesystem helper to lookup single pathname component
+ * 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
@@ -2779,14 +2780,15 @@ EXPORT_SYMBOL(lookup_one);
  * 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_len_unlocked(const char *name,
-                                      struct dentry *base, int len)
+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(&init_user_ns, name, base, len, &this);
+       err = lookup_one_common(mnt_userns, name, base, len, &this);
        if (err)
                return ERR_PTR(err);
 
@@ -2795,6 +2797,59 @@ struct dentry *lookup_one_len_unlocked(const char *name,
                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
+ * @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_len_unlocked(const char *name,
+                                      struct dentry *base, int len)
+{
+       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);
 

diff --git a/include/linux/namei.h b/include/linux/namei.h
index e89329bb3134e8b99add6f91db42b9bd3b33185c..caeb08a98536cc43b53652b4ab70d0adb99252c3 100644 (file)
--- a/include/linux/namei.h
+++ b/include/linux/namei.h
@@ -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 *);