+/* copy of may_create in fs/namei.c() */
+static inline int btrfs_may_create(struct inode *dir, struct dentry *child)
+{
+ if (child->d_inode)
+ return -EEXIST;
+ if (IS_DEADDIR(dir))
+ return -ENOENT;
+ return inode_permission(dir, MAY_WRITE | MAY_EXEC);
+}
+
+/*
+ * Create a new subvolume below @parent. This is largely modeled after
+ * sys_mkdirat and vfs_mkdir, but we only do a single component lookup
+ * inside this filesystem so it's quite a bit simpler.
+ */
+static noinline int btrfs_mksubvol(struct path *parent, char *name,
+ int mode, int namelen)
+{
+ struct dentry *dentry;
+ int error;
+
+ mutex_lock_nested(&parent->dentry->d_inode->i_mutex, I_MUTEX_PARENT);
+
+ dentry = lookup_one_len(name, parent->dentry, namelen);
+ error = PTR_ERR(dentry);
+ if (IS_ERR(dentry))
+ goto out_unlock;
+
+ error = -EEXIST;
+ if (dentry->d_inode)
+ goto out_dput;
+
+ if (!IS_POSIXACL(parent->dentry->d_inode))
+ mode &= ~current->fs->umask;
+ error = mnt_want_write(parent->mnt);
+ if (error)
+ goto out_dput;
+
+ error = btrfs_may_create(parent->dentry->d_inode, dentry);
+ if (error)
+ goto out_drop_write;
+
+ mode &= (S_IRWXUGO|S_ISVTX);
+ error = security_inode_mkdir(parent->dentry->d_inode, dentry, mode);
+ if (error)
+ goto out_drop_write;
+
+ /*
+ * Actually perform the low-level subvolume creation after all
+ * this VFS fuzz.
+ *
+ * Eventually we want to pass in an inode under which we create this
+ * subvolume, but for now all are under the filesystem root.
+ *
+ * Also we should pass on the mode eventually to allow creating new
+ * subvolume with specific mode bits.
+ */
+ error = create_subvol(BTRFS_I(parent->dentry->d_inode)->root, dentry,
+ name, namelen);
+ if (error)
+ goto out_drop_write;
+
+ fsnotify_mkdir(parent->dentry->d_inode, dentry);
+out_drop_write:
+ mnt_drop_write(parent->mnt);
+out_dput:
+ dput(dentry);
+out_unlock:
+ mutex_unlock(&parent->dentry->d_inode->i_mutex);
+ return error;
+}
+
+