vfs: add lookup_open()

Split out lookup + maybe create from do_last().  This is the part under i_mutex
protection.

The function is called lookup_open() and returns a filp even though the open
part is not used yet.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --git a/fs/namei.c b/fs/namei.c
index 285e62e..fad7117 100644 (file)
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2197,19 +2197,73 @@ static inline int open_to_namei_flags(int flag)
 }
 
 /*
+ * Lookup, maybe create and open the last component
+ *
+ * Must be called with i_mutex held on parent.
+ *
+ * Returns open file or NULL on success, error otherwise.  NULL means no open
+ * was performed, only lookup.
+ */
+static struct file *lookup_open(struct nameidata *nd, struct path *path,
+                               const struct open_flags *op,
+                               int *want_write, bool *created)
+{
+       struct dentry *dir = nd->path.dentry;
+       struct dentry *dentry;
+       int error;
+
+       *created = false;
+       dentry = lookup_hash(nd);
+       if (IS_ERR(dentry))
+               return ERR_CAST(dentry);
+
+       /* Negative dentry, just create the file */
+       if (!dentry->d_inode && (op->open_flag & O_CREAT)) {
+               umode_t mode = op->mode;
+               if (!IS_POSIXACL(dir->d_inode))
+                       mode &= ~current_umask();
+               /*
+                * This write is needed to ensure that a
+                * rw->ro transition does not occur between
+                * the time when the file is created and when
+                * a permanent write count is taken through
+                * the 'struct file' in nameidata_to_filp().
+                */
+               error = mnt_want_write(nd->path.mnt);
+               if (error)
+                       goto out_dput;
+               *want_write = 1;
+               *created = true;
+               error = security_path_mknod(&nd->path, dentry, mode, 0);
+               if (error)
+                       goto out_dput;
+               error = vfs_create(dir->d_inode, dentry, mode, nd);
+               if (error)
+                       goto out_dput;
+       }
+       path->dentry = dentry;
+       path->mnt = nd->path.mnt;
+       return NULL;
+
+out_dput:
+       dput(dentry);
+       return ERR_PTR(error);
+}
+
+/*
  * Handle the last step of open()
  */
 static struct file *do_last(struct nameidata *nd, struct path *path,
                            const struct open_flags *op, const char *pathname)
 {
        struct dentry *dir = nd->path.dentry;
-       struct dentry *dentry;
        int open_flag = op->open_flag;
        int will_truncate = open_flag & O_TRUNC;
        int want_write = 0;
        int acc_mode = op->acc_mode;
        struct file *filp;
        struct inode *inode;
+       bool created;
        int symlink_ok = 0;
        struct path save_parent = { .dentry = NULL, .mnt = NULL };
        bool retried = false;
@@ -2277,53 +2331,24 @@ static struct file *do_last(struct nameidata *nd, struct path *path,
 
 retry_lookup:
        mutex_lock(&dir->d_inode->i_mutex);
+       filp = lookup_open(nd, path, op, &want_write, &created);
+       mutex_unlock(&dir->d_inode->i_mutex);
 
-       dentry = lookup_hash(nd);
-       error = PTR_ERR(dentry);
-       if (IS_ERR(dentry)) {
-               mutex_unlock(&dir->d_inode->i_mutex);
-               goto exit;
-       }
-
-       path->dentry = dentry;
-       path->mnt = nd->path.mnt;
+       if (IS_ERR(filp))
+               goto out;
 
-       /* Negative dentry, just create the file */
-       if (!dentry->d_inode && (open_flag & O_CREAT)) {
-               umode_t mode = op->mode;
-               if (!IS_POSIXACL(dir->d_inode))
-                       mode &= ~current_umask();
-               /*
-                * This write is needed to ensure that a
-                * rw->ro transition does not occur between
-                * the time when the file is created and when
-                * a permanent write count is taken through
-                * the 'struct file' in nameidata_to_filp().
-                */
-               error = mnt_want_write(nd->path.mnt);
-               if (error)
-                       goto exit_mutex_unlock;
-               want_write = 1;
+       if (created) {
                /* Don't check for write permission, don't truncate */
                open_flag &= ~O_TRUNC;
                will_truncate = 0;
                acc_mode = MAY_OPEN;
-               error = security_path_mknod(&nd->path, dentry, mode, 0);
-               if (error)
-                       goto exit_mutex_unlock;
-               error = vfs_create(dir->d_inode, dentry, mode, nd);
-               if (error)
-                       goto exit_mutex_unlock;
-               mutex_unlock(&dir->d_inode->i_mutex);
-               dput(nd->path.dentry);
-               nd->path.dentry = dentry;
+               path_to_nameidata(path, nd);
                goto common;
        }
 
        /*
         * It already exists.
         */
-       mutex_unlock(&dir->d_inode->i_mutex);
        audit_inode(pathname, path->dentry);
 
        error = -EEXIST;
@@ -2432,8 +2457,6 @@ out:
        terminate_walk(nd);
        return filp;
 
-exit_mutex_unlock:
-       mutex_unlock(&dir->d_inode->i_mutex);
 exit_dput:
        path_put_conditional(path, nd);
 exit: