Messages in this thread | | | From | "Josef 'Jeff' Sipek" <> | Subject | [PATCH 0/4] [RFC] New path lookup function | Date | Sat, 5 May 2007 19:09:30 -0400 |
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Stackable file systems, among others, frequently need to lookup paths or path components starting from an arbitrary point in the namespace (identified by a dentry and a vfsmount). Currently, such file systems use lookup_one_len, which is frowned upon [1] as it does not pass the lookup intent along; not passing a lookup intent, for example, can trigger BUG_ON's when stacking on top of NFSv4.
The first patch introduces a new lookup function to allow lookup starting from an arbitrary point in the namespace. This approach has been suggested by Christoph Hellwig [2].
The second patch changes sunrpc to use path_component_lookup.
The third patch changes nfsctl.c to use path_component_lookup.
The fourth, and last patch, unexports path_walk because it is no longer unnecessary to call it directly, and using the new path_component_lookup is cleaner.
For example, the following snippet of code, looks up "some/path/component" in a directory pointed to by parent_{dentry,vfsmnt}:
err = path_component_lookup(parent_dentry, parent_vfsmnt, "some/path/component", 0, &nd); if (!err) { /* exits */
...
/* once done, release the references */ path_release(&nd); } else if (err == -ENOENT) { /* doesn't exist */ } else { /* other error */ }
VFS functions such as lookup_create can be used on the nameidata structure to pass the create intent to the file system.
Currently, there is no easy way to pass the LOOKUP_OPEN intent. The proper way would be to call open_namei.
We'd like to get comments about what's necessary to make stackable file systems do lookups right: this includes potential changes to open_namei.
Josef 'Jeff' Sipek.
[1] http://lkml.org/lkml/2007/3/9/95 [2] http://lkml.org/lkml/2007/5/4/51
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