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Message-Id: <11972545383139-git-send-email-ezk@cs.sunysb.edu> Date: Sun, 9 Dec 2007 21:41:38 -0500 From: Erez Zadok <ezk@...sunysb.edu> To: hch@...radead.org, viro@....linux.org.uk, akpm@...ux-foundation.org Cc: linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org, Erez Zadok <ezk@...sunysb.edu> Subject: [PATCH 05/42] Unionfs: documentation for any known issues Signed-off-by: Erez Zadok <ezk@...sunysb.edu> --- Documentation/filesystems/unionfs/issues.txt | 24 ++++++++++++++++++++++++ 1 files changed, 24 insertions(+), 0 deletions(-) create mode 100644 Documentation/filesystems/unionfs/issues.txt diff --git a/Documentation/filesystems/unionfs/issues.txt b/Documentation/filesystems/unionfs/issues.txt new file mode 100644 index 0000000..9db1d70 --- /dev/null +++ b/Documentation/filesystems/unionfs/issues.txt @@ -0,0 +1,24 @@ +KNOWN Unionfs 2.1 ISSUES: +========================= + +1. Unionfs should not use lookup_one_len() on the underlying f/s as it + confuses NFSv4. Currently, unionfs_lookup() passes lookup intents to the + lower file-system, this eliminates part of the problem. The remaining + calls to lookup_one_len may need to be changed to pass an intent. We are + currently introducing VFS changes to fs/namei.c's do_path_lookup() to + allow proper file lookup and opening in stackable file systems. + +2. Lockdep (a debugging feature) isn't aware of stacking, and so it + incorrectly complains about locking problems. The problem boils down to + this: Lockdep considers all objects of a certain type to be in the same + class, for example, all inodes. Lockdep doesn't like to see a lock held + on two inodes within the same task, and warns that it could lead to a + deadlock. However, stackable file systems do precisely that: they lock + an upper object, and then a lower object, in a strict order to avoid + locking problems; in addition, Unionfs, as a fan-out file system, may + have to lock several lower inodes. We are currently looking into Lockdep + to see how to make it aware of stackable file systems. In the meantime, + if you get any warnings from Lockdep, you can safely ignore them (or feel + free to report them to the Unionfs maintainers, just to be sure). + +For more information, see <http://unionfs.filesystems.org/>. -- 1.5.2.2 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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