Signed-off-by: Erez Zadok <ezk@xxxxxxxxxxxxx> --- Documentation/filesystems/unionfs/concepts.txt | 13 +++++++++++++ 1 files changed, 13 insertions(+), 0 deletions(-) diff --git a/Documentation/filesystems/unionfs/concepts.txt b/Documentation/filesystems/unionfs/concepts.txt index bed69bd..8d9a1c5 100644 --- a/Documentation/filesystems/unionfs/concepts.txt +++ b/Documentation/filesystems/unionfs/concepts.txt @@ -210,4 +210,17 @@ there's a lot of concurrent activity on both the upper and lower objects, for the same file(s). Lastly, this delayed time attribute detection is similar to how NFS clients operate (e.g., acregmin). +Finally, there is no way currently in Linux to prevent lower directories +from being moved around (i.e., topology changes); there's no way to prevent +modifications to directory sub-trees of whole file systems which are mounted +read-write. It is therefore possible for in-flight operations in unionfs to +take place, while a lower directory is being moved around. Therefore, if +you try to, say, create a new file in a directory through unionfs, while the +directory is being moved around directly, then the new file may get created +in the new location where that directory was moved to. This is a somewhat +similar behaviour in NFS: an NFS client could be creating a new file while +th NFS server is moving th directory around; the file will get successfully +created in the new location. (The one exception in unionfs is that if the +branch is marked read-only by unionfs, then a copyup will take place.) + For more information, see <http://unionfs.filesystems.org/>. -- 1.5.2.2 - To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
