From 3ab27746f6214d691a2506fcbfe9aa7b72ecbb7d Mon Sep 17 00:00:00 2001 From: Erez Zadok Date: Sun, 28 Oct 2007 20:24:34 -0400 Subject: [PATCH] Unionfs: update usage.txt documention Signed-off-by: Erez Zadok --- Documentation/filesystems/unionfs/usage.txt | 17 +++++++++++++++++ 1 file changed, 17 insertions(+) diff --git a/Documentation/filesystems/unionfs/usage.txt b/Documentation/filesystems/unionfs/usage.txt index d8c15de80db..a6b1aca1b2b 100644 --- a/Documentation/filesystems/unionfs/usage.txt +++ b/Documentation/filesystems/unionfs/usage.txt @@ -74,6 +74,23 @@ to read-write, and change /bar from read-write to read-only: # mount -t unionfs -o remount,mode=/foo=rw,mode=/bar=ro none MOUNTPOINT +Note: in Unionfs 2.x, you cannot set the leftmost branch to readonly because +then Unionfs won't have any writable place for copyups to take place. +Moreover, the VFS can get confused when it tries to modify something in a +file system mounted read-write, but isn't permitted to write to it. +Instead, you should set the whole union as readonly, as described above. +If, however, you must set the leftmost branch as readonly, perhaps so you +can get a snapshot of it at a point in time, then you should insert a new +writable top-level branch, and mark the one you want as readonly. This can +be accomplished as follows, assuming that /foo is your current leftmost +branch: + +# mount -t tmpfs -o size=NNN /new +# mount -t unionfs -o remount,add=/new,mode=/foo=ro none MOUNTPOINT + +# mount -t unionfs -o remount,del=/new,mode=/foo=rw none MOUNTPOINT + +# umount /new CACHE CONSISTENCY ================= -- 2.43.0