Messages in this thread | | | Date | Thu, 22 May 2003 02:46:24 +0200 | From | Carl-Daniel Hailfinger <> | Subject | Re: recursive spinlocks. Shoot. |
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Robert White wrote: > > Here is a problem statement that is virtually unimplementable in the current > Linux kernel because of the simple-minded locking model. > > Create a meta file-system that takes two existing (backing) file system > devices (or existing mounted directories) and aggregates them such that: > > (Ladies, and Gentlemen, The "deltafs" file system...)
Call it unionfs.
> 1) It doesn't matter what types of file systems are used as the backing file > systems. > 2) The aggregate file system is fully read-write > 3) The base (first existing) file system is read-only > 4) The front (second existing) file system is read-write > 5) All operations are available on the aggregate file system (unlink, > rename, open for write, open for append, chown, set access time, etc.) > 6) The aggregate file system engine will transcribe all the modified files > from the base to the front file system if the file is modified. > 7) The aggregate file system will (probably using a reserved file name and a > journaling structure encoded therein) maintain a white-out list to hide > unlinked and renamed files. > 8) After unmount, the front file system should be a minimal delta of the > base file system > 9) Remounting the same combination of file systems should consistently > result in the same, consistent file system image. > 10) (you get the point... 8-)
IIRC, Al Viro was working on this and we might have it in 2.6
http://www.ussg.iu.edu/hypermail/linux/kernel/0201.0/0745.html
Al?
Regards, Carl-Daniel
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