After reading part of the Arla daemon code available at
http://www.stacken.kth.se/projekt/arla/, I feel it is a real good design.
The daemon code is a multi-threaded user process that does most of the job
and the kernel is an interface to VFS. They communicate with each other
via a character device.
But I am wondering if the performance is good since you sometimes have to
cross user-system boundary up to four times for a single read operations:
read() --> Arla daemon --> network --> install data into kernel
If the daemon can somehow reside entirely inside the kernel, like NFS
daemon, we can save those crossings. But the daemon is a multi-threaded
process and we have no kernel thread yet, so I do not know how to do
better if possible. Maybe all user filesystems have to live with this
limitation.
Any help is appreciated.
-Zhihui
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