Cache Manager

[wwshen@eecs.umich.edu]

> get a callback. The normal use for a filesystem is mostly reads. In that case
> it's good to know that the file you are about to read is the same that on the
> other computers in your cell. The problem with mutiple writers to the same
> file is minimal. And it will be solved by locking.

   I am still not very clear about what you said. Could you tell me
more about the read. I remember you sent an email about this before
as follow

> No, many programs will get confused if files are changed while they
> are reading (or executing them) so the local programs will not see the 
> modifications before the file is closed.
> 

    I think there is some conflict between them according to my
understanding.

> The procedure is something like this: (simplified)
> 
>  - The application program does a syscall, (on a file from arla)
                                              ^^^^^^^^^^^^^^^^^^^^
 					      What does this mean?

>  - The syscall is interpreted by the kernel,

     So this is not implemented by you, right?

>  - The kernel find out on which filesystem the file is, (our filesystem is xfs)
 
     So this in not implemented by you, but you need to provide
some information to the kernel so that it can switch to the
appropriate filsystem, right? Where is this file and functions?


>  - The kernel calls a VFS-operation om that filesystem, (xfs)
>     (in most cases xfs already has the file in the local cache, but
>      let's say it doesn't)

      I think VFS is Virtual File System, which is used to reference
the file entries but independent on the low implementation. But I
dont know what is the difference between the VFS operation and vnode
operation. I think at the mount point there is a mount structre connecting
a list of vnode related to this mount point. Is that the function
xfs_mount doing? Again, how can kernel call the function in xfs_vfsops.c
and xfs_vnodeops.c. 

      Sorry for disturbing you so much and thank you very much for
all of your help.

Have a good weekend!
Wuwei