Re: getting some user memory

H. Peter Anvin (
3 Mar 1998 12:53:41 GMT

Followup to: <Pine.GSO.3.96.980228163432.16269A-100000@atle>
By author: Magnus Ahltorp <>
In newsgroup:
> I'm building a linux kernel module for arla, a free AFS client, and I'm
> having some problems with the directory caching. I have a userland daemon
> that serves me a cache file containing several directory entries.
> In the kernel, I call the i->i_op->default_file_ops->read() to read a
> block from the cache file, and then I walk through the block and do a
> filldir() call for each directory entry.
> The problem is that the "read" operation wants to write to user memory.
> I'm currently developing my things on a sparc, so I cheat by allocating
> kernel memory and let the read operation write to that memory, but that
> doesn't work on other archs.
> Is there some way of getting memory addressable as user space memory?

Use set_fs() to redirect "user memory" to kernel memory. This is used
in a number of places in the code. The name is a historical artifact
from when Linux used to use the i386 %fs register to point to user


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