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SubjectRe: Copy_to_user() and locks.
Hi,

On Tue, 8 Feb 2000 15:46:34 -0500 (EST), "Richard B. Johnson"
<root@chaos.analogic.com> said:

> You must not copy_to_user() under a lock. This is because the
> user's pages may not be in memory and the kernel needs to page-
> fault.

> Unfortunately, this often means that you have to copy twice, double
> buffer. However, a typical PC nowdays can copy over 800 megabytes per
> second.

Correct. However, what you _can_ do is to allocate kernel memory and
access that from your driver, and to map that same memory into user
space so that it is visible from a user process without copying.

--Stephen

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