Re: [PATCH 1 of 2] block_page_mkwrite() Implementation V2

Chris Mason
2007-05-16T12:55:37Z

On Wed, May 16, 2007 at 08:09:19PM +0800, David Woodhouse wrote:
> On Wed, 2007-05-16 at 11:19 +0100, David Howells wrote:
> > The start and end points passed to block_prepare_write() delimit the region of
> > the page that is going to be modified. This means that prepare_write()
> > doesn't need to fill it in if the page is not up to date.
>
> Really? Is it _really_ going to be modified? Even if the pointer
> userspace gave to write() is bogus, and is going to fault half-way
> through the copy_from_user()?

This is why there are so many variations on copy_from_user that zero on
faults. One way or another, the prepare_write/commit_write pair are
responsible for filling it in.

-chris