Re: kiobuf using kernel pages
Keith Owens (kaos@ocs.com.au)
Fri, 12 Nov 1999 16:30:23 +1100
On Fri, 12 Nov 1999 02:03:39 +0000 (GMT),
"Stephen C. Tweedie" <sct@redhat.com> wrote:
>On Thu, 11 Nov 1999 08:55:54 -0800 (PST), Matt Robinson
><yakker@cthulhu.engr.sgi.com> said:
>> We agree it's a violation in the worst sense. :) The problem is there
>> was no good way to set AS_KERNEL without calling map_user_kiobuf() on
>> your own. Until such a scheme is put in place (which we believe will be
>> at some point soon), we put something in to make it work for us. It's
>> certainly better than a conditional check in map_user_kiobuf(). :)
>
>Umm, why do you need this at all? The caller is either file IO --- in
>which case you just do the map_user_kiobuf and pass that to the kiovec
>IO routine --- or it is kernel-originated IO, in which case you create a
>kiobuf of your own and just stuff it full of references to the kernel
>pages you want to read or write.
User I/O: sys_write->sd_raw_fops.write->sd_raw_write->sd_raw_rw
Kernel I/O: vmdump->sd_raw_fops.write->sd_raw_write->sd_raw_rw
In SGI's 2.2.13 patch, sd_raw_write allocates the kiobuf, sd_raw_rw
maps and unmaps it so sd_raw_rw has to know what type of pages are
being used. In my 2.3.26 version, sd_raw_write allocates, maps and
unmaps the kiobuf, sd_raw_rw just uses whatever pages are in the
kiobuf. My version sets up user or kernel mappings depending on the
filp, or it would if I knew how to complete map_kernel_kiobuf(). SCT
is redoing kiobuf mappings so I am waiting on that change.
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