Re: Implement paging on the pci arbiter

[Joan Lledó]

Hi,

El 26/8/20 a les 17:01, Samuel Thibault ha escrit:
> I'm unsure if libpager will be useful actually, since all you need is
> to pass on a memory object clamped to the target physical memory. See
> gnumach's support for proxy memory object, which possibly is just
> enough.
> 
> Samuel
> 

I did a research on this and think I could implement file mapping in
libnetfs based on this old patch by Marcus Brinkmann:

https://lists.gnu.org/archive/html/bug-hurd/2001-10/msg00305.html

Thomas Bushnell BSG answered to that message saying

> You must promise the kernel that *any* change to the underlying data
> for the mapped object will never change except with you telling the
> kernel

Which makes sense, but it seems to me it should be OK to enable file
mapping in a net filesystem provided only memory proxy objects are used
for this, since each proxy will belong to a memory object that meets the
requirement of keeping the kernel updated on any change in the
underlying data.

So we can take the implementation of io_map from that patch, but adding
a check to ensure whatever returned by the user from netfs_get_filemap()
is a proxy object. Is there a way to check that?

With that, from the aribter side we only need to get the default pager
and create a proxy for each region file, with its boundaries and
permissions, and write an implementation of netfs_get_filemap which
returns the proper proxy for each request.

What do you think?

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