Re: [Xen-devel] Front-end back-end connection

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Thu, 2011-10-13 at 12:31 +0100, Daniel Castro wrote:

> >> struct gnttab_setup_table gst;
> >>       grant_entries = (struct grant_entry_v1 *) get_grant_table();
> >>       gst.dom = DOMID_SELF;
> >>       gst.nr_frames = 1;
> >>       //gst.frame_list = (struct grant_entry_v1 *) grant_entries;
> >
> > This isn't needed? That would surprise me...
> Its part of the " OUT parameters. " in the struct, so I did not fill it out...

Isn't it the buffer to which the out parameters are written?

Maybe since you don't need to remap them in SeaBIOs (since the memory is
already mapped) it's actually irrelevant. On Linux e.g. this array
becomes the parameter to arch_gnttab_map_shared which actually maps the
pages.

> > However for simplicity I would suggest granting a static buffer to the
> > backend and copying from the SeaBIOS buffer to that.
> So would it be better to create another static buffer get a gref for
> it and copy from disk_op_s->buf_fl when reading and copy to when
> writing?

Not necessarily better, but simpler and sufficient for this use since it
avoids having to manage lots of grant references.

> BTW what are segments in SeaBIOS and whats the use for it? in Xen is
> only 32 Bit flat right? so I do not have to use any of the segment
> macros, right?

Segments are an X86-ism. You can find a chapter about that stuff in the
Intel Software Developer's Manual, I think. It's pretty early on.

All the code you are writing in SeaBIOS should, I think, be in the
32-bit flat part of SeaBIOS and so you don't need to worry about that.

Ian.



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