Re: [PATCH v5 6/9] libxc: create unmapped initrd in domain builder if supported

[Ian Campbell <ian.campbell@citrix.com>]

On Mon, 2015-11-30 at 12:03 +0100, Juergen Gross wrote:
> On 30/11/15 11:52, Ian Campbell wrote:
> > On Mon, 2015-11-30 at 10:51 +0000, Ian Campbell wrote:
> > > On Mon, 2015-11-30 at 11:47 +0100, Juergen Gross wrote:
> > > > On 30/11/15 11:34, Ian Campbell wrote:
> > > > > On Mon, 2015-11-30 at 11:23 +0100, Juergen Gross wrote:
> > > > > > On 30/11/15 11:20, Wei Liu wrote:
> > > > > > > On Thu, Nov 26, 2015 at 08:35:02AM +0100, Juergen Gross
> > > > > > > wrote:
> > > > > > > >  
> > > > > > > >      /* initrd parameters as specified in start_info page
> > > > > > > > */
> > > > > > > > -    unsigned long initrd_start;
> > > > > > > > -    unsigned long initrd_len;
> > > > > > > > +    uint64_t initrd_start;
> > > > > > > > +    uint64_t initrd_len;
> > > > > > > >  
> > > > > > > 
> > > > > > > I think these should be of type xen_vaddr_t. Doesn't make a
> > > > > > > difference
> > > > > > > in the end though.
> > > > > > 
> > > > > > xen_vaddr_t seems not to be appropriate. It can be either a
> > > > > > virtual
> > > > > > address or a pfn.
> > > > > 
> > > > > Did you mean a virtual address or a physical _address_?
> > > > > Potentially
> > > > > mixing
> > > > > addresses and frame numbers in a single variable seems liable to
> > > > > be
> > > > > confusing, at best.
> > > > 
> > > > No, it's really a pfn. And this is part of the stable interface
> > > > between
> > > > hypervisor and the pv-domU since more than 5 years now.
> > > 
> > > Including the virtual address bit?
> > > 
> > > That's a shame.
> > 
> > ... and that being the case would you mind adding a comment here
> > explaining
> > the two forms of these variables and the flag which indicates which one
> > is
> > "in force" at a given moment.
> 
> The comment in the struct already tells us that initrd_start and
> initrd_len are in the very same format as in the start_info page.
> Both fields are meant to be opaque to most of the domain builder
> parts.
> 
> The only function dealing with the differences is xc_dom_build_image()
> which already contains the appropriate flag. I added this on your
> request. You acked the resulting patch. So why do you want to add
> another comment now?

I hadn't realised at the time that the semantics of these fields was so,
uh, interesting.

Ian.


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