Re: [Xen-devel] [PATCH] libxc: refactor memory allocation functions

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Tue, Dec 01, 2015 at 01:04:14PM +0100, Juergen Gross wrote:
> On 01/12/15 12:58, Ian Campbell wrote:
> > On Tue, 2015-12-01 at 11:39 +0000, Wei Liu wrote:
> >> There were some problems with the original memory allocation functions:
> >> 1. xc_dom_alloc_segment and xc_dom_alloc_pad ended up calling
> >>    xc_dom_chk_alloc_pages while xc_dom_alloc_page open-coded everything.
> >> 2. xc_dom_alloc_pad didn't call dom->allocate.
> >>
> >> Refactor the code so that:
> >> 1. xc_dom_alloc_{segment,pad,page} end up calling
> >>    xc_dom_chk_alloc_pages.
> >> 2. xc_dom_chk_alloc_pages calls dom->allocate.
> >>
> >> This way we avoid scattering dom->allocate over multiple locations and
> >> open-coding.
> >>
> >> Also change the return type of xc_dom_alloc_page to xen_pfn_t and return
> >> an invalid pfn when xc_dom_chk_alloc_pages fails.
> > 
> > Given this presumably the handful of callers ought to gain some error
> > handling in a followup patch?
> 
> I could do that. Wei?
> 

You're welcome to pick that up.

> > 
> > xc_dom_chk_alloc_pages does log, so at least the callers needn't bother
> > with that.
> > 
> >> Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>
> > 
> > Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
> > 
> >> ---
> >> Cc: Ian Campbell <ian.campbell@xxxxxxxxxx>
> >> Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
> >> Cc: Juergen Gross <jgross@xxxxxxxx>
> >>
> >> We don't have INVALID_PFN, maybe we need one?
> > 
> > We have INVALID_MFN and INVALID_P2M_ENTRY, not sure if the latter fits the
> > bill (or if not how it is distinct from the former).
> 
> What about merging all of them into INVALID_FRAME?
> 

Note that INVALID_MFN is in public header (xenctrl.h) while
INVALID_P2M_ENTRY is not.

In fact (xen_pfn_t)-1 is part of guest ABI so we should properly export
and document it. The current situation is not ideal. Not sure how much
yak shaving is required though.

Wei.

> I can create a patch(-series).
> 
> 
> Juergen
> 

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