From mboxrd@z Thu Jan  1 00:00:00 1970
From: Tamas Lengyel <tamas.lengyel@zentific.com>
Subject: Re: Issues regarding "mem_access: Add helper API to
 setup ring and enable mem_access"
Date: Mon, 30 Jun 2014 14:06:24 +0200
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To: Ian Campbell <Ian.Campbell@citrix.com>
Cc: Aravindh Puthiyaparambil <aravindp@cisco.com>, Ian Jackson <Ian.Jackson@eu.citrix.com>, "xen-devel@lists.xen.org" <xen-devel@lists.xen.org>
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> > Now with this function being reintroduced, it becomes more complicated
> > to determine which version of the mem_access API does Xen actually
> > provide. A #define indicating mem_access API version would nicely
> > overcome this issue, or  naming xc_mem_event_enable something else.
>
> Doesn't configure support checking for functions with a given prototype?
>

It does but in a very hacky way, essentially trying to compile code where
the function is being called with different prototypes. We can work around
it but a clean solution would be preferred at some point.



> > Furthermore, the new xc_mem_event_enable function unconditionally
> > unpauses the VM. This may not be a desired behavior in all cases,
> > especially if the VM was in a paused state when the function was
> > called.
>
> domain pauses are referenced counted on the hypervisor side.
>

> Ian.
>
>
I did a quick test with xc_domain_pause being called twice, then
xc_domain_unpause once and the domain was in unpaused state at the end.
Same with the xen-access example, a paused domain gets automatically
unpaused by libxc, either though the xen-access code doesn't specifically
say it should be. This is now a rather opaque behavior of libxc. As it is
not merged into master I guess I will just submit a patch for it..

Tamas

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<div dir=3D"ltr"><br><div class=3D"gmail_extra"><div class=3D"gmail_quote">=
<blockquote class=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex;border-=
left:1px solid rgb(204,204,204);padding-left:1ex"><div>
&gt; Now with this function being reintroduced, it becomes more complicated=
<br>
&gt; to determine which version of the mem_access API does Xen actually<br>
&gt; provide. A #define indicating mem_access API version would nicely<br>
&gt; overcome this issue, or =C2=A0naming xc_mem_event_enable something els=
e.<br>
<br>
</div>Doesn&#39;t configure support checking for functions with a given pro=
totype?<br></blockquote><div><br></div><div>It does but in a very hacky way=
, essentially trying to compile code where the function is being called wit=
h different prototypes. We can work around it but a clean solution would be=
 preferred at some point.<br>

</div><div><br>=C2=A0</div><blockquote class=3D"gmail_quote" style=3D"margi=
n:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex=
">&gt; Furthermore, the new xc_mem_event_enable function unconditionally<br=
><div>


&gt; unpauses the VM. This may not be a desired behavior in all cases,<br>
&gt; especially if the VM was in a paused state when the function was<br>
&gt; called.<br>
<br>
</div>domain pauses are referenced counted on the hypervisor side. <br></bl=
ockquote><blockquote class=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8e=
x;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<span><font color=3D"#888888"><br>
Ian.<br>
<br></font></span></blockquote><div><br>I did a quick test with xc_domain_p=
ause being called twice, then xc_domain_unpause once and the domain was in =
unpaused state at the end. Same with the xen-access example, a paused domai=
n gets automatically unpaused by libxc, either though the xen-access code d=
oesn&#39;t specifically say it should be. This is now a rather opaque behav=
ior of libxc. As it is not merged into master I guess I will just submit a =
patch for it..<br>
<br></div>
<div>Tamas <br></div></div><br></div></div>

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