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Re: [Xen-devel] Issues regarding "mem_access: Add helper API to setup ring and enable mem_access"

On Mon, 2014-06-23 at 18:31 +0200, Tamas Lengyel wrote:
> Hi everyone,
> commit 6ae2df93c277b4093b3e54c9606387
> d1ba6d10fe into xen-staging includes a new function in xenctrl.h,
> xc_mem_event_enable. This function name however has been used
> previously in xenctrl.h up till at least Xen 4.1.2 for a different
> purpose. We have been using autoconf to check which version of the
> mem_access API is available in Xen by checking if xc_mem_event_enable
> is available, signaling that the mem_access API is Xen 4.1 style, and
> for xc_mem_access_enable signaling 4.2+ style API. See
> https://github.com/bdpayne/libvmi/blob/master/configure.ac#L140 for
> more details.
> 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?

> 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.


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