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

[Tamas Lengyel <tamas.lengyel@xxxxxxxxxxxx>]

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.

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.

Best,
Tamas

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