Re: [Xen-devel] [PATCH 1/2] xen/x86: return partial memory map in case of not enough space

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 05.12.16 at 17:34, <JGross@xxxxxxxx> wrote:
> For XENMEM_machine_memory_map the hypervisor returns EINVAL if the
> caller's buffer can't hold all entries.
> 
> This is a problem as the caller has normally a static buffer defined
> and when he is doing the call no dynamic memory allocation is
> possible as nothing is yet known about the system's memory layout.
> 
> Instead of just fail deliver as many memory map entries as possible
> and return with E2BIG indicating the result was incomplete. Then the
> caller will be capable to use at least some memory reported to exist
> to allocate a larger buffer for the complete memory map.

This makes no sense, as what we're talking about here is the
machine memory map, and the calling Dom0 kernel can't allocate
from that pool directly. Instead it would need its own memory
map to know where to place such a larger buffer, and this map
is usually just one or two entries large.

For that reason I'm not convinced we need or want this change.

Jan


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