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Re: [PATCH v2 4/6] libxc: use multicall for memory-op on Linux (and Solaris)
- To: Jan Beulich <jbeulich@xxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Tue, 22 Jun 2021 20:35:18 +0100
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On 22/06/2021 16:19, Jan Beulich wrote:
> Some sub-functions, XENMEM_maximum_gpfn and XENMEM_maximum_ram_page in
> particular, can return values requiring more than 31 bits to represent.
> Hence we cannot issue the hypercall directly when the return value of
> ioctl() is used to propagate this value (note that this is not the case
> for the BSDs, and MiniOS already wraps all hypercalls in a multicall).
It took me 3 readings to realise you weren't saying that BSDs used
multicall (which they don't).
Instead, I'd suggest rewording it.
"Some sub-functions, XENMEM_maximum_gpfn and XENMEM_maximum_ram_page in
particular, can return values requiring more than 31 bits to represent.
The BSDs deliberately avoid using the ioctl() return value, and MiniOS
already uses a multicall. They aren't affected.
Linux and Solaris however do use the ioctl() return value, which must be
avoided in this case to avoid truncation."
Or something similar.
With a suitable improvement along these lines, Acked-by: Andrew Cooper
<andrew.cooper3@xxxxxxxxxx>
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