Re: [PATCH] sysinfo: include availram field in sysinfo struct

[Cyrill Gorcunov]

On Fri, Jan 07, 2022 at 01:04:51PM +0100, Christian Brauner wrote:
> > 
> > Wait. The userspace may pass old structure here, and in result we
> > return incorrect layout which won't match old one, no? Old binary
> > code has no clue about this header update.
> 
> Yes, that won't work as done.
> 

Yup. When I've been developing struct prctl_mm_map I reserved
PR_SET_MM_MAP_SIZE opcode so userspace would be able to query
current structure size and provide memory slab needed to fit
running structure.

As far as I see we can cut off some space from padding (at the
end of the structure) though one need to make a precise check
that there is no alignment holes appear on different architectures
other than x86. This area is pretty sensitive.