Re: [PATCH v2 2/2] mmap-alloc: Include osdep.h before checking CONFIG_LINUX

[Eduardo Habkost]

On Mon, Mar 16, 2020 at 06:08:54PM +0000, Peter Maydell wrote:
> On Mon, 16 Mar 2020 at 17:51, Eduardo Habkost <address@hidden> wrote:
> > Yes, but both MAP_SYNC and MAP_SHARED_VALIDATE aren't available
> > if the host is not Linux.
> >
> > Defining MAP_SYNC to 0 on MIPS would restore the existing
> > behavior, so it seems like a reasonable step to fix the build
> > failure.  But not even printing a warning when the host doesn't
> > have MAP_SYNC (the existing behavior on MIPS and non-Linux) seems
> > wrong.
> 
> The usual approach is that if you don't have the Linux-specific
> feature available you quietly fall back to whatever the sensible
> behaviour is for when the feature isn't present. We definitely
> don't want to be printing warnings on non-Linux systems that
> are effectively just saying "you're not running Linux". Same goes
> for "host happens not to be running a bleeding-edge Linux kernel
> and this feature isn't available yet".

I don't think using pmem=on without MAP_SYNC is expected to be a
supported use case, is it?  If a use case is not supported, the
sensible behavior is to tell the user it is not supported.

-- 
Eduardo