Re: [PATCH v1 4/5] util: add qemu_get_host_physmem utility function

[Christian Ehrhardt <christian.ehrhardt@canonical.com>]

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On Fri, Jul 17, 2020 at 3:32 PM BALATON Zoltan <balaton@eik.bme.hu> wrote:

> On Fri, 17 Jul 2020, Alex Bennée wrote:
> > This will be used in a future patch. For POSIX systems _SC_PHYS_PAGES
> > isn't standardised but at least appears in the man pages for
> > Open/FreeBSD. The result is advisory so any users of it shouldn't just
> > fail if we can't work it out.
> >
> > The win32 stub currently returns 0 until someone with a Windows system
> > can develop and test a patch.
> >
> > Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
> > Cc: BALATON Zoltan <balaton@eik.bme.hu>
> > Cc: Christian Ehrhardt <christian.ehrhardt@canonical.com>
> > ---
> > include/qemu/osdep.h | 10 ++++++++++
> > util/oslib-posix.c   | 11 +++++++++++
> > util/oslib-win32.c   |  6 ++++++
> > 3 files changed, 27 insertions(+)
> >
> > diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
> > index 4841b5c6b5f..7ff209983e2 100644
> > --- a/include/qemu/osdep.h
> > +++ b/include/qemu/osdep.h
> > @@ -665,4 +665,14 @@ static inline void qemu_reset_optind(void)
> >  */
> > char *qemu_get_host_name(Error **errp);
> >
> > +/**
> > + * qemu_get_host_physmem:
> > + *
> > + * Operating system agnostiv way of querying host memory.
>
> Typo: agnostiv -> agnostic
>
> > + *
> > + * Returns amount of physical memory on the system. This is purely
> > + * advisery and may return 0 if we can't work it out.
> > + */
> > +size_t qemu_get_host_physmem(void);
> > +
> > #endif
> > diff --git a/util/oslib-posix.c b/util/oslib-posix.c
> > index 36bf8593f8c..d9da782b896 100644
> > --- a/util/oslib-posix.c
> > +++ b/util/oslib-posix.c
> > @@ -839,3 +839,14 @@ char *qemu_get_host_name(Error **errp)
> >
> >     return g_steal_pointer(&hostname);
> > }
> > +
> > +size_t qemu_get_host_physmem(void)
> > +{
> > +#ifdef _SC_PHYS_PAGES
> > +    long pages = sysconf(_SC_PHYS_PAGES);
> > +    if (pages > 0) {
> > +        return pages * qemu_real_host_page_size;
>
> The Linux man page warns that this product may overflow so maybe you could
> return pages here.
>

The caller might be even less aware of that than this function - so maybe
better handle it here.
How about handling overflows and cutting it to MiB before returning?


> > +    }
> > +#endif
> > +    return 0;
> > +}
> > diff --git a/util/oslib-win32.c b/util/oslib-win32.c
> > index 7eedbe5859a..31030463cc9 100644
> > --- a/util/oslib-win32.c
> > +++ b/util/oslib-win32.c
> > @@ -828,3 +828,9 @@ char *qemu_get_host_name(Error **errp)
> >
> >     return g_utf16_to_utf8(tmp, size, NULL, NULL, NULL);
> > }
> > +
> > +size_t qemu_get_host_physmem(void)
> > +{
> > +    /* currently unimplemented */
> > +    return 0;
> > +}
>
> For Windows this may help:
>
> https://stackoverflow.com/questions/5553665/get-ram-system-size
>
> not sure about other OSes.
>
> Regards,
> BALATON Zoltan



-- 
Christian Ehrhardt
Staff Engineer, Ubuntu Server
Canonical Ltd

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