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

[BALATON Zoltan]

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.

> +    }
> +#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