Using Xen's hypercall interface?

[Rig Gel]

Hi all,

- I'm sorry if this is a repost, I was informed that this is the correct
mailing list only after sending a msg to xen-users -

I would like to compile a simple ELF which would make a simple a hypercall
from a guest in order to
learn a bit more about the Xen Hypercall interface.
I tried including the hypervisor.h and -I'ing the ./extras/mini-os/ dir but
it seems that I'm missing a few flags or paths in order ot make it fully
compile correctly

Can anyone hint or explain a bit what is the appropriate way to link
against Xen's header files ?
I only need hypervisor.h in order to call some hypercalls

Attached below a sample of my code -

#include <hypervisor.h>

...
snip
...

void test_xen_version(int vers) {
HYPERVISOR_xen_version(vers);
}

( using the xe_version hypercall is just a mere example, I would like to
just know how to link/compile correctly against the required header
files/libs )

[Andrew Cooper]

Post by Rig Gel
Hi all,
- I'm sorry if this is a repost, I was informed that this is the
correct mailing list only after sending a msg to xen-users -
I would like to compile a simple ELF which would make a simple a
hypercall from a guest in order to
learn a bit more about the Xen Hypercall interface.
I tried including the hypervisor.h and -I'ing the ./extras/mini-os/
dir but it seems that I'm missing a few flags or paths in order ot
make it fully compile correctly
Can anyone hint or explain a bit what is the appropriate way to link
against Xen's header files ?
I only need hypervisor.h in order to call some hypercalls
Attached below a sample of my code -
#include <hypervisor.h>
...
snip
...
void test_xen_version(int vers) {
HYPERVISOR_xen_version(vers);
}
( using the xe_version hypercall is just a mere example, I would like
to just know how to link/compile correctly against the required header
files/libs )

It is not possible to make hypercalls from userspace directly. Allowing
such would cause all kinds of security problems. Linux and other
operating systems a kernel driver which allow hypercalls via ioctl()s on
/dev/xen/privcmd.

You are best starting with libxenctrl which is a thin userspace library
including OS abstraction to make hypercalls.
#include <stdio.h>
#include <xenctrl.h>

int main(void)
{
xc_interface *xch = xc_interface_open(NULL, NULL, 0);
int ver = xc_version(xch, XENVER_version, NULL);

printf("Xen version %d.%d\n", ver >> 16, ver & 0xffff);
xc_interface_close(xch);
return 0;
}

and compiled with `gcc foo.c -o foo -I/path/to/xenctrl.h
-L/path/to/libxenctrl.so -lxenctrl`

ought to get you started.

~Andrew

[Rig Gel]

Hi
/proc/xen/privcmd seem to exist only from dom0,
is there any extension or ko i should load in order to find it on other
kernels ?

Post by Rig Gel
Hi all,
- I'm sorry if this is a repost, I was informed that this is the
correct mailing list only after sending a msg to xen-users -
I would like to compile a simple ELF which would make a simple a
hypercall from a guest in order to
learn a bit more about the Xen Hypercall interface.
I tried including the hypervisor.h and -I'ing the ./extras/mini-os/ dir
but it seems that I'm missing a few flags or paths in order ot make it
fully compile correctly
Can anyone hint or explain a bit what is the appropriate way to link
against Xen's header files ?
I only need hypervisor.h in order to call some hypercalls
Attached below a sample of my code -
#include <hypervisor.h>
...
snip
...
void test_xen_version(int vers) {
HYPERVISOR_xen_version(vers);
}
( using the xe_version hypercall is just a mere example, I would like
to just know how to link/compile correctly against the required header
files/libs )
It is not possible to make hypercalls from userspace directly. Allowing
such would cause all kinds of security problems. Linux and other operating
systems a kernel driver which allow hypercalls via ioctl()s on
/dev/xen/privcmd.
You are best starting with libxenctrl which is a thin userspace library
including OS abstraction to make hypercalls.
#include <stdio.h>
#include <xenctrl.h>
int main(void)
{
xc_interface *xch = xc_interface_open(NULL, NULL, 0);
int ver = xc_version(xch, XENVER_version, NULL);
printf("Xen version %d.%d\n", ver >> 16, ver & 0xffff);
xc_interface_close(xch);
return 0;
}
and compiled with `gcc foo.c -o foo -I/path/to/xenctrl.h
-L/path/to/libxenctrl.so -lxenctrl`
ought to get you started.
~Andrew

[Ian Campbell]

On Mon, 2014-07-07 at 20:31 +0300, Rig Gel wrote:

Please avoid top posting and HTML emails on xen-devel.

/proc/xen/privcmd seem to exist only from dom0,
is there any extension or ko i should load in order to find it on other
kernels ?

If you mount xenfs on /proc/xen then privcmd should be usable from a
guest, although only up to the privilege of that guest.

Ian.