Xen devel - Jun 2012 - Regarding domctl hypercall from dom0 kernel...

Hi,

I am trying to invoke domctl hypercall (XEN_DOMCTL_SCHEDOP_putinfo) from dom0
kernel. For my research i need to dynamically change the credits for guest
domains. Following are my code additions,

Kernel modifications: 
In /source/arch/x86/include/asm/xen/hypercall.h added

static inline int
HYPERVISOR_domctl(unsigned long arg)
{
        return _hypercall1(int, domctl, arg);
}


In source/include/xen/interface/xen.h added 

#define __HYPERVISOR_domctl               36


added a system call to invoke hypercall from dom0 user space, system call code
is as follows

#include <linux/linkage.h>
#include <linux/kernel.h>
#include <asm/xen/hypervisor.h>
#include <asm/xen/hypercall.h>

#ifndef uint64_aligned_t
#define uint64_aligned_t uint64_t
#endif

#define XEN_DOMCTL_INTERFACE_VERSION 0x00000007

/* XEN_DOMCTL_scheduler_op */
/* Scheduler types. */
#define XEN_SCHEDULER_SEDF     4
#define XEN_SCHEDULER_CREDIT   5
#define XEN_SCHEDULER_CREDIT2  6
#define XEN_SCHEDULER_ARINC653 7

/* Set or get info? */
#define XEN_DOMCTL_SCHEDOP_putinfo 0
#define XEN_DOMCTL_SCHEDOP_getinfo 1
struct xen_domctl_scheduler_op {
    uint32_t sched_id;  /* XEN_SCHEDULER_* */
    uint32_t cmd;       /* XEN_DOMCTL_SCHEDOP_* */
    union {
        struct xen_domctl_sched_sedf {
            uint64_aligned_t period;
            uint64_aligned_t slice;
            uint64_aligned_t latency;
            uint32_t extratime;
            uint32_t weight;
        } sedf;
        struct xen_domctl_sched_credit {
            uint16_t weight;
            uint16_t cap;
        } credit;
        struct xen_domctl_sched_credit2 {
            uint16_t weight;
        } credit2;
    } u;
};
typedef struct xen_domctl_scheduler_op xen_domctl_scheduler_op_t;


struct xen_domctl_synced {
    char is_synchronized;
    int sync_done;
    char sync_currently_running;
};
typedef struct xen_domctl_synced xen_domctl_synced_t;

 struct xen_domctl {
        uint32_t cmd;
        #define XEN_DOMCTL_scheduler_op                  16
        #define XEN_DOMCTL_set_synced                    68
        #define XEN_DOMCTL_get_synced                    69
        uint32_t interface_version; /* XEN_DOMCTL_INTERFACE_VERSION */
        domid_t  domain;
        union {
                struct xen_domctl_scheduler_op      scheduler_op;
                struct xen_domctl_synced            synced;

                uint8_t                             pad[128];
        } u;
};
typedef struct xen_domctl xen_domctl_t;

asmlinkage long sys_mycall(int i)
{
        int retval;
        xen_domctl_t dom;

        dom.domain = i;
        dom.interface_version = XEN_DOMCTL_INTERFACE_VERSION;
        dom.cmd = XEN_DOMCTL_scheduler_op;
        dom.u.scheduler_op.sched_id = XEN_SCHEDULER_CREDIT;
        dom.u.scheduler_op.cmd = XEN_DOMCTL_SCHEDOP_putinfo;
        dom.u.scheduler_op.u.credit.weight=128;
        dom.u.scheduler_op.u.credit.cap = 1;
  
        retval = HYPERVISOR_domctl((unsigned long)&dom);
        printk(KERN_DEBUG "XEN_DOMCTL_SCHEDOP_putinfo hypercall returned
%d\n", retval);

        return retval;
}



Hypercall returns a -22 (EINVAL) error code.

Any help would be appreciated.

Thanks

On Thu, 2012-06-21 at 22:09 +0100, Tapdiya, Ashish
wrote:
> added a system call to invoke hypercall from dom0 user space, system
> call code is as follows
Why not just make the hypercall from userspace (via libxenctrl)
directly? All the necessary infrastructure is in place and is known to
work because the toolstack uses it extensively.

domctls are not really supposed to be used from the kernel since they
are not stable across Xen releases.

Ian.