[ Help! ] how is ctx->xch in xen/tools/libxl/xl_cmdimpl.c initialized?

[ Help! ] how is ctx->xch in xen/tools/libxl/xl_cmdimpl.c initialized?

[Li Yechen]

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I try to trap the xl command: main_memset() in tools/libxl/xl.h
and it goes to do_xen_hypercall(xch, *hypercall) on line 246,
xen4.1.2/tools/libxc/xc_private.c

this function then call: xch->ops->u.privcmd.hypercall() which is a
function pointer
the xch is a member of global varible: libxl_ctx *ctx, which is in line66，
tools/libxl/xl_cmdimpl.c

then I can't find where the function pointer goes to, nor does the place
where this function pointer is initialized.
Any one is familiar with this variable? Help me please! Thank you very much!

-- 
Yechen Li

Team of System Virtualization and Cloud Computing
School of Electronic Engineering  and Computer Science,
Peking University, China

Nothing is impossible because impossible itself  says: " I'm possible "
lccycc From PKU

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Re: [ Help! ] how is ctx->xch in xen/tools/libxl/xl_cmdimpl.c initialized?

[Wei Liu]

On Thu, Apr 11, 2013 at 02:06:58PM +0100, Li Yechen wrote:
> I try to trap the xl command: main_memset() in tools/libxl/xl.h
> and it goes to do_xen_hypercall(xch, *hypercall) on line 246, xen4.1.2/tools/libxc/xc_private.c
> 
> this function then call: xch->ops->u.privcmd.hypercall() which is a function pointer
> the xch is a member of global varible: libxl_ctx *ctx, which is in line66， tools/libxl/xl_cmdimpl.c
> 
> then I can't find where the function pointer goes to, nor does the place where this function pointer is initialized.
> Any one is familiar with this variable? Help me please! Thank you very much!
> 

xch is a handle to Xen privcmd. Please look at OS dependent code in
libxc such as xc_linux_osdep.c


Wei.

> --
> Yechen Li
> 
> Team of System Virtualization and Cloud Computing
> School of Electronic Engineering  and Computer Science,
> Peking University, China
> 
> Nothing is impossible because impossible itself  says: " I'm possible "
> lccycc From PKU

> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xen.org
> http://lists.xen.org/xen-devel


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Re: [ Help! ] how is ctx->xch in xen/tools/libxl/xl_cmdimpl.c initialized?

[Li Yechen]

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Thank you very much!
I find the function pointer point to :
.u.privcmd.hypercall = &linux_privcmd_hypercall      on Line 423

but this function:linux_privcmd_hypercall() in xen4.2.1/tools/libxc/xc_linux
_osdep.c, Line 113
goes to a python script:
xen4.2.1/tools/python/xen/util/SSHTransport.py, Line 26
then it seems to call a function name lwip_ioctl:
> return lwip_ioctl(files[fd],socket.fd, FIONBIO, &nblock);
this function does not belong to xen

I just want to find out how xl comnand works, does it actually call this
function?
The code of Xen of this part have no any commons..It's too hard to
understand.
Help me please Orz


On Fri, Apr 12, 2013 at 2:41 AM, Wei Liu <wei.liu2@citrix.com> wrote:

> On Thu, Apr 11, 2013 at 02:06:58PM +0100, Li Yechen wrote:
> > I try to trap the xl command: main_memset() in tools/libxl/xl.h
> > and it goes to do_xen_hypercall(xch, *hypercall) on line 246,
> xen4.1.2/tools/libxc/xc_private.c
> >
> > this function then call: xch->ops->u.privcmd.hypercall() which is a
> function pointer
> > the xch is a member of global varible: libxl_ctx *ctx, which is in
> line66， tools/libxl/xl_cmdimpl.c
> >
> > then I can't find where the function pointer goes to, nor does the place
> where this function pointer is initialized.
> > Any one is familiar with this variable? Help me please! Thank you very
> much!
> >
>
> xch is a handle to Xen privcmd. Please look at OS dependent code in
> libxc such as xc_linux_osdep.c
>
>
> Wei.
>
> > --
> > Yechen Li
> >
> > Team of System Virtualization and Cloud Computing
> > School of Electronic Engineering  and Computer Science,
> > Peking University, China
> >
> > Nothing is impossible because impossible itself  says: " I'm possible "
> > lccycc From PKU
>
> > _______________________________________________
> > Xen-devel mailing list
> > Xen-devel@lists.xen.org
> > http://lists.xen.org/xen-devel
>
>


-- 
Yechen Li

Team of System Virtualization and Cloud Computing
School of Electronic Engineering  and Computer Science,
Peking University, China

Nothing is impossible because impossible itself  says: " I'm possible "
lccycc From PKU

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Re: [ Help! ] how is ctx->xch in xen/tools/libxl/xl_cmdimpl.c initialized?

[Wei Liu]

Please don't top-post.

On Tue, Apr 16, 2013 at 04:17:46PM +0100, Li Yechen wrote:
> Thank you very much!
> I find the function pointer point to :
> .u.privcmd.hypercall = &linux_privcmd_hypercall      on Line 423
> 
> but this function:linux_privcmd_hypercall() in xen4.2.1/tools/libxc/xc_linux_osdep.c, Line 113
> goes to a python script:
> xen4.2.1/tools/python/xen/util/SSHTransport.py, Line 26
> then it seems to call a function name lwip_ioctl:
> > return lwip_ioctl(files[fd],socket.fd, FIONBIO, &nblock);
> this function does not belong to xen
> 

It looks like your indexing utility screwed you. That's not a funciton,
is a structure defined in the same file. That structure contains a bunch
of function pointers.


Wei.

> I just want to find out how xl comnand works, does it actually call this function?
> The code of Xen of this part have no any commons..It's too hard to understand.
> Help me please Orz
> 
> 

Re: [ Help! ] how is ctx->xch in xen/tools/libxl/xl_cmdimpl.c initialized?

[Dario Faggioli]

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On mar, 2013-04-16 at 23:17 +0800, Li Yechen wrote:
> Thank you very much!
> I find the function pointer point to :
> .u.privcmd.hypercall = &linux_privcmd_hypercall      on Line 423
> 
> [snip]
> 
> I just want to find out how xl comnand works, does it actually call
> this function?
> The code of Xen of this part have no any commons..It's too hard to
> understand.
>
Ok (first, sorry for the delay), you said you're interested in what
main_memset(), in xl_cmdimpl.c, end up doing at the hypervisor level,
right?

Up to what I can see, the call chain is this:
 main_memset() [tools/libxl/xl_cmdimpl.c]
  |
  --> set_memory_target() [tools/libxl/xl_cmdimpl.c]
       |
       --> xc_domain_setmaxmem() ? xc_domain_set_pod_target() [tools/libxl/libxl.c]
            |
            --> xc_domain_setmaxmem() [tools/libxc/xc_domain.c]:
                 domctl.cmd = XEN_DOMCTL_max_mem;
                 domctl.u.max_mem.max_memkb = max_memkb;
                 return do_domctl(xch, &domctl);

So, here is when the hypercall is invoked (Assuming that you're
interested in the path that calls xc_domain_setmaxmem, otherwise, the
hypercall invoked within xc_domain_set_pod_target() is
XENMEM_set_pod_target).

Now, when looking for XEN_DOMCTL_max_mem, consider the reference to it
that can be found in xen/common/domctl.c at (around) line 886:

    case XEN_DOMCTL_max_mem:
    {
        unsigned long new_max;

        ret = -EINVAL;
        new_max = op->u.max_mem.max_memkb >> (PAGE_SHIFT-10);

        spin_lock(&d->page_alloc_lock);
        /*
         * NB. We removed a check that new_max >= current tot_pages; this means
         * that the domain will now be allowed to "ratchet" down to new_max. In
         * the meantime, while tot > max, all new allocations are disallowed.
         */
        d->max_pages = new_max;
        ret = 0;
        spin_unlock(&d->page_alloc_lock);
    }
    break;

And this is it. As Wei was telling you, how the hypercall is actually
issued is what the OS dependent code does with all those functions
pointer you found. OTOH, when you're interested in knowing _what_ an
hypercall actually does, I'd dare to recommend digging until you find
the hypercall name (in this case XEN_DOMCTL_max_mem) and then
grep-ing/cscope-ing it directly in the hypervisor code.

Does that help? :-)

Regards,
Dario

-- 
<<This happens because I choose it to happen!>> (Raistlin Majere)
-----------------------------------------------------------------
Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)


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