On 26/09/16 13:59, Harini V Reddy wrote:
> Hi,
>
> I am Harini, an undergraduate pursuing Bachelors Of Engineering
> in Information Science having some prior experience with coding
> in C and Golang.
>
> I am interested in applying for Outreachy Round 13 in golang bindings
> for libxl project.
>
> Can I know the first contributions to be made for the same?
>
> I would really appreciate it if you could give some insights in this regard
Harini,
Thanks for your interest in the Xen Project!
First, I want to emphasize that Outreachy internships should be
considered a full-time job. As part of the application process you
will be asked to confirm that you will not be taking any classes, nor
have any other significant commitments (such as another job) during
the period of the internship.
Now on to the bite-sized task. We've actually found that one of the
difficult parts of getting going with our project is making sure that
you understand how to get your whole system and environment set up.
And another thing we want to see is to what degree you can balance
figuring things out, finding the answers on the web, and asking for
help when you need it.
So with that in mind, we've started experimenting with tasks which
don't contribute very much to the project directly, but provide a
really solid base of knowledge to do further contributions.
So here's my challenge for you.
-------
OUTCOME
Attached is the very beginnings of a set of golang bindings that I
wrote for a project of my own. They contain an implementation of
Context.Open() and Context.ListCpupool(), along with a structure
called Bitmap. Bitmap is used to store an array of bits in eight-bit
chunks. So bits 0-7 are bits 0-7 of Bitmap.bitmap[0]; bits 8-15 are
bits 0-7 of Bitmap.bitmap[1], and so on.
On this structure, there are three "stub" methods defined -- Test(),
Set(), and Clear(). (These have labeled with comments which contain
"TODO".) Please implement these methods, so that the main() function
at the bottom of the file runs properly.
You can refer to the C versions of these functions in
xen.git/tools/libxl/libxl_utils.c. The function names are
libxl_bitmap_test(), libxl_bitmap_set(), and libxl_bitmap_reset().
("reset" in this case is the same as "Clear" in the methods I've
defined.)
Please post a copy of your .go program with these functions implemented,
along with the results of output, to xen-devel.
STEPS
1. Set up a system running Linux
If you don't have one, Ubuntu, Fedora, or Debian should all be fine.
2. Download, build, and install the latest development
version of Xen. The following page should be useful:
https://wiki.xenproject.org/wiki/Compiling_Xen_From_Source
I would recommend using "make debball" or "make rpmball" over the
"make install".
3. You'll need to build an image for at least one guest VM.
There are tons of options here, but one really simple thing would be
to follow this HOWTO from a previous OPW intern:
https://umasharma17.wordpress.com/2015/02/13/creating-guests-using-xl-in-xen/
4. Implement the stub methods for Bitmap.
The go program will need to Open() the context, then call DomainInfo()
on the target domain ID, and output the required info based on "xl
list".
libxl.go uses cgo to compile a library against C. If you have the
libraries set up properly, the current version should just work.
------
That's it! Remember that the goal of this is to see how well you
balance figuring things out on your own vs asking questions. So try
to figure things out on your own, but when you run into a bit of
difficultly, don't hesitate to ask questions or clarification --
particularly at the beginning.
You can ask questions either here on xen-devel or on the #xendevel or
#xen-opw channels on freenode IRC.
Good luck, and look forward to hearing from you!
-George
/*
* Copyright (C) 2016 George W. Dunlap, Citrix Systems UK Ltd
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License as
* published by the Free Software Foundation; version 2 of the
* License only.
*
* This program is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
* 02110-1301, USA.
*/
package main
/*
#cgo LDFLAGS: -lxenlight -lyajl
#include <stdlib.h>
#include <libxl.h>
*/
import "C"
import (
"unsafe"
"fmt"
"time"
)
type Context struct {
ctx *C.libxl_ctx
}
var Ctx Context
func (Ctx *Context) IsOpen() bool {
return Ctx.ctx != nil
}
func (Ctx *Context) Open() (err error) {
if Ctx.ctx != nil {
return
}
ret := C.libxl_ctx_alloc(unsafe.Pointer(&Ctx.ctx), C.LIBXL_VERSION, 0, nil)
if ret != 0 {
err = fmt.Errorf("Allocating libxl context: %d", ret)
}
return
}
func (Ctx *Context) Close() (err error) {
ret := C.libxl_ctx_free(unsafe.Pointer(Ctx.ctx))
Ctx.ctx = nil
if ret != 0 {
err = fmt.Errorf("Freeing libxl context: %d", ret)
}
return
}
// Builtins
type Domid uint32
type MemKB uint64
// FIXME: Use the idl to generate types
type Dominfo struct {
// FIXME: uuid
Domid Domid
Running bool
Blocked bool
Paused bool
Shutdown bool
Dying bool
Never_stop bool
Shutdown_reason int32 // FIXME shutdown_reason enumeration
Outstanding_memkb MemKB
Current_memkb MemKB
Shared_memkb MemKB
Paged_memkb MemKB
Max_memkb MemKB
Cpu_time time.Duration
Vcpu_max_id uint32
Vcpu_online uint32
Cpupool uint32
Domain_type int32 //FIXME libxl_domain_type enumeration
}
func (Ctx *Context) DomainInfo(Id Domid) (di *Dominfo, err error) {
if Ctx.ctx == nil {
err = fmt.Errorf("Context not opened")
return
}
var cdi C.libxl_dominfo
ret := C.libxl_domain_info(Ctx.ctx, unsafe.Pointer(&cdi), C.uint32_t(Id))
// FIXME: IsDomainNotPresentError
if ret != 0 {
err = fmt.Errorf("libxl_domain_info failed: %d", ret)
return
}
// FIXME -- use introspection to make this more robust
di = &Dominfo{}
di.Domid = Domid(cdi.domid)
di.Running = bool(cdi.running)
di.Blocked = bool(cdi.blocked)
di.Paused = bool(cdi.paused)
di.Shutdown = bool(cdi.shutdown)
di.Dying = bool(cdi.dying)
di.Never_stop = bool(cdi.never_stop)
di.Shutdown_reason = int32(cdi.shutdown_reason)
di.Outstanding_memkb = MemKB(cdi.outstanding_memkb)
di.Current_memkb = MemKB(cdi.current_memkb)
di.Shared_memkb = MemKB(cdi.shared_memkb)
di.Paged_memkb = MemKB(cdi.paged_memkb)
di.Max_memkb = MemKB(cdi.max_memkb)
di.Cpu_time = time.Duration(cdi.cpu_time)
di.Vcpu_max_id = uint32(cdi.vcpu_max_id)
di.Vcpu_online = uint32(cdi.vcpu_online)
di.Cpupool = uint32(cdi.cpupool)
di.Domain_type = int32(cdi.domain_type)
return
}
func (Ctx *Context) DomainUnpause(Id Domid) (err error) {
if Ctx.ctx == nil {
err = fmt.Errorf("Context not opened")
return
}
ret := C.libxl_domain_unpause(Ctx.ctx, C.uint32_t(Id))
if ret != 0 {
err = fmt.Errorf("libxl_domain_unpause failed: %d", ret)
}
return
}
// typedef struct {
// uint32_t size; /* number of bytes in map */
// uint8_t *map;
// } libxl_bitmap;
// Rather than trying to re-implement bitmap types in go and translate
// them, we implement the Go bitmap type such that the underlying data
// can easily be handed to the libxl bitmap types; but we make it a Go
// construct so that we can
type Bitmap struct {
bitmap []C.uint8_t
}
func (bm *Bitmap) Alloc(max int) {
bm.bitmap = make([]C.uint8_t, (max + 7) / 8)
}
// Return a Go bitmap which is a copy of the referred C bitmap.
func bitmapCToGo(cbm *C.libxl_bitmap) (bm Bitmap) {
// Alloc a Go slice for the bytes
size := int(cbm.size)
bm.Alloc(size*8)
// Make a slice pointing to the C array
mapslice := (*[1 << 30]C.uint8_t)(unsafe.Pointer(cbm._map))[:size:size]
// And copy the C array into the Go array
copy(bm.bitmap, mapslice)
return
}
func (bm *Bitmap) Max() (int) {
return len(bm.bitmap) * 8
}
func (bm *Bitmap) Test(bit int) (bool) {
// TODO: Implement
return false
}
// FIXME: Do we really just want to silently fail here?
func (bm *Bitmap) Set(bit int) {
// TODO: Implement
}
func (bm *Bitmap) Clear(bit int) {
// TODO: Implement
}
// # Consistent with values defined in domctl.h
// # Except unknown which we have made up
// libxl_scheduler = Enumeration("scheduler", [
// (0, "unknown"),
// (4, "sedf"),
// (5, "credit"),
// (6, "credit2"),
// (7, "arinc653"),
// (8, "rtds"),
// ])
type Scheduler int
var (
SchedulerUnknown Scheduler = 0
SchedulerSedf Scheduler = 4
SchedulerCredit Scheduler = 5
SchedulerCredit2 Scheduler = 6
SchedulerArinc653 Scheduler = 7
SchedulerRTDS Scheduler = 8
)
// const char *libxl_scheduler_to_string(libxl_scheduler p);
// int libxl_scheduler_from_string(const char *s, libxl_scheduler *e);
func (s Scheduler) String() (string) {
cs := C.libxl_scheduler_to_string(C.libxl_scheduler(s))
// No need to free const return value
return C.GoString(cs)
}
func SchedulerFromString(name string) (s Scheduler, err error) {
cname := C.CString(name)
defer C.free(unsafe.Pointer(cname))
var cs C.libxl_scheduler
ret := C.libxl_scheduler_from_string(cname, &cs)
if ret != 0 {
err = fmt.Errorf("libxl_scheduler_from_string failed: %d", ret)
return
}
s = Scheduler(cs)
return
}
// libxl_cpupoolinfo = Struct("cpupoolinfo", [
// ("poolid", uint32),
// ("pool_name", string),
// ("sched", libxl_scheduler),
// ("n_dom", uint32),
// ("cpumap", libxl_bitmap)
// ], dir=DIR_OUT)
type CpupoolInfo struct {
PoolId uint32
PoolName string
Scheduler Scheduler
DomainCount int
CpuMap Bitmap
}
// libxl_cpupoolinfo * libxl_list_cpupool(libxl_ctx*, int *nb_pool_out);
// void libxl_cpupoolinfo_list_free(libxl_cpupoolinfo *list, int nb_pool);
func (Ctx *Context) ListCpupool() (list []CpupoolInfo) {
var nbPool C.int
c_cpupool_list := C.libxl_list_cpupool(Ctx.ctx, &nbPool)
defer C.libxl_cpupoolinfo_list_free(c_cpupool_list, nbPool)
if int(nbPool) == 0 {
return
}
// Magic
cpupoolListSlice := (*[1 << 30]C.libxl_cpupoolinfo)(unsafe.Pointer(c_cpupool_list))[:nbPool:nbPool]
for i := range cpupoolListSlice {
var info CpupoolInfo
info.PoolId = uint32(cpupoolListSlice[i].poolid)
info.PoolName = C.GoString(cpupoolListSlice[i].pool_name)
info.Scheduler = Scheduler(cpupoolListSlice[i].sched)
info.DomainCount = int(cpupoolListSlice[i].n_dom)
info.CpuMap = bitmapCToGo(&cpupoolListSlice[i].cpumap)
list = append(list, info)
}
return
}
func (Ctx *Context) CpupoolFindByName(name string) (info CpupoolInfo, found bool) {
plist := Ctx.ListCpupool()
for i := range plist {
if plist[i].PoolName == name {
found = true
info = plist[i]
return
}
}
return
}
// int libxl_cpupool_create(libxl_ctx *ctx, const char *name,
// libxl_scheduler sched,
// libxl_bitmap cpumap, libxl_uuid *uuid,
// uint32_t *poolid);
// int libxl_cpupool_destroy(libxl_ctx *ctx, uint32_t poolid);
// int libxl_cpupool_rename(libxl_ctx *ctx, const char *name, uint32_t poolid);
// int libxl_cpupool_cpuadd(libxl_ctx *ctx, uint32_t poolid, int cpu);
// int libxl_cpupool_cpuadd_node(libxl_ctx *ctx, uint32_t poolid, int node, int *cpus);
// int libxl_cpupool_cpuadd_cpumap(libxl_ctx *ctx, uint32_t poolid,
// const libxl_bitmap *cpumap);
// int libxl_cpupool_cpuremove(libxl_ctx *ctx, uint32_t poolid, int cpu);
// int libxl_cpupool_cpuremove_node(libxl_ctx *ctx, uint32_t poolid, int node, int *cpus);
// int libxl_cpupool_cpuremove_cpumap(libxl_ctx *ctx, uint32_t poolid,
// const libxl_bitmap *cpumap);
// int libxl_cpupool_movedomain(libxl_ctx *ctx, uint32_t poolid, uint32_t domid);
// int libxl_cpupool_info(libxl_ctx *ctx, libxl_cpupoolinfo *info, uint32_t poolid);
func main() {
var Ctx Context
err := Ctx.Open()
if err != nil {
fmt.Printf("Opening context: %v\n", err)
return
}
pools := Ctx.ListCpupool()
if len(pools) > 1 {
pool := pools[0]
fmt.Printf("%v\n", pool)
pool.CpuMap.Clear(1)
pool.CpuMap.Set(1)
pool.CpuMap.Set(2)
pool.CpuMap.Clear(2)
fmt.Printf("cpumap: ")
for i := 0; i < pool.CpuMap.Max() ; i++ {
if pool.CpuMap.Test(i) {
fmt.Printf("x")
} else {
fmt.Printf("-")
}
}
fmt.Printf("\n")
} else {
fmt.Printf("No pools returned!")
}
Ctx.Close()
}
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