Today, the openSUSE Weekly Newsletter team will have the translation sessions for the special edition created yesterday.

Join us from 12:00 UTC to 15:00 UTC in #opensuse-newsletter on freenode. (Schedule)

Los dias 17 al 21 de Junio del 2009 se llevara a cabo el Primer Congreso Centroamericano de Software Libre, en Nicaragua.

Mas informacion, haciendo click en la Ranita

Many of the maintainers of linux-kernel maintain a git repository. I usually have clones of various such repositories.

For example I have clones of
Linus Torvalds's repo:
git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git
Block Maintainer, Jens Axboe's repo:
git://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux-2.6-block.git
...

If I do individual clones of all these repositories, it downloads and maintains duplicate copies of same objects wasting disk space, and network bandwidth.
git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git
git clone git://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux-2.6-block.git

So I was looking for a way to share the common objects so that duplicate objects wont waste disk and network. And no surprise, git has a way to do that. Just that I was unaware of a simple option, "--reference".
git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git
git clone --reference linux-2.6/ git://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux-2.6-block.git

---

Difference between cloning Jens' git with and without --reference to Linus's git.

# git clone git://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux-2.6-block.git
Initialized empty Git repository in /home/knikanth/labs-sw/linus/linux-2.6-block/.git/
remote: Counting objects: 1180249, done.
remote: Compressing objects: 100% (295444/295444), done.
remote: Total 1180249 (delta 984716), reused 1073684 (delta 878311)
Receiving objects: 100% (1180249/1180249), 289.32 MiB | 496 KiB/s, done.
Resolving deltas: 100% (984716/984716), done.
Checking out files: 100% (27842/27842), done.
# du -sh linux-2.6-block/
714M linux-2.6-block/


# git clone --reference linux-2.6/ git://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux-2.6-block.git
Initialized empty Git repository in /home/knikanth/labs-sw/linus/linux-2.6-block/.git/
remote: Counting objects: 111061, done.
remote: Compressing objects: 100% (19021/19021), done.
remote: Total 100463 (delta 84138), reused 95679 (delta 79959)
Receiving objects: 100% (100463/100463), 23.21 MiB | 1209 KiB/s, done.
Resolving deltas: 100% (84138/84138), completed with 8189 local objects.
Checking out files: 100% (27842/27842), done.
# du -sh linux-2.6-block/
468M linux-2.6-block/

---

--reference automatically sets up .git/objects/info/alternates to obtain objects from the reference repository. Now I wonder whether it is possible to have circular references, multiple references, etc.. The plural file name, "alternates" suggests it should be possible, but "git clone" ignores multiple --reference on the command line!

BTW git uses SHA-1 digests to identify objects. I wonder what is the chance of a SHA-1 collision and how git handles it? The SHA-1 digest has 40 Hex-digits == 160 bits.. So at most, only 2¹⁶⁰ objects are possible. :-)

img1 = new ImageIcon(getClass().getResource(“/Imagenes/1.jpg”)).getImage();

After a long time, with lots of not visible activity Kolab, the groupware server build with many known open source components, is slowly getting back into openSUSE. For a year or so it was not possible to use Kolab on openSUSE versions newer than 10.3. That was due to the move from openldap 2.3 to 2.4. The latter does no longer support slurpd as replication mechanism, but uses syncrepl instead. Hence, kolab had to be extended to be able to work with new replication protocol. After that the way the webclient horde was packaged, changed from (to make a long story short) 1 big package, to many small packages. This in preparation for horde4. Today, the following message was posted to the kolab-user e-maillist:

after a lot of tests on a virtual system I finally upgraded my
productive Kolab server to 2.2.1 with the Suse packages.

Now you should now, that kolab-2.2.1 was released about month in April 2009. Although we (Marcus Huewe, Alar Sing, and the author of this article) are not there yet, seeing this message means a lot to us. We’re making good process!

Хотел бы напомнить, что презентации по темам, связанным с языками С и С++ и не только, доступны на ресурсе:
SlideShare

Рассмотрим работу с одно связанным списком, но предположим, что в списке каждая предыдущая структура хранит указатель на последующую. В этом случае, как я упоминал ранее в предыдущем посте, надо хранить указатель на первую структуру в списке. Если мы потеряем первую структуру, то потеряем и элементы списка. А почему? Она - одно связанная, указатель - с предыдущей на последующую, а, следовательно, мы можем двигаться только от первой к последней структуре в списке. Иначе не получится! ;)
А теперь код. Он похож на предыдущей, только вместо pLast и prev используем pFirst и next:

typedef struct S2{int a; int b; S2* next;} S2_t;

 // одно связанный список

 S2_t *p2=0, *pLast2=0, *pFirst=0;

 //построение списка

 for(int i=0;i<10;++i)
 {
  p2=(S2_t *)malloc(sizeof(S2_t));
  memset(p2,0,sizeof(S2_t));
  p2->a=i;
  p2->b=i+10;
  if(pLast2)
   pLast2->next=p2;
  else
   pFirst=p2;
  pLast2=p2;
 }

 //работа со списком

 p2=pFirst;
 while(p2){
  printf("a: %d b: %d\n", p2->a,p2->b);
  p2=p2->next;
 }

 //Удаляем четные элементы

 p2=pFirst;
 S2_t* p22=pFirst;
 while(p2){
  if(!(p2->a&1)){
   if(p2==pFirst){
    p22=p2->next;
    pFirst=p22;
    free(p2);
    p2=p22;
   }else{
    p22->next=p2->next;
    free(p2);
    p2=p22->next;
   }
  }else{
   p22=p2;
   p2=p2->next;
  }
 }

 printf("After removing:\n");
 p2=pFirst;
 while(p2){
  printf("a: %d b: %d\n", p2->a,p2->b);
  p2=p2->next;
 }

 //удаление списка

 p2=pFirst;
 while(p2){
  pFirst=p2->next;
  free(p2);
  p2=pFirst;
 }

Посмотрим как работают динамические списки. Из чего они состоят? Из структур, в каждой из которой есть указатель на предыдущую либо последующую. Это верно для одно связанных списков. У дву связанных есть указатель на предыдущую и последующую одновременно.
Структура может выглядеть так:

typedef struct S1{int a; int b; S1* prev;} S1_t; 

- имеет указатель на предыдущую

typedef struct S2{int a; int b; S2* next;} S2_t; 

- имеет указатель на последующую

Построим для первой структуры список из 10 элементов:

 printf("first:\n");
 // односвязанный список
 S1_t *p1=0, *pLast=0;
 //построение списка
 for(int i=0;i<10;++i)
 {
  p1=(S1_t *)malloc(sizeof(S1_t));
  memset(p1,0,sizeof(S1_t));
  p1->a=i;
  p1->b=i+10;
  if(pLast)
   p1->prev=pLast;
  pLast=p1;
 }

Выведем список на экран:

 
 p1=pLast;
 while(p1){
  printf("a: %d b: %d\n", p1->a,p1->b);
  p1=p1->prev;
 }

Удалим из списка структуры, которые содержат первое нулевое поле либо четное:

 
 p1=pLast;
 S1_t* p11=pLast;
 while(p1){
  if(!(p1->a&1)){
   if(p1==pLast){
    p11=p1->prev;
    pLast=p11;
    free(p1);
    p1=p11;
   }else{
    p11->prev=p1->prev;
    free(p1);
    p1=p11->prev;
   }
  }else{
   p11=p1;
   p1=p1->prev;
  }
 }

После работы надо освободить память:

 p1=pLast;
 while(p1){
  pLast=p1->prev;
  free(p1);
  p1=pLast;
 }

В начале работы со списком я всегда устанавливаю указатель p, с которым работаю, в начало списка.
При работе с одно связанным списком главное хранить указатель на последний элемент списка, если в списке указатели в структурах указывают с последующей на предыдущую структуры.
И надо хранить указатель на первую структуру в списке, если предыдущая структура хранит указатель на последующую.
В следующем посте я приведу пример для такой структуры.

Had 1.5 weeks of vacation to travel with 2 friends, a certain mouse, and various Fluffs to Denmark to visit a friend of theirs.

Friday (24th april): Roadtrip starting at 10:00 in Nuernberg ... We drove straight to Hamburg as the first days stop. Spent the evening at the Aussenalster, lounging at a jetty cafe and enjoying the setting sun over the water. Tried not to get run over by Joggers and Bikers. Hotel was a nice one in St Georg, except I could listen to everything happen in the neighbouring rooms and the staircase.

Saturday: Walked around the Binnenalster and the City. Met by chance my brother who lives in Hamburg. Met an old study friend of Edith and spent more time walking around and looking at St Pauli / Landungsbruecken, Ferries, Oevelgoenne and Blankenese. Then we drove on towards Luebeck. Luebeck was quieter and emptier then we imagined (or we did not really find the cool places). So Steakhouse first, and Irish Pub across the nice Hotel (Alter Speicher) later on.

Sunday: Visited the Guenter Grass House and the Figurenmuseum (funny enough, lots of hand puppets from all over the world ... but no Muppets (r).) ... Then drove on towards Denmark, where we spent the night in the even quieter costal town Fredericia.

Denmark smelled strongly of Guelle everywhere, farmers have been busy getting it to the fields apparently.

Monday: Drove on to visit Lindholm Hoje, a Viking grave site and after walking around it a bit, drove on the Ålbæk, near the northern most tip of Denmark. We had rented a vacation flat for 4 nights at a farmers place, quiet and nice. Lots of drinking and chatting.

Tuesday: Visited Skagen withs its art museum, and the tip of denmark in Grenen, where Skagerrak (Nordsee aka North Sea) and Kattegat (Ostsee aka Baltic Sea) meet each other, and the
a large aquarium in Hirthals.

Wednesday: A walk through the woods.

Thursday: More sightseeing around the area, visited to only left-as-is wandering dune Råbjerg Mile, various beaches on both the North and Baltic Sea. Enjoyed local fish in the evening.

Friday: Drove (mostly with a Ferry from Fredrikshaven) to Goeteborg. Spent the afternoon walking around in Goeteborg, drinking beer and watching the local girls who obviously are accustomed to walk around in shorts and tshirts at 10 degree celsius. Nice hotel called Vasa.

Saturday: Drove through south sweden and denmark to Gedser and then ferried over to Rostock. Found a nice hotel in Warnemuende and relaxed with beach walking and beer/wine.

Sunday: More refreshing beach walking, saying good by to the sea... Drove southwards, with a lunch stop in Potsdam to visit Sanssouci, then onwards back to Nuernberg.

Monday-Wednesday: Washing, helping Rasmus with his home network and getting barbeque as thanks, fixing libgphoto2...

Images are here.