Removing gaps in directory in a Ext2 File system

labandus · 11-01-2010, 08:36 AM

Directories(-entries) are in a EXT2 file system
managed in a singly linked list.
Delete files in the directory causes Gaps or holes to appear in
the linked list of the directory.How does a C-source code look like,
which would reorganize this list and remove the gaps or Holes.

thank you very much for your help.
labandus

neonsignal · 11-02-2010, 03:16 AM

Rather than operate on the raw directory (there used to be a libext2fs library, not sure what state it is in), you could simply do the following, in your choice of language:

1. create a temporary directory
2. move all the contents of the original directory to the temporary directory, eg using rename
3. remove the original directory
4. rename the temporary directory back to the original name

This would be more portable (ie, it would work on filesystems other than ext2), and less likely to lead to filesystem corruption if you get it wrong.

I cannot think of many reasons you would want to do this, because spaces left by deleted filename entries are reused anyway.

labandus · 11-02-2010, 04:15 PM

In fact , i am a newbie in kernel coding.
i got this theme from my university but i can code it....

if somebody can code out the solution In C, i'll read it understand it very well.

we should code in C with low-level IO, testing it on an extern devices (USB...).

This is the plan i had to test it:

1- Mounting of the Usb-device
2- copy a bunch of files on it
3- delete some files to create some Gaps or "holes".
4- show the directory (ies) withour holes.

5- unmount the device
6- with the code removing the gaps of the Linked list
7- mount it again.
8- display the directory without the gaps.

thank you to all the coders out there to theirs solutions

devnull10 · 11-02-2010, 04:18 PM

Sounds like a homework question to me. Sorry if not, but if so then don't expect much help.

labandus · 11-02-2010, 04:28 PM

thank you...

you know i am just beginning in this .... everyone has already needed help one time or another....

if you feel, you were just born talented ... then please free not the contribute... but if you remember your humble beginnings in this... you will surely remembered how much you needed help because you didn't know nothing about the theme, homework or not.

thank you again for your support...

labandus

devnull10 · 11-02-2010, 04:46 PM

There is no problem with asking for help but when people are giving up their time to offer that help it is nice if you at least make an attempt yourself first rather than asking for it on a plate. Perhaps try posting the code you have written so far and make your question more specific.

Anyway, I'll offer a little picture diagram that may help you :

Code:

NODE1 --> NODE2 --> NODE3 --> NODE4 --> NODE5

Let's say the definition of a node is as follows (simple example):

Code:

struct node {
  int value;
  struct node *next_node;
}

If you delete say NODE2 from the example then you need to change the next_node pointer of NODE2 to point to NODE4 rather than NODE3. So, when you are traversing the list to find the element to delete you either want to be looking one in front (so you can check whether the next element is the one you are interested in and then update the current element), or keep a pointer to the previous node (so if the current node is the one you are interested in, update the previous node with the pointer to the next node). Either method will work - you choose.

Your final list will then be:

Code:

NODE1 --> NODE2 --> NODE4 --> NODE5