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Ghost Cat



Joined: 03 Nov 2004
Posts: 16
Ghost Cat
I have a question about the file system? Is it possible to create a file
system in which each block "knows" the location of the previous block? This
way the FAT can be slimmed down because only the location of the last block
of each file should be cataloged and the files can be read from the end to
the beginning, each block directing the hard drive where to look for the
next one.

So the recording is done from the beginning to the end of the file and the
reading is done in opposite direction.
Post 03 Nov 2004, 20:33
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crc



Joined: 21 Jun 2003
Posts: 637
Location: Penndel, PA [USA]
crc
There are many, many ways to handle file systems. I use a simple block-based file system (1k blocks), where a file gets an entry like:

Code:
rb 32 ; filename
dd starting_block
dd number_of_blocks    


It's very simple, and quite effective for a small OS.

Your idea would works just as easily the other way: have each block know the location of the next block. You'd have a chain of blocks, with some metadata in each block, and terminate the chain with "0" or something like that. Then you could read the file in the correct order and still only have the name & initial block number in the FAT Smile
Post 03 Nov 2004, 22:40
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joachim_neu



Joined: 22 Dec 2003
Posts: 139
joachim_neu
you can create every filesystem you want!!! i created my own, too, but the manual about it is in German... maybe i'll translate it.
Post 04 Nov 2004, 07:56
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Ghost Cat



Joined: 03 Nov 2004
Posts: 16
Ghost Cat
crc wrote:
Your idea would works just as easily the other way: have each block know the location of the next block.


Well, I don't know about your computer but mine is old and she can not predict the future. If I ask her to figure out where the blocks might fall she most likely will get beck to me with some sarcastic remark like "You want ME to guess?" Smile
Post 05 Nov 2004, 00:31
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Gomer73



Joined: 29 Nov 2003
Posts: 151
Gomer73
The problem with linking the blocks is slowness.
You read consecutive sectors off the disk straight into memory if the links aren't stored in the data, otherwise it is complicated or you have to do a lot of moves.
Post 05 Nov 2004, 16:17
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Ghost Cat



Joined: 03 Nov 2004
Posts: 16
Ghost Cat
Are you sure that it is how it's being done, the consecutive sectors are read in the batch, or is it your guess?
Post 10 Nov 2004, 15:02
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mastermind



Joined: 30 Jan 2004
Posts: 14
mastermind
No. They are.

Let's say you have a file on block 5.

How would you know where block 5 is? You follow the pointer in block 4.
But that assumes that you have block 4 in memory already. If not, you read block 4.

How would you know where block 4 is? You follow the pointer in block 3.
But that assumes that you have block 3 in memory already. If not, you read block 3.

How would you know where block 3 is? You follow the pointer in block 2.
But that assumes that you have block 2 in memory already. If not, you read block 2.

How would you know where block 2 is? You follow the pointer in block 1.
But that assumes that you have block 1 in memory already. If not, you read block 1.

Now that you have block 1, you can follow its pointer to block 2. You can then sequentially get blocks 3, 4, and 5. So you read _all_ of the blocks up to the desired block.

One way to reduce the amount of copying/moving is to use caching, in which you either store each block read somewhere in memory for future access or save only the pointer to each block. You still end up reading much of the disk.
Post 11 Nov 2004, 21:40
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joachim_neu



Joined: 22 Dec 2003
Posts: 139
joachim_neu
well, I think the biggest problem is, that the writing of all the files is easy, but what, if you delete a file? then there are for example 5 blocks in the middle free... and then they are only useable, if you make a moving with all the following files 5 blocks forward or wait for a file, which is 5 blocks big! much free memory is unuseable without movings...
Post 12 Nov 2004, 12:45
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mastermind



Joined: 30 Jan 2004
Posts: 14
mastermind
Not really.
This FS uses something like a linked list, which is really easy to manipulate (insert, delete, ...).

A file does not have to occupy sequential blocks. If each block has a link to the next block, then you can have a file A, for example that resides on blocks 1,5,2,3, and 9:

1->5->2->3->9

Removing a block is easy too, just set the pointer of the previous block to the next one. To insert involves a similar action.

Then, of course, you'd have to keep track of which blocks are free. Then you can have a block that holds a list of free blocks. If you need a block, just find a block here, link it in, and remove it from the list. If you delete a block, just return it to this list. Except, it's now getting closer to a FAT, except the table is for free blocks.


Last edited by mastermind on 12 Nov 2004, 13:22; edited 1 time in total
Post 12 Nov 2004, 13:18
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bubach



Joined: 17 Sep 2004
Posts: 340
Location: Trollhättan, Sweden
bubach
joachim_neu: I am thinking of this problem too. I'll have to figure that out, before i start implementing my own FS.
mastermind: I want all files to be in order, without fragmentation... Sad


Last edited by bubach on 13 Feb 2012, 14:56; edited 1 time in total
Post 12 Nov 2004, 13:20
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mastermind



Joined: 30 Jan 2004
Posts: 14
mastermind
You should keep using FAT until you have your new filesystem ready. Then you could make a driver or something. That way, your OS supports multiple filesystems, which is good.

Oh yeah. Bubach, I'm using your bootloader+secondstage for my own OS. I was using bootf02 before, but it was so tightly packed that I couldn't remove the paging code without breaking something (I wanted to do that in the kernel). Then I switched to GRUB, which wasn't good either, because I cannot execute any realmode code without either switching back into realmode or using v86. Your's was the only loader that I could successfully adapt for my purposes. Thanks!


Last edited by mastermind on 12 Nov 2004, 13:30; edited 1 time in total
Post 12 Nov 2004, 13:24
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bubach



Joined: 17 Sep 2004
Posts: 340
Location: Trollhättan, Sweden
bubach
Thats what i am doing.. Wink
Post 12 Nov 2004, 13:27
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mastermind



Joined: 30 Jan 2004
Posts: 14
mastermind
Hmm... Then perhaps once in a while, like in 10min intervals, you could run a diskgarbagecollect function or something. I cannot see any way right now to fix that problem.

Aiight. Gotta go to class now. bbl.
Post 12 Nov 2004, 13:32
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bubach



Joined: 17 Sep 2004
Posts: 340
Location: Trollhättan, Sweden
bubach
Yeah, i was thinking of doing some file-moving, when a specific size is needed. But i guess thats going to be slow. Installing software and get a 10min delay for file-moving.. Smile
Skip class? I (almost) only use school to get broadband access, as i live in the forrest.. Wink
Post 12 Nov 2004, 13:55
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Gomer73



Joined: 29 Nov 2003
Posts: 151
Gomer73
Sorry for not getting back sooner.
With LBA you can directly specify which memory locations to load the blocks to.
If you use links within the blocks, you would have to load the block into memory and the transfer the non-link stuff into the destination memory.

The speed would especially noticied for consecutive sectors in a row.

..Gome73
Post 12 Nov 2004, 17:53
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mastermind



Joined: 30 Jan 2004
Posts: 14
mastermind
Or you could do what toe programmers of MeOS did: read the whole disk into memory on bootup. It's faster to move stuff around in RAM. Then you could write everything to disk when the OS exits.

What do you mean, skip class? Smile Today I had first period free, so I could hack around, among other things...
Post 12 Nov 2004, 22:11
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joachim_neu



Joined: 22 Dec 2003
Posts: 139
joachim_neu
a clever idea, but if the OS breaks down? if there's a misstake or error, and the system reboots, all the work is away! and that's very bad! Or if you save when the misstake comes, you write the misstake on the floppy, too!
Post 13 Nov 2004, 09:23
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bubach



Joined: 17 Sep 2004
Posts: 340
Location: Trollhättan, Sweden
bubach
I don't think it's that clever.. only an attempt to get a slow asm os a bit faster.. Sad
ps: i don't mean to offend the menuet people, but menuet is slow for an asm os.


Last edited by bubach on 13 Feb 2012, 15:02; edited 1 time in total
Post 13 Nov 2004, 13:39
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ASHLEY4



Joined: 28 Apr 2004
Posts: 376
Location: UK
ASHLEY4
I agree with bubach, but i do not think its MenuetOS fault, you can not make a pmode, multitasking, OS using vesa, much faster.

PS: Is that slowwww pong games still in menuet ?.

\\\\||////
(@@)
ASHLEY4.

Batteries not included, Some assembly required.
Post 13 Nov 2004, 16:45
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mastermind



Joined: 30 Jan 2004
Posts: 14
mastermind
I don't know if it's still being distributed, but I still have it on my MeOS disk Wink.
Post 14 Nov 2004, 02:36
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