virtual file system in pascal/delphi

[Brainer]

Nice you're interested in it, but please don't use it just now as it's really bad and needs to be fixed. It's released under BSD license.

[Rahakasvi]

Great I have no need to use it now, but perhaps later. I hope you can finish this project

I see that with this technique you will be generating a lot of fragmentation, especially when using that to game development One wishlist for features would be defragment button, that completely rewrites the archive.

[noeska]

So we have 2 vfs for delphi/fpc now? Nice

I am currently waiting for feedback before making changes to it again. One planned feature is closing the archive file after a user is finished reading/writing and opening again when needed. Also my example should be updated to something nice looking as Brainer's. Now some featurs available are not visible.

And yes defragmentation is an issue.

[Brainer]

@noeska: Yip, it seems like it's getting interesting now.

@Rahakasvi: The idea of a VFS is to simulate a real hard disk, and AFAIK fragmentation cannot be avoided, so yes, sooner or later it'll be necessary to defragment your files. Defragmentation will be available in the new release of the VFS.

The main design flaw of my VFS was that blocks information is stored in memory, so it's impossible to have huge drives. Now I'm working on a new design and a new file structure to make the VFS more flexible and faster. Also, I'd like to use that VFS for real data backups in the future, so I must make it reliable enough. I'll try to keep you posted - to anyone who's interested.

[noeska]

You read the complete archive in memory first? In my first version i also played with the idea of using a real record structure for an block and read that as a whole in memory but decided against it. Now if you need one byte from an file inside an archive only that byte is read not the complete block that the byte is stored in. The same goes for writing.

function TVirtualFileSystem.ReadBlock(ablockid: int64; var buffer; beginpos: integer; endpos: integer): int64;
var
  nextblockid: int64;
begin
  {$R+}
  FDataFile.Position :=(ablockid * FBlockSize); //goto begin of block
  FDataFile.ReadBuffer(nextblockid, sizeof(nextblockid));

  FDataFile.Position :=FDataFile.Position+beginpos; //advance to position within block
  FDataFile.ReadBuffer(buffer, (endpos-beginpos) ); //only read bytes needed

  result := nextblockid; //return the next block
end;

[Brainer]

Nope, files aren't loaded into memory, only data about blocks (i.e. block's flag and size). And you can't have a High(Cardinal) of them when you store it in memory.