Virtual File System Functions

[Jeko]

Which functions I need to implement a good Virtual File System?

I have (for now) these funcions:

Code: Select all

read
write
open
close
readdir
finddir

[piranha]

fread, fopen, fclose, fwrite, fseek, etc.
stdio.h should give you some ideas.
-JL

[Jeko]

how can I implement the virtual file system?

Have you any guide or tutorial?

[JamesM]

Well actually, I happen to have one I cooked up earlier...

http://www.jamesmolloy.co.uk/tutorial_h ... nitrd.html

[Jeko]

Well actually, I happen to have one I cooked up earlier...

http://www.jamesmolloy.co.uk/tutorial_h ... nitrd.html

But I don't understand how can I open for example a file like '/usr/lib/file.txt' (if there is this file) with this method...

For example if I have the function open("/usr/lib/file.txt"), how can this function open the file?

(assuming this file exists)

[AJ]

Hi,

You need to have a VFS function which recurses through each path, stopping if it gets to a point where the next item does not exist. For example - first, check if 'usr' exists. If so, search the 'usr' directory for the 'lib' item. If that exists, find 'file.txt' and return a valid handle for that in the selected mode (read/write/append/etc...). If any stage of this fails, you stop and return an error code.

Although this isn't difficult, you need to think carefully about error checking, how errors are handled and exactly what mode types your OS will allow...

Cheers,
Adam

[JamesM]

Well actually, I happen to have one I cooked up earlier...

http://www.jamesmolloy.co.uk/tutorial_h ... nitrd.html

But I don't understand how can I open for example a file like '/usr/lib/file.txt' (if there is this file) with this method...

For example if I have the function open("/usr/lib/file.txt"), how can this function open the file?

(assuming this file exists)

That is actually explained in detail on that page - did you actually read it or just skim it?

[Jeko]

Hi,

You need to have a VFS function which recurses through each path, stopping if it gets to a point where the next item does not exist. For example - first, check if 'usr' exists. If so, search the 'usr' directory for the 'lib' item. If that exists, find 'file.txt' and return a valid handle for that in the selected mode (read/write/append/etc...). If any stage of this fails, you stop and return an error code.

Although this isn't difficult, you need to think carefully about error checking, how errors are handled and exactly what mode types your OS will allow...

Cheers,
Adam

It's the only method to do this?

[Jeko]

and how can, for example, I mount a filesystem somewhere?

[Jeko]

However I think I'll implement VFS functions same as FUSE.

[AJ]

It is pretty much the only method until you have some kind of inode cache, but I would suggest that it some time in the future.

For FS mounting and so on, please see JamesM's link.

Cheers,
Adam

[JamesM]

and how can, for example, I mount a filesystem somewhere?

Oh my God! It's in the link I posted! Do you not read?

[lukem95]

I think hes asking for a step by step

MarkOS, read the page james linked you to, SEVERAL TIMES. Then download the code, get it working, customise it so your sure you know how it works, and then re-think the question. I guarantee you you will have at least some of the answers then.

[Combuster]

Asking smart questions is part of the rules

[bewing]

I would add quite a few more, myself.

I'd say there need to be two versions of read and write -- one that does a buffered operation into a file descriptor buffer, and another that is filesystem specific for when you want to load/unload the file descriptor buffer. If you want to handle filesystems like mine, you even need a third (pre-read) read function that is called during the open() function.

You are going to need a routine to cache directory entries (as JamesM said); a routine to do sanity checks on raw directories, the full directory tree, and the inode structure; a defrag routine; a routine to return general info about the FS (volume name, # of free clusters and free inodes); a routine to allocate new "nodes" (directory or file) in the VFS; a routine to delete nodes, routines to allocate and free inodes; and, of course, open, close, finddir, readdir, seek, and stat.