dummy fs

dummy fs

[Jan Koss]

Hello.

I want implement educational file-system for Linux.
I suppose it would be very simplified UFS (for example,
with such limitations like: size of file <=8K, length of name <20 characters
and so on). The main goal is simplicity, small size of implementation
and space for speedup improvements.

1)May be some one hear about such for Linux 2.6 ?

2)Currently I'm investigating how "truncate" method should works on
the filesystem layer.
Is any description how it should works?
I mean, as I understand first I should truncate page cache
(block_truncate_page?),
what about "buffer_head" which now not belong to my file and may be
used by another process at the same time?

3)As I see sb_find_get_block return "buffer_head", with b_count==2,
(if nobody before use this "buffer_head"),
is it right behavior?
Should I call two time brelse to free "buffer_head",
which I get using sb_find_get_block?

4)Is there set of tests to check work of ordinary Unix file-system?
For example: one process creates files, and another check using
(readdir) is all right,
one open file for writing, another open the same file for reading... etc

Re: dummy fs

[Tyler]

Jan Koss wrote:
> Hello.
> 
> I want implement educational file-system for Linux.
> I suppose it would be very simplified UFS (for example,
> with such limitations like: size of file <=8K, length of name <20 characters
> and so on). The main goal is simplicity, small size of implementation
> and space for speedup improvements.
> 
> 1)May be some one hear about such for Linux 2.6 ?
> 
> 2)Currently I'm investigating how "truncate" method should works on
> the filesystem layer.
> Is any description how it should works?
> I mean, as I understand first I should truncate page cache
> (block_truncate_page?),
> what about "buffer_head" which now not belong to my file and may be
> used by another process at the same time?
> 
> 3)As I see sb_find_get_block return "buffer_head", with b_count==2,
> (if nobody before use this "buffer_head"),
> is it right behavior?
> Should I call two time brelse to free "buffer_head",
> which I get using sb_find_get_block?
> 
> 4)Is there set of tests to check work of ordinary Unix file-system?
> For example: one process creates files, and another check using
> (readdir) is all right,
> one open file for writing, another open the same file for reading... etc
> -
Hi,

you can have a look at this page : 
http://wiki.kernelnewbies.org/NdevfsSource
it's the simplest ram filesystem.
or have a look at the ramfs.c file in the kernel tree.


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Re: dummy fs

[Greg KH]

On Thu, Jan 12, 2006 at 03:52:16PM +0100, Tyler wrote:
> you can have a look at this page : 
> http://wiki.kernelnewbies.org/NdevfsSource
> it's the simplest ram filesystem.

Ick, gotta love people taking your code and getting it wrong :(

I'll go update that page with the real ndevfs code so that no one copies
incorrect examples...

thanks,

greg k-h