Re: ext3 structure mapping to block device

[ajit mote <mail2blackmen@xxxxxxxxx>]

On Mon, Aug 17, 2009 at 11:38 AM, Manish Katiyar <mkatiyar@xxxxxxxxx> wrote:

On Mon, Aug 17, 2009 at 11:06 AM, ajit mote<mail2blackmen@xxxxxxxxx> wrote:
>
> Hello,
>
> I would like to know how file system structures are mapped to hard disk
> sector.

Each filesystem deals in the granularity of "block size" which is
generally configurable (typically 4K) during fs creation time. So each
block maps to 8 sectors (which are generally 512 bytes). Now given a
block number you can multiply it by 8 to get your hard disk sector.

 This is the starting point which I am looking for , you pointed exactly the same ...

 Any document which describes above in details will be great ....

> My goal is to understand how file system is created on block device
> and how superblocks are mapped to hard disk sectors.

Filesystem is created using a userspace binary (mke2fs for example in
case of ext2). Appropriate datastructures are written at appropiate
places during the FS creation time. See the sources of mkfs.c in
e2fsprogs.

I reached here , already downloaded the source for e2fsck package and playing with it ....
 

Superblock will have a predefined block number where it resides. From
the above calculation you can know which sector to read.

I can read the superblock content(will write small module) using superblock operation pointed :
http://lxr.linux.no/#linux+v2.6.30.4/fs/ext3/super.c
 

>
> I am not sure whether I stated the problem precisely or not but if I did not
> described it properly then let me know.

I am not sure if that answers your question correctly  :-) . If not
please let me know.

You answered what i needed at this time ... Thanks
 

Thanks -
Manish

>
> This is just an understanding sort of issue which I am looking for teaching
> purpose.
>
> Note:
>   Please free to change the subject line if not proper.
>
> --
> Thanks & Regards,
> Ajit Subhash Mote
>
>

--
Thanks -
Manish

-- 
Thanks & Regards,
Ajit Subhash Mote