Re: Access content of file via inodes

["Kathy KN (HK)" <kathy.kn@xxxxxxxxx>]

Hi Nitin,

I did a simple test to see if b_data points to the actual data of the
file/inode.
I am using ext2 (non-journaling fs) for my test partition.

...
Apr  x 1x:50:50 x kernel: vfs_unlink: blkbits[12], blks_per_pg[1],
pblock[0], lblock[26]
Apr  x 1x:50:50 x kernel: vfs_unlink: memset bh->b_data of block [@132130]
Apr  x 1x:50:50 x kernel: vfs_unlink: memset bh->b_data of block [@132131]
Apr  x 1x:50:50 x kernel: vfs_unlink: memset bh->b_data of block [@132132]
Apr  x 1x:50:50 x kernel: vfs_unlink: memset bh->b_data of block [@132133]
Apr  x 1x:50:50 x kernel: vfs_unlink: memset bh->b_data of block [@132134]
Apr  x 1x:50:50 x kernel: vfs_unlink: memset bh->b_data of block [@132135]
Apr  x 1x:50:50 x kernel: vfs_unlink: memset bh->b_data of block [@132136]
...

Looks like I managed to get the blocks that belong to this particular inode.
But when I try to zero b_data, the data still appears in the hard disk device
(verified using hexdump).

Any idea why? It's been troubling me for days.

Regards,
Kathy

On Apr 5, 2005 3:26 PM, nitin ahuja <nitin2ahuja@xxxxxxxxxxxxx> wrote:
> Hi,
> 
> >
> > How do I access/read the content of the files via                  > using inodes
> > or blocks that belong to the inode, at sys_link and    > vfs_link layer?
> > I used bmap to access the blocks that belongs to the   > inodes, but
> > getting access to the buffer_head's b_data doesn't      > seem to help.
> >
> 
> In struct buffer_head, b_data points to memory region of size 4K containing data of the desired block. So you can memcpy it to your buffer.
> 
> Nitin
> 
>

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