Hello,

I am working on modifying my 2.4.20 linux kernel to do secure deletion of files.
I want to write zeros over the data blocks before a file is deleted. I have been trying to use the destroy_block() function(included at the bottom) to accomplish this.

Here's my original plan:
I wanted to call the destroy_block() function starting at the first data block of the file and use bh->b_next to traverse through all of the data blocks. I have put the destroy_block() function into inode.c and was calling destroy_block from ext2_truncate_all() which is my modified version of ext2_truncate(). I then called ext2_truncate_all() within ext2_unlink.
The problem that I ran into with this plan was that I could not figure out how to get to the first block of the file in order to pass it to destroy_block().

Alternative plan:
I read some newsgroup postings that told me that modifying truncate() is not a safe thing to do. So I tried putting the destroy_block() function in ext2_free_blocks() instead of calling it from ext2_unlink(). Unfortunately, this causes the system to freeze up whenever I try to write to the filesystem (ext2) that I am testing with.

I am hoping to get the secure delete working on ext2 first, then port it over to ext3 in order to take advantage of journaling.
At this point, I have hit a brick wall. I am not sure what to try next and was wondering if anyone could possibly point me in the right direction.

Thanks ahead of time,
Ken

static inline void destroy_block(struct inode *inode, unsigned long block)
{
struct buffer_head * bh;

bh = sb_getblk(inode->i_sb, block);
memset(bh->b_data, 0x00, bh->b_size);

mark_buffer_dirty(bh);
wait_on_buffer(bh);
brelse(bh);

return;
}