Re: Access content of file via inodes

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

> Looking at reiserfs code in the current 2.6 kernel it does:
> 
> .bmap = reiserfs_aop_bmap,
> 
> Which is:
> 
> static sector_t reiserfs_aop_bmap(struct address_space *as, sector_t
> block) {
>   return generic_block_bmap(as, block, reiserfs_bmap) ;
> }
> 
> And generic_block_bmap is:
> 
> sector_t generic_block_bmap(struct address_space *mapping, sector_t
> block,
>                             get_block_t *get_block)
> {
>         struct buffer_head tmp;
>         struct inode *inode = mapping->host;
>         tmp.b_state = 0;
>         tmp.b_blocknr = 0;
>         get_block(inode, block, &tmp, 0);
>         return tmp.b_blocknr;
> }
> 
> It ignores any errors from get_block() and always returns tmp.b_blocknr.
> Thus is get_block() fails, tmp.b_blocknr is 0 and hence 0 is returned,
> i.e. a sparse block.  Which is complete rubbish...
> 
> And get_block in this case in reiserfs is:
> 
> static int reiserfs_bmap (struct inode * inode, sector_t block,
>                           struct buffer_head * bh_result, int create)
> {
>     if (!file_capable (inode, block))
>         return -EFBIG;
> 
>     reiserfs_write_lock(inode->i_sb);
>     /* do not read the direct item */
>     _get_block_create_0 (inode, block, bh_result, 0) ;
>     reiserfs_write_unlock(inode->i_sb);
>     return 0;
> }

Just wondering. Say, reiserfs/r4, how is it possible to access
the tail which contain the data of the file, since most of our
production boxes uses either reiserfs and/or reiser4.

Kathy