Hi, all
when I read ext3_readpage function following
ext3_readpage->mpage_readpage->do_mpage_readpage, there are:
nblocks = map_bh->b_size >> blkbits;
if (buffer_mapped(map_bh) && block_in_file > *first_logical_block &&
block_in_file < (*first_logical_block + nblocks)) {
unsigned map_offset = block_in_file - *first_logical_block;
unsigned last = nblocks - map_offset;
for (relative_block = 0; ; relative_block++) {
if (relative_block == last) {
clear_buffer_mapped(map_bh);
break;
}
if (page_block == blocks_per_page)
break;
blocks[page_block] = map_bh->b_blocknr + map_offset +
relative_block;
page_block++;
block_in_file++;
}
bdev = map_bh->b_bdev;
}
Since map_bh->b_size is the size of the block buffer, and blkbits is
associated with the block in inode, why does he do the operation >> ?
And what is the meaning and usage of first_logical_block? the initial
value of it is 0.
Hope someone will help me!
Thanks!
--
National Research Center for Intelligent Computing Systems
Institute of Computing Technology, Chinese Academy of Sciences
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