dgraham at nortel
Jul 4, 2009, 11:29 AM
Post #1 of 1
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I was just looking over an old thread about MinixFs V3 support and
starting to get worried that my tweaks to support blocksizes of 512
bytes (for a small filesystem with many small files) might be broken.
This is the thread here: http://lkml.org/lkml/2006/5/6/50.
The nblocks() routine in fs/minix/itree_common.c now looks like this:
static inline unsigned nblocks(loff_t size, struct super_block *sb)
{
int k = sb->s_blocksize_bits - 10;
unsigned blocks, res, direct = DIRECT, i = DEPTH;
blocks = (size + sb->s_blocksize - 1) >> (BLOCK_SIZE_BITS + k);
...
and what had be worred at first is that sb->s_blocksize_bits will be 9
with a blocksize of 512, which makes k negative. But all may not be lost,
since k is only used once after this, after adding BLOCK_SIZE_BITS (10)
to it. At least that makes it nonnegative again, but then the question
is: what exactly is being accomplished here? First we subtract 10,
then add it back? The result is effectively this:
blocks = (size + sb->s_blocksize - 1) >> sb->s_blocksize_bits
which looks entirely correct to me. Is there any reason the code couldn't
just be written this way to begin with?
--Doug
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