struct super_block {
struct list_head s_list; /* Keep this first */
dev_t s_dev; /* search index; _not_ kdev_t */
unsigned char s_blocksize_bits;
unsigned long s_blocksize;
...
from what I read, s_blocksize
and s_blocksize_bits
contain the size of the block in bytes and bits respectively.
the number of bits are bigger than the number of bytes, so wouldn't it make more sense if their types were the opposite way around? Like this:
unsigned char s_blocksize_bits;
unsigned long s_blocksize;
s_blocksize_bits
is not the size of the block in bits. It's the number of bits in the blocksize. If you search the code to see how it's used, it's often in bit shifting, e.g.
elen = (etype << 30) |
(elen +
(count << sb->s_blocksize_bits));
So, given a block number, you shift it by this many bits to get the corresponding offset (they assumed that blocks are always a power of 2 in size).