On Fri, Aug 13, 2010 at 06:30:07PM +0200, Jan Kara wrote:
> On Thu 12-08-10 15:29:49, Joel Becker wrote:
> > +/**
> > + * generic_check_addressable - Check addressability of file system
> > + * @blocksize_bits: log of file system block size
> > + * @num_blocks: number of blocks in file system
> > + *
> > + * Determine whether a file system with @num_blocks blocks (and a
> > + * block size of 2**@blocksize_bits) is addressable by the sector_t
> > + * and page cache of the system. Return 0 if so and -EFBIG otherwise.
> > + */
> > +int generic_check_addressable(unsigned blocksize_bits, u64 num_blocks)
> > +{
> > + u64 last_fs_block = num_blocks - 1;
> > +
> > + if (unlikely(num_blocks == 0))
> > + return 0;
> > +
> > + if ((blocksize_bits < 9) || (blocksize_bits > PAGE_CACHE_SHIFT))
> > + return -EINVAL;
> > +
> > + if ((last_fs_block >
> > + (sector_t)(~0ULL) >> (blocksize_bits - 9)) ||
> > + (last_fs_block >
> > + (pgoff_t)(~0ULL) >> (PAGE_CACHE_SHIFT - blocksize_bits))) {
> ^^^ I don't get the pgoff_t check. Shouldn't it rather be
> (u64)(pgoff_t)(~0ULL) << (PAGE_CACHE_SHIFT - blocksize_bits)?
> Because on 32-bit arch we are able to address 16TB device, which is for 1KB
> blocksize 1<<34 blocks. But your math gives 1<<30 blocks...
This code is directly lifted from ext4. But that said, I am
starting to think you're right. 1 page == 4 x 1K blocks, rather than 4
pages == 1 1K block.
Joel
--
"I always thought the hardest questions were those I could not answer.
Now I know they are the ones I can never ask."
- Charlie Watkins
Joel Becker
Consulting Software Developer
Oracle
E-mail: joel.becker@xxxxxxxxxx
Phone: (650) 506-8127
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