On Fri, Aug 13, 2010 at 01:47:01PM -0700, Joel Becker wrote:
> 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.
Wouldn't it rather be:
... ||
((last_fs_block >> (PAGE_CACHE_SHIFT - blocksize_bits)) >
(pgoff_t)(!0ULL))) {
Joel
--
"What no boss of a programmer can ever understand is that a programmer
is working when he's staring out of the window"
- With apologies to Burton Rascoe
Joel Becker
Consulting Software Developer
Oracle
E-mail: [email protected]
Phone: (650) 506-8127
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