Re: [PATCH v3] nilfs2: implement calculation of free inodes count

[Vyacheslav Dubeyko <slava-yeENwD64cLxBDgjK7y7TUQ@public.gmane.org>]

Hi Ryusuke,

On Fri, 2013-05-17 at 01:44 +0900, Ryusuke Konishi wrote:
> On Thu, 16 May 2013 10:54:45 +0400, Vyacheslav Dubeyko wrote:
> > Hi Ryusuke,
> > 
> > On Thu, 2013-05-16 at 07:59 +0900, Ryusuke Konishi wrote:
> > 
> > [snip]
> >> > 
> >> > This patch still has a potential overflow issue that I pointed out in
> >> > the previous comment; the patch handles the number of descriptor
> >> > blocks in 32-bit wide variables without checking its upper limit.
> >> > 
> >> > If you won't to add checks for the number of descriptor blocks, I
> >> > propose you to change the definition of nilfs_palloc_groups_count() instead:
> >> > 
> >> >   static inline unsigned long
> >> >   nilfs_palloc_groups_count(const struct inode *inode)
> >> >   {
> >> > - 	return 1UL << (BITS_PER_LONG - (inode->i_blkbits + 3 /* log2(8) */));
> >> > + 	return nilfs_palloc_groups_per_desc_block(inode) << 32;
> >> >   }
> >> > 
> > 
> > I think the real reason of problem is in using constants (BITS_PER_LONG
> > for the first case and 32 for the second one). But, anyway, it makes
> > sense to operate by volume size in this calculation. Because namely
> > volume size is the real limitation for calculation of maximum available
> > groups count.
> > 
> > What do you think about using volume size in this calculation?
> > 
> > With the best regards,
> > Vyacheslav Dubeyko.
> 
> I disagree with using volume size because it makes resize logic much
> harder especially for shrink logic.  It requires reconstructing of
> ifile and DAT meatadata file.
> 
> I just want to fix the calculation of the maximum number of groups so
> that the number of descriptor blocks doesn't overflow both for 64-bit
> and 32-bit architectures.
> 

Ok. I see.

What about such implementation?

static inline unsigned long
nilfs_palloc_groups_count(const struct inode *inode)
{
#define NILFS_DESC_BLOCKS_MAX UINT_MAX
	return nilfs_palloc_groups_per_desc_block(inode) *
			(unsigned long)NILFS_DESC_BLOCKS_MAX;
#undef NILFS_DESC_BLOCKS_MAX
}

With the best regards,
Vyacheslav Dubeyko.

> Regards,
> Ryusuke Konishi
> 
> 
> >> > This implies the maximum number of descriptor block is 1 ^ 32.
> >> > 
> >> > Because the above diff changes the maximum number of groups, I think
> >> > it should be inserted as a separate patch.
> >> 
> >> Oops, sorry, this change can overflow in 32-bit architectures
> >> because the type of return value is still unsigned long.
> >> That calculation should be revised more carefully.
> >> 
> >> Ryusuke Konishi
> >> --
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> > 
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