On Sat 26-02-22 10:30:31, Zhang Yi wrote:
> On 2022/2/25 20:38, Jan Kara wrote:
> > On Fri 25-02-22 18:28:37, Zhang Yi wrote:
> >> + /* Compute how many metadata blocks are needed */
> >> + meta_blocks = 1;
> >> + meta_blocks += 1 + ppb;
> >> + meta_blocks += 1 + ppb + ppb * ppb;
> >> + /* Does block tree limit file size? */
> >> + if (res + meta_blocks <= upper_limit)
> >> + goto check_lfs;
> >> +
> >> + res = upper_limit;
> >> + /* How many metadata blocks are needed for addressing upper_limit? */
> >> + upper_limit -= EXT4_NDIR_BLOCKS;
> >> + /* indirect blocks */
> >> + meta_blocks = 1;
> >> + upper_limit -= ppb;
> >> + /* double indirect blocks */
> >> + if (upper_limit < ppb * ppb) {
> >> + meta_blocks += 1 + DIV_ROUND_UP_ULL(upper_limit, ppb);
> >> + res -= meta_blocks;
> >> + goto check_lfs;
> >> + }
> >> + meta_blocks += 1 + ppb;
> >> + upper_limit -= ppb * ppb;
> >> + /* tripple indirect blocks for the rest */
> >> + meta_blocks += 1 + DIV_ROUND_UP_ULL(upper_limit, ppb) +
> >> + DIV_ROUND_UP_ULL(upper_limit, ppb*ppb);
> >> + res -= meta_blocks;
> >> +check_lfs:
> >> res <<= bits;
> >
> > Cannot this overflow loff_t again? I mean if upper_limit == (1 << 48) - 1
> > and we have 64k blocksize, 'res' will be larger than (1 << 47) and thus
> > res << 16 will be greater than 1 << 63 => negative... Am I missing
> > something?
> >
>
> If upper_limit==(1 << 48) - 1, we could address the whole data blocks, the 'res'
> is equal to EXT4_NDIR_BLOCKS + ppb + ppb*ppb + ((long long)ppb)*ppb*ppb, it's
> smaller than (1 << 43) - 1, so res << 16 is still smaller 1 << 59, so it cannot
> overflow loff_t again.
Indeed, sorry for confusion. Not sure where I did mistake in my math
previously.
Honza
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
