[Cluster-devel] [PATCH 08/27] iomap: add the new iomap_iter model

[Christoph Hellwig]

On Mon, Jul 19, 2021 at 09:56:00AM -0700, Darrick J. Wong wrote:
> Linus previously complained to me about filesystem code (especially
> iomap since it was "newer") (ab)using loff_t variables to store the
> lengths of byte ranges.  It was "loff_t length;" (or so willy
> recollects) that tripped him up.
> 
> ISTR he also said we should use size_t for all lengths because nobody
> should do operations larger than ~2G, but I reject that because iomap
> has users that iterate large ranges of data without generating any IO
> (e.g. fiemap, seek, swapfile activation).
> 
> So... rather than confusing things even more by mixing u64 and ssize_t
> for lengths, can we introduce a new 64-bit length typedef for iomap?
> Last summer, Dave suggested[1] something like:
> 
> 	typedef long long lsize_t;
> 
> That would enable cleanup of all the count/size/length parameters in
> fs/remap_range.c and fs/xfs/xfs_reflink.c to use the new 64-bit length
> type, since those operations have never been limited to 32-bit sizes.

I'd rather avoid playing guinea pig for a somewhat odd new type.  For
now I've switched it to the loff_t as that matches the rest of iomap.
If we switch away either to a new type or s64/u64 we should probably do
it as a big sweep.