From 90b211fa2da3f36939e84b6426988832a62caf4b Mon Sep 17 00:00:00 2001 From: Kent Overstreet Date: Tue, 30 Jul 2024 20:35:59 -0400 Subject: bcachefs: Add a comment for bucket helper types We've had bugs in the past with incorrect integer conversions in disk accounting code, which is why bucket helpers now always return s64s; add a comment explaining this. Signed-off-by: Kent Overstreet --- fs/bcachefs/alloc_background.h | 8 ++++++++ 1 file changed, 8 insertions(+) (limited to 'fs') diff --git a/fs/bcachefs/alloc_background.h b/fs/bcachefs/alloc_background.h index f13e619b4b21..96a0444ea78f 100644 --- a/fs/bcachefs/alloc_background.h +++ b/fs/bcachefs/alloc_background.h @@ -82,6 +82,14 @@ static inline bool bucket_data_type_mismatch(enum bch_data_type bucket, bucket_data_type(bucket) != bucket_data_type(ptr); } +/* + * It is my general preference to use unsigned types for unsigned quantities - + * however, these helpers are used in disk accounting calculations run by + * triggers where the output will be negated and added to an s64. unsigned is + * right out even though all these quantities will fit in 32 bits, since it + * won't be sign extended correctly; u64 will negate "correctly", but s64 is the + * simpler option here. + */ static inline s64 bch2_bucket_sectors_total(struct bch_alloc_v4 a) { return a.stripe_sectors + a.dirty_sectors + a.cached_sectors; -- cgit v1.2.3-70-g09d2