Signed-off-by: David Sterba <dsterba@xxxxxxxx> --- fs/btrfs/struct-funcs.c | 29 ++++++++++++++++------------- 1 file changed, 16 insertions(+), 13 deletions(-) diff --git a/fs/btrfs/struct-funcs.c b/fs/btrfs/struct-funcs.c index 225ef6d7e949..1021b80f70db 100644 --- a/fs/btrfs/struct-funcs.c +++ b/fs/btrfs/struct-funcs.c @@ -39,23 +39,26 @@ static bool check_setget_bounds(const struct extent_buffer *eb, } /* - * this is some deeply nasty code. + * Macro templates that define helpers to read/write extent buffer data of a + * given size, that are also used via ctree.h for access to item members via + * specialized helpers. * - * The end result is that anyone who #includes ctree.h gets a - * declaration for the btrfs_set_foo functions and btrfs_foo functions, - * which are wrappers of btrfs_set_token_#bits functions and - * btrfs_get_token_#bits functions, which are defined in this file. + * Generic helpers: + * - btrfs_set_8 (for 8/16/32/64) + * - btrfs_get_8 (for 8/16/32/64) * - * These setget functions do all the extent_buffer related mapping - * required to efficiently read and write specific fields in the extent - * buffers. Every pointer to metadata items in btrfs is really just - * an unsigned long offset into the extent buffer which has been - * cast to a specific type. This gives us all the gcc type checking. + * Generic helpes with a token, caching last page address: + * - btrfs_set_token_8 (for 8/16/32/64) + * - btrfs_get_token_8 (for 8/16/32/64) * - * The extent buffer api is used to do the page spanning work required to - * have a metadata blocksize different from the page size. + * The set/get functions handle data spanning two pages transparently, in case + * metadata block size is larger than page. Every pointer to metadata items is + * an offset into the extent buffer page array, cast to a specific type. This + * gives us all the type checking. * - * There are 2 variants defined, one with a token pointer and one without. + * The extent buffer pages stored in the array pages do not form a contiguous + * range, but the API functions assume the linear offset to the range from + * 0 to metadata node size. */ #define DEFINE_BTRFS_SETGET_BITS(bits) \ -- 2.25.0
