On Fri, May 08, 2020 at 12:33:08AM +0300, Nikolay Borisov wrote: > On 7.05.20 г. 23:20 ч., David Sterba wrote: > > 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: > > nit: missing 'r' in 'helpers'. Without having looked into the code It's > not obvious what a "token" is in this context, is it worth it perhaps > documenting? ( I will take a look later and see if it's self-evident). I could write it as "Generic helpers with a token (a structure caching the address of most recently accessed page)" The use of 'last' is confusing as it's not the last as in the array. > > + * - 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 > ^^^^^ > nit: s/metadata/btree/? The terms should be interchangeable, but in the previous sentence it's 'metadata' and this one continues, so I wonder how would 'btree' fit here. All the structures here are on the higher level, so metadata etc, while b-tree node is the storage. > > + * 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 > > nit: "contiguous physical range" Ok. > > + * 0 to metadata node size. > > */ > > > > #define DEFINE_BTRFS_SETGET_BITS(bits) \ > >
