diff options
Diffstat (limited to 'fs/btrfs/struct-funcs.c')
| -rw-r--r-- | fs/btrfs/struct-funcs.c | 21 |
1 files changed, 21 insertions, 0 deletions
diff --git a/fs/btrfs/struct-funcs.c b/fs/btrfs/struct-funcs.c index ad03a32d1116..cdedbe144d45 100644 --- a/fs/btrfs/struct-funcs.c +++ b/fs/btrfs/struct-funcs.c @@ -17,6 +17,27 @@ */ #include <linux/highmem.h> + +/* this is some deeply nasty code. ctree.h has a different + * definition for this BTRFS_SETGET_FUNCS macro, behind a #ifndef + * + * The end result is that anyone who #includes ctree.h gets a + * declaration for the btrfs_set_foo functions and btrfs_foo functions + * + * This file declares the macros and then #includes ctree.h, which results + * in cpp creating the function here based on the template below. + * + * 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. + * + * The extent buffer api is used to do all the kmapping and page + * spanning work required to get extent buffers in highmem and have + * a metadata blocksize different from the page size. + */ + #define BTRFS_SETGET_FUNCS(name, type, member, bits) \ u##bits btrfs_##name(struct extent_buffer *eb, \ type *s) \ |
