On Tuesday 12 February 2008, David Miller wrote: > From: Chris Mason <chris.mason@xxxxxxxxxx> > Date: Mon, 11 Feb 2008 08:42:20 -0500 > > > The kernel is actually worse, because the set/get macros are more > > complex. Some live in ctree.h like in the progs, but the nasty ones live > > in struct-funcs.c > > This is really problematic, because you've got these things called > "btrfs_item_ptr()" which really isn't a pointer, it's a relative > 'unsigned long' offset cast to a pointer. The source of this > seems to be btrfs_leaf_data(). > > And then those things get passed down into the SETGET functions! Explaining it won't make it pretty, but at least I can tell you what the code does. This is all part of the btrfs code that supports tree block sizes larger than a page. The extent_buffer code (extent_io.c) provides a read/write api into an extent_buffer based on offsets from the start of the multi-page buffer. That's where the relative unsigned long comes from. The part where I cast it to pointers is me trying to maintain type checking throughout the code. The pointers themselves are useless, they need to be matched with an extent_buffer to actually get to the bytes. There are a few parts where the SETGET funcs are open coded, mostly in very performance critical functions. Just look for lexxx_to_cpu > > Then deeper down we have terribly inconsistent things like > btrfs_item_nr_offset() and > btrfs_item_offset_nr(). Btree blocks have the offset of the item header from the start of the block and the offset of the item data. And, I'm very bad at naming. > > Sigh... I'll see what I can do. Thanks -chris - To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
