Hi, Recently I'm trying to implement a write-intent bitmap for btrfs to address its write-hole problems for RAID56. (In theory, btrfs only needs to know where the partial stripe write doesn't finish properly, and do a mandatory scrub for those stripes before mount to address it). My initial assumption for write-intent bitmap is, before any write can be submitted, corresponding bit(s) must be set in the bitmap, and the bitmap must be flushed to disk, then the bio can really be submitted. Thus functions like md_bitmap_startwrite() should not only set the bits, but also submit and flush the bio. (With some bio plug to optimize). But to my surprise, md_bitmap_startwrite() really just set the bitmap, no obvious submit/flush path. Is my assumption on write-intent bitmap completely wrong, or is there some special handling for md write-intent bitmap? Thanks, Qu
