Documentation/block/writeback_cache_control.rst

23 The REQ_PREFLUSH flag can be OR ed into the r/w flags of a bio submitted from
27 storage before the flagged bio starts. In addition the REQ_PREFLUSH flag can be
44 Filesystems can simply set the REQ_PREFLUSH and REQ_FUA bits and do not have to
46 the Forced Unit Access is implemented.  The REQ_PREFLUSH and REQ_FUA flags
53 These drivers will always see the REQ_PREFLUSH and REQ_FUA bits as they sit
56 to be implemented for bios with the REQ_PREFLUSH bit set.  For real device
57 drivers that do not have a volatile cache the REQ_PREFLUSH and REQ_FUA bits
58 on non-empty bios can simply be ignored, and REQ_PREFLUSH requests without
68 support required, the block layer completes empty REQ_PREFLUSH requests before
69 entering the driver and strips off the REQ_PREFLUSH and REQ_FUA bits from
77 REQ_PREFLUSH requests with a payload are automatically turned into a sequence