md/bcache/journal.h

9  * never spans two buckets. This means (not implemented yet) we can resize the
15  * We also keep some things in the journal header that are logically part of the
20  * rewritten when we want to move/wear level the main journal.
22  * Currently, we don't journal BTREE_REPLACE operations - this will hopefully be
25  * moving gc we work around it by flushing the btree to disk before updating the
35  * We track this by maintaining a refcount for every open journal entry, in a
38  * zero, we pop it off - thus, the size of the fifo tells us the number of open
41  * We take a refcount on a journal entry when we add some keys to a journal
42  * entry that we're going to insert (held by struct btree_op), and then when we
43  * insert those keys into the btree the btree write we're setting up takes a
48  * might contain keys for many journal entries - we handle this by making sure
55  * journal entries; from that and the current journal sequence number we compute
56  * last_seq - the oldest journal entry we still need. We write last_seq in each
57  * journal entry, and we also have to keep track of where it exists on disk so
58  * we don't overwrite it when we loop around the journal.
60  * To do that we track, for each journal bucket, the sequence number of the
61  * newest journal entry it contains - if we don't need that journal entry we
62  * don't need anything in that bucket anymore. From that we track the last
63  * journal bucket we still need; all this is tracked in struct journal_device
68  * There are two ways the journal could fill up; either we could run out of
69  * space to write to, or we could have too many open journal entries and run out
71  * without any locking we can't safely resize that fifo, so we handle it the
74  * If the journal fills up, we start flushing dirty btree nodes until we can
80  * Only used for holding the journal entries we read in btree_journal_read()
90  * We put two of these in struct journal; we used them for writes to the
115 	/* Number of blocks free in the bucket(s) we're currently writing to */
132 	 * journal writes it contains - so we know when a bucket can be reused.
136 	/* Journal bucket we're currently writing to */