tdb: handle processes dying during transaction commit.

tdb transactions were designed to be robust against the machine
powering off, but interestingly were never designed to handle the case
where an administrator kill -9's a process during commit.  Because
recovery is only done on tdb_open, processes with the tdb already
mapped will simply use it despite it being corrupt and needing
recovery.

The solution to this is to check for recovery every time we grab a
data lock: we could have gained the lock because a process just died.
This has no measurable cost: here is the time for tdbtorture -s 0 -n 1
-l 10000:

Before:
	2.75 2.50 2.81 3.19 2.91 2.53 2.72 2.50 2.78 2.77 = Avg 2.75

After:
	2.81 2.57 3.42 2.49 3.02 2.49 2.84 2.48 2.80 2.43 = Avg 2.74

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

1 files changed, 1 insertions, 0 deletions

diff --git a/lib/tdb/common/tdb_private.h b/lib/tdb/common/tdb_private.h
index f086e7d905..a0e3f20b4e 100644
--- a/lib/tdb/common/tdb_private.h
+++ b/lib/tdb/common/tdb_private.h
@@ -249,6 +249,7 @@ int tdb_ofs_read(struct tdb_context *tdb, tdb_off_t offset, tdb_off_t *d);
 int tdb_ofs_write(struct tdb_context *tdb, tdb_off_t offset, tdb_off_t *d);
 int tdb_lock_record(struct tdb_context *tdb, tdb_off_t off);
 int tdb_unlock_record(struct tdb_context *tdb, tdb_off_t off);
+bool tdb_needs_recovery(struct tdb_context *tdb);
 int tdb_rec_read(struct tdb_context *tdb, tdb_off_t offset, struct tdb_record *rec);
 int tdb_rec_write(struct tdb_context *tdb, tdb_off_t offset, struct tdb_record *rec);
 int tdb_do_delete(struct tdb_context *tdb, tdb_off_t rec_ptr, struct tdb_record *rec);