ntdb: enhancement to allow direct access to the ntdb map during expansion.

This means keeping the old mmap around when we expand the database.
We could revert to read/write, except for platforms with incoherent
mmap (ie. OpenBSD), where we need to use mmap for all accesses.

Thus we keep a linked list of old maps, and unmap them when the last access
finally goes away.

This is required if we want ntdb_parse_record() callbacks to be able
to expand the database.

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

1 files changed, 15 insertions, 4 deletions

diff --git a/lib/ntdb/private.h b/lib/ntdb/private.h
index 90b782d303..5efd2e0d92 100644
--- a/lib/ntdb/private.h
+++ b/lib/ntdb/private.h
@@ -301,6 +301,14 @@ struct ntdb_access_hdr {
 	bool convert;
 };
 
+/* mmaps we are keeping around because they are still direct accessed */
+struct ntdb_old_mmap {
+	struct ntdb_old_mmap *next;
+
+	void *map_ptr;
+	ntdb_len_t map_size;
+};
+
 struct ntdb_file {
 	/* How many are sharing us? */
 	unsigned int refcnt;
@@ -314,6 +322,12 @@ struct ntdb_file {
 	/* The file descriptor (-1 for NTDB_INTERNAL). */
 	int fd;
 
+	/* How many are accessing directly? */
+	unsigned int direct_count;
+
+	/* Old maps, still direct accessed. */
+	struct ntdb_old_mmap *old_mmaps;
+
 	/* Lock information */
 	pid_t locker;
 	struct ntdb_lock allrecord_lock;
@@ -429,7 +443,7 @@ void ntdb_io_init(struct ntdb_context *ntdb);
 void *ntdb_convert(const struct ntdb_context *ntdb, void *buf, ntdb_len_t size);
 
 /* Unmap and try to map the ntdb. */
-void ntdb_munmap(struct ntdb_file *file);
+enum NTDB_ERROR ntdb_munmap(struct ntdb_context *ntdb);
 enum NTDB_ERROR ntdb_mmap(struct ntdb_context *ntdb);
 
 /* Either alloc a copy, or give direct access.  Release frees or noop. */
@@ -576,9 +590,6 @@ struct ntdb_context {
 	enum NTDB_ERROR (*openhook)(int fd, void *data);
 	void *openhook_data;
 
-	/* Are we accessing directly? (debugging check). */
-	int direct_access;
-
 	/* Set if we are in a transaction. */
 	struct ntdb_transaction *transaction;