lib: create `frr_daemon_state_{load,save}`

These functions load daemon-specific persistent state from
`/var/lib/frr` and supersede open-coded variants of similar calls in
ospfd, ospf6d and isisd to save GR state and/or sequence numbers.

Unlike the open-coded variants, the save call correctly `fsync()`s the
saved data to ensure disk contents are consistent.

Signed-off-by: David Lamparter <equinox@opensourcerouting.org>

1 files changed, 4 insertions, 0 deletions

diff --git a/lib/command.c b/lib/command.c
index becba8452b..244bf86e8e 100644
--- a/lib/command.c
+++ b/lib/command.c
@@ -1633,6 +1633,10 @@ static int vty_write_config(struct vty *vty)
 	return CMD_SUCCESS;
 }
 
+/* cross-reference frr_daemon_state_save in libfrr.c
+ * the code there is similar but not identical (state files always use the same
+ * name for the new write, and don't keep a backup of previous state.)
+ */
 static int file_write_config(struct vty *vty)
 {
 	int fd, dirfd;