fabricd: reimplement LSP transmission logic

Before this commit, isisd/fabricd maintained a bitfield for each LSP
to track the SRM bit for each circuit, which specifies whether an LSP
needs to be sent on that circuit. Every second, it would scan over all
LSPs in `lsp_tick` and queue them up for transmission accordingly.

This design has two drawbacks: a) it scales poorly b) it adds
unacceptable latency to the update process: each router takes a random
amount of time between 0 and 1 seconds to forward an update. In a
network with a diamter of 10, it might already take 10 seconds for an
update to traverse the network.

To mitigate this, a new design was chosen. Instead of tracking SRM in a
bitfield, have one tx_queue per circuit and declare that an LSP is in
that queue if and only if it would have SRM set for that circuit.

This way, we can track SRM similarly as we did before, however, on
insertion into the LSP queue, we can add a timer for (re)transmission,
alleviating the need for a periodic scan with LSP tick and reducing the
latency for forwarding of updates.

Signed-off-by: Christian Franke <chris@opensourcerouting.org>

1 files changed, 2 insertions, 2 deletions

diff --git a/isisd/isis_lsp.h b/isisd/isis_lsp.h
index d531cb157..4e6379447 100644
--- a/isisd/isis_lsp.h
+++ b/isisd/isis_lsp.h
@@ -37,7 +37,6 @@ struct isis_lsp {
 		struct list *frags;
 		struct isis_lsp *zero_lsp;
 	} lspu;
-	uint32_t SRMflags[ISIS_MAX_CIRCUITS];
 	uint32_t SSNflags[ISIS_MAX_CIRCUITS];
 	int level;     /* L1 or L2? */
 	int scheduled; /* scheduled for sending */
@@ -100,6 +99,7 @@ void lsp_print(struct isis_lsp *lsp, struct vty *vty, char dynhost);
 void lsp_print_detail(struct isis_lsp *lsp, struct vty *vty, char dynhost);
 int lsp_print_all(struct vty *vty, dict_t *lspdb, char detail, char dynhost);
 /* sets SRMflags for all active circuits of an lsp */
-void lsp_set_all_srmflags(struct isis_lsp *lsp);
+void lsp_set_all_srmflags(struct isis_lsp *lsp, bool set);
+void lsp_flood(struct isis_lsp *lsp, struct isis_circuit *circuit);
 
 #endif /* ISIS_LSP */