zebra: add new CLI args "block-len" and "node-len"

In the current implementation, an SRv6 locator only supports the
following structure:
* node-len = 24
* block-len = prefix-len - 24
* function-len = <configurable>
* argument-len = 0

This commit adds two optional arguments to the locator_prefix CLI
command: "node-len" and "block-len". These arguments allows an user to
configure the block length and node length of a SRv6 locator according
to the following logic:
* the node-len + block-len = prefix-len constraint must always be
satisfied;
* if node-len and block-len are both omitted, they are calculated as in
the current implementation (for backward compatibility reasons)
* if node-len is omitted, its value is computed as
prefix-len - block-len
* if block-len is omitted, its value is computed as
prefix-len - node-len

Signed-off-by: Carmine Scarpitta <carmine.scarpitta@uniroma2.it>

1 files changed, 27 insertions, 25 deletions

diff --git a/zebra/zebra_srv6_vty.c b/zebra/zebra_srv6_vty.c
index daac4cade0..b9ad3821a1 100644
--- a/zebra/zebra_srv6_vty.c
+++ b/zebra/zebra_srv6_vty.c
@@ -271,42 +271,44 @@ DEFUN (no_srv6_locator,
 
 DEFPY (locator_prefix,
        locator_prefix_cmd,
-       "prefix X:X::X:X/M$prefix [func-bits (0-64)$func_bit_len]",
+       "prefix X:X::X:X/M$prefix [func-bits (0-64)$func_bit_len] \
+	       [block-len (16-64)$block_bit_len] [node-len (16-64)$node_bit_len]",
        "Configure SRv6 locator prefix\n"
        "Specify SRv6 locator prefix\n"
        "Configure SRv6 locator function length in bits\n"
-       "Specify SRv6 locator function length in bits\n")
+       "Specify SRv6 locator function length in bits\n"
+       "Configure SRv6 locator block length in bits\n"
+       "Specify SRv6 locator block length in bits\n"
+       "Configure SRv6 locator node length in bits\n"
+       "Specify SRv6 locator node length in bits\n")
 {
 	VTY_DECLVAR_CONTEXT(srv6_locator, locator);
 	struct srv6_locator_chunk *chunk = NULL;
 	struct listnode *node = NULL;
 
-	if (prefix->prefixlen != 64) {
-		vty_out(vty,
-			"%% Invalid argument: Unsupported locator format\n");
-		return CMD_WARNING_CONFIG_FAILED;
-	}
-
 	locator->prefix = *prefix;
 	func_bit_len = func_bit_len ?: ZEBRA_SRV6_FUNCTION_LENGTH;
 
-	/*
-	 * TODO(slankdev): please support variable node-bit-length.
-	 * In draft-ietf-bess-srv6-services-05#section-3.2.1.
-	 * Locator block length and Locator node length are defined.
-	 * Which are defined as "locator-len == block-len + node-len".
-	 * In current implementation, node bits length is hardcoded as 24.
-	 * It should be supported various val.
-	 *
-	 * Cisco IOS-XR support only following pattern.
-	 *  (1) Teh locator length should be 64-bits long.
-	 *  (2) The SID block portion (MSBs) cannot exceed 40 bits.
-	 *      If this value is less than 40 bits,
-	 *      user should use a pattern of zeros as a filler.
-	 *  (3) The Node Id portion (LSBs) cannot exceed 24 bits.
-	 */
-	locator->block_bits_length = ZEBRA_SRV6_LOCATOR_BLOCK_LENGTH;
-	locator->node_bits_length = ZEBRA_SRV6_LOCATOR_NODE_LENGTH;
+	/* Resolve optional arguments */
+	if (block_bit_len == 0 && node_bit_len == 0) {
+		block_bit_len =
+			prefix->prefixlen - ZEBRA_SRV6_LOCATOR_NODE_LENGTH;
+		node_bit_len = ZEBRA_SRV6_LOCATOR_NODE_LENGTH;
+	} else if (block_bit_len == 0) {
+		block_bit_len = prefix->prefixlen - node_bit_len;
+	} else if (node_bit_len == 0) {
+		node_bit_len = prefix->prefixlen - block_bit_len;
+	} else {
+		if (block_bit_len + node_bit_len != prefix->prefixlen) {
+			vty_out(vty,
+				"%% block-len + node-len must be equal to the selected prefix length %d\n",
+				prefix->prefixlen);
+			return CMD_WARNING_CONFIG_FAILED;
+		}
+	}
+
+	locator->block_bits_length = block_bit_len;
+	locator->node_bits_length = node_bit_len;
 	locator->function_bits_length = func_bit_len;
 	locator->argument_bits_length = 0;