src: support for get element command

You need a Linux kernel >= 4.15 to use this feature.

This patch allows us to dump the content of an existing set.

 # nft list ruleset
 table ip x {
        set x {
                type ipv4_addr
                flags interval
                elements = { 1.1.1.1-2.2.2.2, 3.3.3.3,
                             5.5.5.5-6.6.6.6 }
        }
 }

You check if a single element exists in the set:

 # nft get element x x { 1.1.1.5 }
 table ip x {
        set x {
                type ipv4_addr
                flags interval
                elements = { 1.1.1.1-2.2.2.2 }
        }
 }

Output means '1.1.1.5' belongs to the '1.1.1.1-2.2.2.2' interval.

You can also check for intervals:

 # nft get element x x { 1.1.1.1-2.2.2.2 }
 table ip x {
        set x {
                type ipv4_addr
                flags interval
                elements = { 1.1.1.1-2.2.2.2 }
        }
 }

If you try to check for an element that doesn't exist, an error is
displayed.

 # nft get element x x { 1.1.1.0 }
 Error: Could not receive set elements: No such file or directory
 get element x x { 1.1.1.0 }
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^

You can also check for multiple elements in one go:

 # nft get element x x { 1.1.1.5, 5.5.5.10 }
 table ip x {
        set x {
                type ipv4_addr
                flags interval
                elements = { 1.1.1.1-2.2.2.2, 5.5.5.5-6.6.6.6 }
        }
 }

You can also use this to fetch the existing timeout for specific
elements, in case you have a set with timeouts in place:

 # nft get element w z { 2.2.2.2 }
 table ip w {
        set z {
                type ipv4_addr
                timeout 30s
                elements = { 2.2.2.2 expires 17s }
        }
 }

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 5 insertions, 0 deletions

diff --git a/include/expression.h b/include/expression.h
index 6f4edbf5..29dd0346 100644
--- a/include/expression.h
+++ b/include/expression.h
@@ -433,6 +433,11 @@ extern int set_to_intervals(struct list_head *msgs, struct set *set,
 			    unsigned int debug_mask, bool merge);
 extern void interval_map_decompose(struct expr *set);
 
+extern struct expr *get_set_intervals(const struct set *set,
+				      const struct expr *init);
+struct table;
+extern void get_set_decompose(struct table *table, struct set *set);
+
 extern struct expr *mapping_expr_alloc(const struct location *loc,
 				       struct expr *from, struct expr *to);
 extern struct expr *map_expr_alloc(const struct location *loc,