[PATCH v2] netfilter: nft_numgen: add increment counter offset value

[Laura Garcia Liebana]

Add support for an initialization counter value. With this option the
sysadmin is able to start the counter when used with the increment type.

Example:

        meta mark set numgen inc mod 2 sum 100

This will generate marks with the serie 100, 101, 100, 101, ...

Only supported for increment number generation.

Signed-off-by: Laura Garcia Liebana <nev...@gmail.com>
---
Changes in v2:
        - Separate _SUM_ changes with _until_ attribute renaming.

 include/uapi/linux/netfilter/nf_tables.h | 2 ++
 net/netfilter/nft_numgen.c               | 9 +++++++--
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/include/uapi/linux/netfilter/nf_tables.h 
b/include/uapi/linux/netfilter/nf_tables.h
index 24161e2..00a689d 100644
--- a/include/uapi/linux/netfilter/nf_tables.h
+++ b/include/uapi/linux/netfilter/nf_tables.h
@@ -1128,12 +1128,14 @@ enum nft_trace_types {
  * @NFTA_NG_DREG: destination register (NLA_U32)
  * @NFTA_NG_MODULUS: maximum counter value (NLA_U32)
  * @NFTA_NG_TYPE: operation type (NLA_U32)
+ * @NFTA_NG_SUM: Offset to initiate the counter (NLA_U32)
  */
 enum nft_ng_attributes {
        NFTA_NG_UNSPEC,
        NFTA_NG_DREG,
        NFTA_NG_MODULUS,
        NFTA_NG_TYPE,
+       NFTA_NG_SUM,
        __NFTA_NG_MAX
 };
 #define NFTA_NG_MAX    (__NFTA_NG_MAX - 1)
diff --git a/net/netfilter/nft_numgen.c b/net/netfilter/nft_numgen.c
index f51a3ed..a5ea3f7 100644
--- a/net/netfilter/nft_numgen.c
+++ b/net/netfilter/nft_numgen.c
@@ -44,6 +44,7 @@ static const struct nla_policy nft_ng_policy[NFTA_NG_MAX + 1] 
= {
        [NFTA_NG_DREG]          = { .type = NLA_U32 },
        [NFTA_NG_MODULUS]       = { .type = NLA_U32 },
        [NFTA_NG_TYPE]          = { .type = NLA_U32 },
+       [NFTA_NG_SUM]           = { .type = NLA_U32 },
 };
 
 static int nft_ng_inc_init(const struct nft_ctx *ctx,
@@ -51,13 +52,17 @@ static int nft_ng_inc_init(const struct nft_ctx *ctx,
                           const struct nlattr * const tb[])
 {
        struct nft_ng_inc *priv = nft_expr_priv(expr);
+       u32 sum = 0;
+
+       if (tb[NFTA_NG_SUM])
+               sum = ntohl(nla_get_be32(tb[NFTA_NG_SUM]));
 
        priv->modulus = ntohl(nla_get_be32(tb[NFTA_NG_MODULUS]));
-       if (priv->modulus == 0)
+       if (priv->modulus == 0 || sum >= priv->modulus)
                return -ERANGE;
 
        priv->dreg = nft_parse_register(tb[NFTA_NG_DREG]);
-       atomic_set(&priv->counter, 0);
+       atomic_set(&priv->counter, sum);
 
        return nft_validate_register_store(ctx, priv->dreg, NULL,
                                           NFT_DATA_VALUE, sizeof(u32));
-- 
2.8.1

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