Addressed reviewer's comments

Author: danielinux

config.h

@@ -8,7 +8,7 @@
 #define ETHERNET
 #define LINK_MTU 1536
 #ifndef LINK_MTU_MIN
-#define LINK_MTU_MIN 64
+#define LINK_MTU_MIN 64U
 #endif
 #if LINK_MTU < LINK_MTU_MIN
 #error "LINK_MTU must be greater than or equal to LINK_MTU_MIN"

docs/API.md

@@ -211,6 +211,7 @@ int wolfIP_mtu_get(struct wolfIP *s, unsigned int if_idx, uint32_t *mtu);
 Access the link-layer descriptor(s) that should be wired to hardware drivers. `_ex` returns `NULL` if `if_idx` exceeds `WOLFIP_MAX_INTERFACES`.
 `wolfIP_mtu_set()` updates the effective per-interface MTU, treating `0` as the default `LINK_MTU` and clamping to `[LINK_MTU_MIN, LINK_MTU]`. `wolfIP_mtu_get()` returns the effective MTU currently used by the stack.
 For `non_ethernet` devices this value remains the internal frame budget; the maximum IP bytes handed to the driver are reduced by `ETH_HEADER_LEN` when Ethernet support is compiled in.
+- Returns: `wolfIP_getdev()`/`wolfIP_getdev_ex()` return a pointer to the link-layer descriptor or `NULL` on invalid interface index; `wolfIP_mtu_set()` returns `0` on success or a negative error code on failure; `wolfIP_mtu_get()` returns `0` on success or a negative error code on failure and stores the effective MTU in `*mtu`.
 
 ## DHCP Client Functions
 

src/wolfip.c

@@ -1228,6 +1228,7 @@ static inline int tx_has_writable_space(const struct tsocket *t)
     return 0;
 }
 
+/* Effective link-layer frame budget after applying default/min/max clamping. */
 static inline uint32_t wolfIP_ll_frame_mtu(const struct wolfIP_ll_dev *ll)
 {
     uint32_t mtu;
@@ -1242,18 +1243,22 @@ static inline uint32_t wolfIP_ll_frame_mtu(const struct wolfIP_ll_dev *ll)
     return mtu;
 }
 
+/* Per-interface wrapper around the clamped link-layer frame MTU helper. */
 static inline uint32_t wolfIP_frame_mtu(struct wolfIP *s, unsigned int if_idx)
 {
     return wolfIP_ll_frame_mtu(wolfIP_ll_at(s, if_idx));
 }
 
+/* IP payload MTU derived from the frame budget after removing link overhead. */
 static inline uint32_t wolfIP_ip_mtu(struct wolfIP *s, unsigned int if_idx)
 {
     uint32_t mtu = wolfIP_frame_mtu(s, if_idx);
 
     if (mtu <= ETH_HEADER_LEN)
         return 0;
     mtu -= ETH_HEADER_LEN;
+    /* Frame MTU may exceed the IPv4 payload maximum (e.g. 1536-byte link
+     * frames), but IP payload MTU remains capped at the standard 1500 bytes. */
     if (mtu > IP_MTU_MAX)
         mtu = IP_MTU_MAX;
     return mtu;
@@ -5290,8 +5295,6 @@ static void arp_queue_packet(struct wolfIP *s, unsigned int if_idx, ip4 dest,
 
     if (!s || len == 0)
         return;
-    if (len > LINK_MTU)
-        return;
     if (len > wolfIP_frame_mtu(s, if_idx))
         return;