Pbuf struct of LWIP protocol stack

The pbuf struct is located in src/include/LWIP/pbuf. h.

The data received by the Ethernet interruption is first stored in the data link composed of the structure, and then delivered to the upper-layer protocol.

This struct can be said to be ubiquitous.

Struct pbuf {/** next pbuf in singly linked pbuf chain points to the next pbuf */struct pbuf * next; /** pointer to the actual data in the buffer points to the valid data zone */void * payload; /*** total length of this buffer and all next buffers in chain * belonging to the same packet. * Total data link length * for non-queue packet chains this is the invariant: * P-> tot_len = p-> Len + (p-> next? P-> next-> tot_len: 0) */u16_t tot_len;/** length of this buffer */u16_t Len; /** pbuf_type as u8_t instead of Enum to save space pbuf type, including pbuf_ram, pbuf_rom, pbuf_ref, and pbuf_pool, these types indicate the Data Type pointed to by the pointer payload */u8_t/* pbuf_type */type;/** MISC flags mixed flag bits, each representing a flag */u8_t flags; /*** the reference count always equals the number of pointers * that refer to this pbuf. this can be pointers from an application, * the stack itself, or pbuf-> next pointers from a chain. count the number of pointers pointing to this pbuf. these pointers may be applied. Program The pointer of the protocol stack, or the pbuf-> next pointer in the data link. The pbuf */u16_t ref can be released only when the ref is 0; # If lwip_ptpd // If the precision clock synchronization protocol standard of the Network Measurement and Control System is enabled/* the time at which the packet was received, seconds component */u32_t time_s; /* the time at which the packet was received, nanoseconds component */u32_t time_ns; # endif/* # If lwip_ptpd */};