DRBR(9)

💖 DRBR(9) — network driver interface to buf_ring

okay bestie, welcome to the DRBR(9) page from the Kernel Developer's Manual ✨ this one is all about the drbr squad and how network drivers use buf_ring(9) for enqueueing and dequeueing packets. stay with me, it’s actually iconic.

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🌸 NAME 🌸

drbr, drbr_free, drbr_enqueue, drbr_dequeue, drbr_dequeue_cond, drbr_flush, drbr_empty, drbr_inuse — network driver interface to buf_ring

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✨ SYNOPSIS ✨

#include <sys/param.h>
#include <net/if.h>
#include <net/if_var.h>

void
drbr_free(struct buf_ring *br, struct malloc_type *type);

int
drbr_enqueue(struct ifnet *ifp, struct buf_ring *br, struct mbuf *m);

struct mbuf *
drbr_dequeue(struct ifnet *ifp, struct buf_ring *br);

struct mbuf *
drbr_dequeue_cond(struct ifnet *ifp, struct buf_ring *br,
    int (*func) (struct mbuf *, void *), void *arg);

void
drbr_flush(struct ifnet *ifp, struct buf_ring *br);

int
drbr_empty(struct ifnet *ifp, struct buf_ring *br);

int
drbr_inuse(struct ifnet *ifp, struct buf_ring *br);

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💅 DESCRIPTION 💅

The drbr functions provide an API to network drivers for using buf_ring(9) for enqueueing and dequeueing packets. This is meant as a replacement for the IFQ interface for packet queuing. It allows a packet to be enqueued with a single atomic and packet dequeue to be done without any per-packet atomics as it is protected by the driver's tx queue lock. If INVARIANTS is enabled, drbr_dequeue() will assert that the tx queue lock is held when it is called.

🫶 lowkey important: that INVARIANTS assert is your vibe check for lock discipline, bestie.

• drbr_free() — frees all the enqueued mbufs and then frees the buf_ring.
• drbr_enqueue() — used to enqueue an mbuf to a buf_ring, falling back to the ifnet's IFQ if ALTQ(4) is enabled.
• drbr_dequeue() — used to dequeue an mbuf from a buf_ring or, if ALTQ(4) is enabled, from the ifnet's IFQ.
• drbr_dequeue_cond() — used to conditionally dequeue an mbuf from a buf_ring based on whether func returns TRUE or FALSE.
• drbr_flush() — frees all mbufs enqueued in the buf_ring and the ifnet's IFQ.
• drbr_empty() — returns TRUE if there are no mbufs enqueued, FALSE otherwise.
• drbr_inuse() — returns the number of mbufs enqueued.

😭 about drbr_inuse(): note to users that this is intrinsically racy as there is no guarantee that there will not be more mbufs when drbr_dequeue() is actually called. Provided the tx queue lock is held there will not be less.

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🔥 RETURN VALUES 🔥

• drbr_enqueue() returns ENOBUFS if there are no slots available in the buf_ring and 0 on success. slay.
• drbr_dequeue() and drbr_dequeue_cond() return an mbuf on success and NULL if the buf_ring is empty. no mbufs, no problem — you get NULL.

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🦋 HISTORY 🦋

These functions were introduced in FreeBSD 8.0. 🎀

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💌 source/version: Debian · date: September 27, 2012 · page: DRBR(9) — byeee bestie, go forth and queue responsibly 💖🫶✨