DRBR(9)

💖 DRBR(9) — the network driver interface to buf_ring, bestie 💖

okay so this is a page from the Kernel Developer's Manual and it's literally about how network drivers talk to buf_ring. buckle up, it's giving ✨kernel internals✨ but make it cute.

🌸 NAME 🌸

drbr, drbr_free, drbr_enqueue, drbr_dequeue, drbr_dequeue_cond, drbr_flush, drbr_empty, drbr_inuse — the network driver interface to buf_ring. that's the whole squad 🫶

✨ SYNOPSIS ✨

first you gotta bring the headers in, no cap:

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

and here's every single function, exactly as it is, don't @ me:

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);

👑 DESCRIPTION 👑

so the drbr functions hand network drivers an API for using buf_ring(9) to enqueue and dequeue packets. it's meant as a replacement for the IFQ interface for packet queuing, which is a glow-up fr fr. the way it works: a packet can be enqueued with a single atomic</>, and packet dequeue gets done without any per-packet atomics</> because it's protected by the driver's tx queue lock. efficient queen behavior 💅

ngl, if INVARIANTS is enabled, drbr_dequeue() will assert that the tx queue lock is held when it is called. so hold that lock, bestie. 🔒

• drbr_free() — frees all the enqueued mbufs, and then frees the buf_ring. clean sweep, iconic. 🧹
• drbr_enqueue() — used to enqueue an mbuf to a buf_ring, falling back to the ifnet's IFQ if ALTQ(4) is enabled. it's got a backup plan, we love a prepared queen. 🎀
• 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. conditional queen behavior ✨
• drbr_flush() — frees all mbufs enqueued in the buf_ring and the ifnet's IFQ. everything. gone. periodt. 💀
• drbr_empty() — returns TRUE if there are no mbufs enqueued, FALSE otherwise. simple. gorgeous. 🦋
• drbr_inuse() — returns the number of mbufs enqueued. ok but heads up, bestie:

⚠️ note to users: 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. so like… it's a vibe check, not a promise. 😭

🌈 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, just NULL 🫶

🎀 HISTORY 🎀

these functions were introduced in FreeBSD 8.0. vintage, but make it nostalgic 💜

okay that's the whole page, you ate that reading session fr fr 💅✨

this lil manual page came from Debian, dated September 27, 2012 — so if you ever need to cite it, that's the tea. mwah, go enqueue something 🦋💖