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libbpf: ringbuf: Allow to consume up to a certain amount of items

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In some cases, instead of always consuming all items from ring buffers
in a greedy way, we may want to consume up to a certain amount of items,
for example when we need to copy items from the BPF ring buffer to a
limited user buffer.

This change allows to set an upper limit to the amount of items consumed
from one or more ring buffers.

Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20240406092005.92399-3-andrea.righi@canonical.com
This commit is contained in:
Andrea Righi
2024-04-06 11:15:42 +02:00
committed by Andrii Nakryiko
parent 26d9ab5f78
commit 98de9ace4d
1 changed files with 12 additions and 7 deletions
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19
src/ringbuf.c
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@@ -231,7 +231,7 @@ static inline int roundup_len(__u32 len)
return (len + 7) / 8 * 8; return (len + 7) / 8 * 8;
} }
static int64_t ringbuf_process_ring(struct ring *r) static int64_t ringbuf_process_ring(struct ring *r, size_t n)
{ {
int *len_ptr, len, err; int *len_ptr, len, err;
/* 64-bit to avoid overflow in case of extreme application behavior */ /* 64-bit to avoid overflow in case of extreme application behavior */
@@ -268,6 +268,9 @@ static int64_t ringbuf_process_ring(struct ring *r)
} }
smp_store_release(r->consumer_pos, cons_pos); smp_store_release(r->consumer_pos, cons_pos);
if (cnt >= n)
goto done;
} }
} while (got_new_data); } while (got_new_data);
done: done:
@@ -287,13 +290,15 @@ int ring_buffer__consume(struct ring_buffer *rb)
for (i = 0; i < rb->ring_cnt; i++) { for (i = 0; i < rb->ring_cnt; i++) {
struct ring *ring = rb->rings[i]; struct ring *ring = rb->rings[i];
err = ringbuf_process_ring(ring); err = ringbuf_process_ring(ring, INT_MAX);
if (err < 0) if (err < 0)
return libbpf_err(err); return libbpf_err(err);
res += err; res += err;
if (res > INT_MAX) {
res = INT_MAX;
break;
}
} }
if (res > INT_MAX)
return INT_MAX;
return res; return res;
} }
@@ -314,13 +319,13 @@ int ring_buffer__poll(struct ring_buffer *rb, int timeout_ms)
__u32 ring_id = rb->events[i].data.fd; __u32 ring_id = rb->events[i].data.fd;
struct ring *ring = rb->rings[ring_id]; struct ring *ring = rb->rings[ring_id];
err = ringbuf_process_ring(ring); err = ringbuf_process_ring(ring, INT_MAX);
if (err < 0) if (err < 0)
return libbpf_err(err); return libbpf_err(err);
res += err; res += err;
} }
if (res > INT_MAX) if (res > INT_MAX)
return INT_MAX; res = INT_MAX;
return res; return res;
} }
@@ -375,7 +380,7 @@ int ring__consume(struct ring *r)
{ {
int64_t res; int64_t res;
res = ringbuf_process_ring(r); res = ringbuf_process_ring(r, INT_MAX);
if (res < 0) if (res < 0)
return libbpf_err(res); return libbpf_err(res);