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AF_XDP-interaction: Explain xsk_btf__read_field in user code

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Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
This commit is contained in:
Jesper Dangaard Brouer
2021-11-11 14:34:43 +01:00
parent a333281166
commit 8703e1a320
1 changed files with 9 additions and 4 deletions
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13
AF_XDP-interaction/af_xdp_user.c
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@@ -399,7 +399,8 @@ static void print_meta_info_mark(uint8_t *pkt, struct xdp_hints_mark *meta)
printf("meta-mark mark:%u\n", mark); printf("meta-mark mark:%u\n", mark);
} }
static int print_meta_info_time(uint8_t *pkt) /* Demo API xsk_btf__read_field() that use string for BTF lookup */
static int print_meta_info_time_api2(uint8_t *pkt)
{ {
struct xsk_btf_info *xbi = xdp_hints_rx_time.xbi; struct xsk_btf_info *xbi = xdp_hints_rx_time.xbi;
__u64 time_now; // = gettime(); __u64 time_now; // = gettime();
@@ -408,7 +409,10 @@ static int print_meta_info_time(uint8_t *pkt)
__u64 diff; __u64 diff;
int err; int err;
/* Notice how rx_ktime_ptr becomes a pointer into struct memory */ /* This API cache string lookup (in hashmap), which cause an
* allocation first time this is called. Something to consider
* for real-time use-cases.
*/
err = xsk_btf__read_field((void **)&rx_ktime_ptr, sizeof(*rx_ktime_ptr), err = xsk_btf__read_field((void **)&rx_ktime_ptr, sizeof(*rx_ktime_ptr),
"rx_ktime", xbi, pkt); "rx_ktime", xbi, pkt);
if (err) { if (err) {
@@ -428,7 +432,7 @@ static int print_meta_info_time(uint8_t *pkt)
return 0; return 0;
} }
static int print_meta_info_time_faster(uint8_t *pkt, struct xdp_hints_rx_time *meta) static int print_meta_info_time(uint8_t *pkt, struct xdp_hints_rx_time *meta)
{ {
__u64 time_now; // = gettime(); __u64 time_now; // = gettime();
__u64 *rx_ktime_ptr; /* Points directly to member memory */ __u64 *rx_ktime_ptr; /* Points directly to member memory */
@@ -436,13 +440,14 @@ static int print_meta_info_time_faster(uint8_t *pkt, struct xdp_hints_rx_time *m
__u64 diff; __u64 diff;
int err; int err;
/* Use API that doesn't involve allocations to access BTF struct member */ /* API doesn't involve allocations to access BTF struct member */
err = xsk_btf__read((void **)&rx_ktime_ptr, sizeof(*rx_ktime_ptr), err = xsk_btf__read((void **)&rx_ktime_ptr, sizeof(*rx_ktime_ptr),
&meta->rx_ktime, meta->xbi, pkt); &meta->rx_ktime, meta->xbi, pkt);
if (err) { if (err) {
fprintf(stderr, "ERROR(%d) no rx_ktime?!\n", err); fprintf(stderr, "ERROR(%d) no rx_ktime?!\n", err);
return err; return err;
} }
/* Notice how rx_ktime_ptr becomes a pointer into struct memory */
rx_ktime = *rx_ktime_ptr; rx_ktime = *rx_ktime_ptr;
time_now = gettime(); time_now = gettime();