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Date: Mon, 7 Oct 2019 20:25:19 +0900
From: "Daniel T. Lee" <danieltimlee@...il.com>
To: Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc: Yonghong Song <yhs@...com>, Song Liu <liu.song.a23@...il.com>,
Daniel Borkmann <daniel@...earbox.net>,
Alexei Starovoitov <ast@...nel.org>, bpf <bpf@...r.kernel.org>,
Networking <netdev@...r.kernel.org>
Subject: Re: [bpf-next v5] samples: bpf: add max_pckt_size option at xdp_adjust_tail
On Mon, Oct 7, 2019 at 12:37 PM Andrii Nakryiko
<andrii.nakryiko@...il.com> wrote:
>
> On Sun, Oct 6, 2019 at 4:58 AM Daniel T. Lee <danieltimlee@...il.com> wrote:
> >
> > Currently, at xdp_adjust_tail_kern.c, MAX_PCKT_SIZE is limited
> > to 600. To make this size flexible, static global variable
> > 'max_pcktsz' is added.
> >
> > By updating new packet size from the user space, xdp_adjust_tail_kern.o
> > will use this value as a new max packet size.
> >
> > This static global variable can be accesible from .data section with
> > bpf_object__find_map* from user space, since it is considered as
> > internal map (accessible with .bss/.data/.rodata suffix).
> >
> > If no '-P <MAX_PCKT_SIZE>' option is used, the size of maximum packet
> > will be 600 as a default.
> >
> > Changed the way to test prog_fd, map_fd from '!= 0' to '< 0',
> > since fd could be 0 when stdin is closed.
> >
> > Signed-off-by: Daniel T. Lee <danieltimlee@...il.com>
> >
> > ---
>
> See nit below, but otherwise looks good.
>
> Acked-by: Andrii Nakryiko <andriin@...com>
>
> > Changes in v5:
> > - Change pcktsz map to static global variable
> > Changes in v4:
> > - make pckt_size no less than ICMP_TOOBIG_SIZE
> > - Fix code style
> > Changes in v2:
> > - Change the helper to fetch map from 'bpf_map__next' to
> > 'bpf_object__find_map_fd_by_name'.
> >
> > samples/bpf/xdp_adjust_tail_kern.c | 7 +++++--
> > samples/bpf/xdp_adjust_tail_user.c | 32 ++++++++++++++++++++++--------
> > 2 files changed, 29 insertions(+), 10 deletions(-)
> >
> > diff --git a/samples/bpf/xdp_adjust_tail_kern.c b/samples/bpf/xdp_adjust_tail_kern.c
> > index 411fdb21f8bc..c616508befb9 100644
> > --- a/samples/bpf/xdp_adjust_tail_kern.c
> > +++ b/samples/bpf/xdp_adjust_tail_kern.c
> > @@ -25,6 +25,9 @@
> > #define ICMP_TOOBIG_SIZE 98
> > #define ICMP_TOOBIG_PAYLOAD_SIZE 92
> >
> > +/* volatile to prevent compiler optimizations */
> > +static volatile __u32 max_pcktsz = MAX_PCKT_SIZE;
> > +
> > struct bpf_map_def SEC("maps") icmpcnt = {
> > .type = BPF_MAP_TYPE_ARRAY,
> > .key_size = sizeof(__u32),
> > @@ -92,7 +95,7 @@ static __always_inline int send_icmp4_too_big(struct xdp_md *xdp)
> > orig_iph = data + off;
> > icmp_hdr->type = ICMP_DEST_UNREACH;
> > icmp_hdr->code = ICMP_FRAG_NEEDED;
> > - icmp_hdr->un.frag.mtu = htons(MAX_PCKT_SIZE-sizeof(struct ethhdr));
> > + icmp_hdr->un.frag.mtu = htons(max_pcktsz - sizeof(struct ethhdr));
> > icmp_hdr->checksum = 0;
> > ipv4_csum(icmp_hdr, ICMP_TOOBIG_PAYLOAD_SIZE, &csum);
> > icmp_hdr->checksum = csum;
> > @@ -121,7 +124,7 @@ static __always_inline int handle_ipv4(struct xdp_md *xdp)
> > int pckt_size = data_end - data;
> > int offset;
> >
> > - if (pckt_size > MAX_PCKT_SIZE) {
> > + if (pckt_size > max(max_pcktsz, ICMP_TOOBIG_SIZE)) {
> > offset = pckt_size - ICMP_TOOBIG_SIZE;
> > if (bpf_xdp_adjust_tail(xdp, 0 - offset))
> > return XDP_PASS;
> > diff --git a/samples/bpf/xdp_adjust_tail_user.c b/samples/bpf/xdp_adjust_tail_user.c
> > index a3596b617c4c..bcdebd3be83e 100644
> > --- a/samples/bpf/xdp_adjust_tail_user.c
> > +++ b/samples/bpf/xdp_adjust_tail_user.c
> > @@ -23,6 +23,7 @@
> > #include "libbpf.h"
> >
> > #define STATS_INTERVAL_S 2U
> > +#define MAX_PCKT_SIZE 600
> >
> > static int ifindex = -1;
> > static __u32 xdp_flags = XDP_FLAGS_UPDATE_IF_NOEXIST;
> > @@ -72,6 +73,7 @@ static void usage(const char *cmd)
> > printf("Usage: %s [...]\n", cmd);
> > printf(" -i <ifname|ifindex> Interface\n");
> > printf(" -T <stop-after-X-seconds> Default: 0 (forever)\n");
> > + printf(" -P <MAX_PCKT_SIZE> Default: %u\n", MAX_PCKT_SIZE);
> > printf(" -S use skb-mode\n");
> > printf(" -N enforce native mode\n");
> > printf(" -F force loading prog\n");
> > @@ -85,13 +87,14 @@ int main(int argc, char **argv)
> > .prog_type = BPF_PROG_TYPE_XDP,
> > };
> > unsigned char opt_flags[256] = {};
> > - const char *optstr = "i:T:SNFh";
> > + const char *optstr = "i:T:P:SNFh";
> > struct bpf_prog_info info = {};
> > __u32 info_len = sizeof(info);
> > unsigned int kill_after_s = 0;
> > int i, prog_fd, map_fd, opt;
> > struct bpf_object *obj;
> > - struct bpf_map *map;
> > + __u32 max_pckt_size = 0;
> > + __u32 key = 0;
> > char filename[256];
> > int err;
> >
> > @@ -110,6 +113,9 @@ int main(int argc, char **argv)
> > case 'T':
> > kill_after_s = atoi(optarg);
> > break;
> > + case 'P':
> > + max_pckt_size = atoi(optarg);
> > + break;
> > case 'S':
> > xdp_flags |= XDP_FLAGS_SKB_MODE;
> > break;
> > @@ -150,15 +156,25 @@ int main(int argc, char **argv)
> > if (bpf_prog_load_xattr(&prog_load_attr, &obj, &prog_fd))
> > return 1;
> >
> > - map = bpf_map__next(NULL, obj);
> > - if (!map) {
> > - printf("finding a map in obj file failed\n");
> > + if (prog_fd < 0) {
> > + printf("load_bpf_file: %s\n", strerror(errno));
>
> program load error is checked above (bpf_prog_load_xattr check), not
> clear why check this again... Maybe just print helpful message there?
>
Oh, It won't be necessary since it gets error from 'bpf_prog_load_xattr'.
I'll resend the patch with this nit fixed.
Thanks for the review!
Thanks,
Daniel
> > return 1;
> > }
> > - map_fd = bpf_map__fd(map);
> >
> > - if (!prog_fd) {
> > - printf("load_bpf_file: %s\n", strerror(errno));
> > + /* static global var 'max_pcktsz' is accessible from .data section */
> > + if (max_pckt_size) {
> > + map_fd = bpf_object__find_map_fd_by_name(obj, "xdp_adju.data");
> > + if (map_fd < 0) {
> > + printf("finding a max_pcktsz map in obj file failed\n");
> > + return 1;
> > + }
> > + bpf_map_update_elem(map_fd, &key, &max_pckt_size, BPF_ANY);
> > + }
> > +
> > + /* fetch icmpcnt map */
> > + map_fd = bpf_object__find_map_fd_by_name(obj, "icmpcnt");
> > + if (map_fd < 0) {
> > + printf("finding a icmpcnt map in obj file failed\n");
> > return 1;
> > }
> >
> > --
> > 2.20.1
> >
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