Probably the single most common error newcomers to XDP are stumped by is the 'permission denied' error they get when trying to load their program and 'ulimit -r' is set too low. For examples, see [0], [1]. Since the error code is UAPI, we can't change that. Instead, this patch adds a few heuristics in libbpf and outputs an additional hint if they are met: If an EPERM is returned on map create or program load, and geteuid() shows we are root, and the current RLIMIT_MEMLOCK is not infinity, we output a hint about raising 'ulimit -r' as an additional log line. [0] https://marc.info/?l=xdp-newbies&m=157043612505624&w=2 [1] https://github.com/xdp-project/xdp-tutorial/issues/86 Signed-off-by: Toke Høiland-Jørgensen <toke@xxxxxxxxxx> --- tools/lib/bpf/libbpf.c | 21 +++++++++++++++++++++ 1 file changed, 21 insertions(+) diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c index a2cc7313763a..aec7995674d2 100644 --- a/tools/lib/bpf/libbpf.c +++ b/tools/lib/bpf/libbpf.c @@ -41,6 +41,7 @@ #include <sys/types.h> #include <sys/vfs.h> #include <sys/utsname.h> +#include <sys/resource.h> #include <tools/libc_compat.h> #include <libelf.h> #include <gelf.h> @@ -100,6 +101,24 @@ void libbpf_print(enum libbpf_print_level level, const char *format, ...) va_end(args); } +static void pr_perm_msg(int err) +{ + struct rlimit limit; + + if (err != -EPERM || geteuid() != 0) + return; + + err = getrlimit(RLIMIT_MEMLOCK, &limit); + if (err) + return; + + if (limit.rlim_cur == RLIM_INFINITY) + return; + + pr_warn("permission error while running as root; try raising 'ulimit -r'? current value: %lu\n", + limit.rlim_cur); +} + #define STRERR_BUFSIZE 128 /* Copied from tools/perf/util/util.h */ @@ -2983,6 +3002,7 @@ bpf_object__create_maps(struct bpf_object *obj) cp = libbpf_strerror_r(err, errmsg, sizeof(errmsg)); pr_warn("failed to create map (name: '%s'): %s(%d)\n", map->name, cp, err); + pr_perm_msg(err); for (j = 0; j < i; j++) zclose(obj->maps[j].fd); return err; @@ -4381,6 +4401,7 @@ load_program(struct bpf_program *prog, struct bpf_insn *insns, int insns_cnt, ret = -errno; cp = libbpf_strerror_r(errno, errmsg, sizeof(errmsg)); pr_warn("load bpf program failed: %s\n", cp); + pr_perm_msg(ret); if (log_buf && log_buf[0] != '\0') { ret = -LIBBPF_ERRNO__VERIFY; -- 2.24.0
