libbpf: Print hint about ulimit when getting permission denied error (dc3a2d25) · Commits · 戴 / test

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 -l' 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 -l' 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@redhat.com> Signed-off-by:

Alexei Starovoitov <ast@kernel.org> Acked-by:

Jesper Dangaard Brouer <brouer@redhat.com> Acked-by:

Yonghong Song <yhs@fb.com> Link: https://lore.kernel.org/bpf/20191216181204.724953-1-toke@redhat.com

tools/lib/bpf/libbpf.c

+29 −0

Original line number	Diff line number	Diff line
		@@ -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 +101,32 @@ void libbpf_print(enum libbpf_print_level level, const char *format, ...)
		va_end(args);
		}

		static void pr_perm_msg(int err)
		{
		struct rlimit limit;
		char buf[100];

		if (err != -EPERM \|\| geteuid() != 0)
		return;

		err = getrlimit(RLIMIT_MEMLOCK, &limit);
		if (err)
		return;

		if (limit.rlim_cur == RLIM_INFINITY)
		return;

		if (limit.rlim_cur < 1024)
		snprintf(buf, sizeof(buf), "%lu bytes", limit.rlim_cur);
		else if (limit.rlim_cur < 1024*1024)
		snprintf(buf, sizeof(buf), "%.1f KiB", (double)limit.rlim_cur / 1024);
		else
		snprintf(buf, sizeof(buf), "%.1f MiB", (double)limit.rlim_cur / (1024*1024));

		pr_warn("permission error while running as root; try raising 'ulimit -l'? current value: %s\n",
		buf);
		}

		#define STRERR_BUFSIZE 128

		/* Copied from tools/perf/util/util.h */
		@@ -2983,6 +3010,7 @@ err_out:
		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 +4409,7 @@ retry_load:
		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;

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