From: =?UTF-8?q?Toke=20H=C3=B8iland-J=C3=B8rgensen?= <toke@redhat.com>
Date: Mon, 16 Dec 2019 19:12:04 +0100
Subject: libbpf: Print hint about ulimit when getting permission denied error
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Patch-mainline: v5.6-rc1
Git-commit: dc3a2d254782dea8e23a55f46129105ecfe787fb
References: bsc#1177028
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
Acked-by: Gary Lin <glin@suse.com>
---
tools/lib/bpf/libbpf.c | 29 +++++++++++++++++++++++++++++
1 file changed, 29 insertions(+)
--- 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 +101,32 @@ void libbpf_print(enum libbpf_print_leve
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_warning("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_warning("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;
@@ -4383,6 +4411,7 @@ retry_load:
ret = -errno;
cp = libbpf_strerror_r(errno, errmsg, sizeof(errmsg));
pr_warning("load bpf program failed: %s\n", cp);
+ pr_perm_msg(ret);
if (log_buf && log_buf[0] != '\0') {
ret = -LIBBPF_ERRNO__VERIFY;