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libbpf: Print hint about ulimit when getting permission denied error

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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
This commit is contained in:
Toke Høiland-Jørgensen 2019-12-16 19:12:04 +01:00 committed by Alexei Starovoitov
parent d50ecc46d1
commit dc3a2d2547
1 changed files with 29 additions and 0 deletions
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29
tools/lib/bpf/libbpf.c
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@ -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;