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Message-ID: <7008d545-ac78-3e22-aeaa-1d6639611225@fb.com>
Date: Mon, 11 May 2020 13:43:03 -0700
From: Yonghong Song <yhs@...com>
To: Eelco Chaudron <echaudro@...hat.com>, <bpf@...r.kernel.org>
CC: <davem@...emloft.net>, <netdev@...r.kernel.org>, <ast@...nel.org>,
<daniel@...earbox.net>, <kafai@...com>, <songliubraving@...com>,
<andriin@...com>, <toke@...hat.com>
Subject: Re: [PATCH bpf-next v3] libbpf: fix probe code to return EPERM if
encountered
On 5/11/20 5:40 AM, Eelco Chaudron wrote:
> When the probe code was failing for any reason ENOTSUP was returned, even
> if this was due to no having enough lock space. This patch fixes this by
> returning EPERM to the user application, so it can respond and increase
> the RLIMIT_MEMLOCK size.
>
> Signed-off-by: Eelco Chaudron <echaudro@...hat.com>
> ---
> v3: Updated error message to be more specific as suggested by Andrii
> v2: Split bpf_object__probe_name() in two functions as suggested by Andrii
>
> tools/lib/bpf/libbpf.c | 31 ++++++++++++++++++++++++++-----
> 1 file changed, 26 insertions(+), 5 deletions(-)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 8f480e29a6b0..ad3043c5db13 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -3149,7 +3149,7 @@ int bpf_map__resize(struct bpf_map *map, __u32 max_entries)
> }
>
> static int
> -bpf_object__probe_name(struct bpf_object *obj)
> +bpf_object__probe_loading(struct bpf_object *obj)
> {
> struct bpf_load_program_attr attr;
> char *cp, errmsg[STRERR_BUFSIZE];
> @@ -3170,14 +3170,34 @@ bpf_object__probe_name(struct bpf_object *obj)
> ret = bpf_load_program_xattr(&attr, NULL, 0);
> if (ret < 0) {
> cp = libbpf_strerror_r(errno, errmsg, sizeof(errmsg));
> - pr_warn("Error in %s():%s(%d). Couldn't load basic 'r0 = 0' BPF program.\n",
> - __func__, cp, errno);
> + pr_warn("Error in %s():%s(%d). Couldn't load trivial BPF "
> + "program. Make sure your kernel supports BPF "
> + "(CONFIG_BPF_SYSCALL=y) and/or that RLIMIT_MEMLOCK is "
> + "set to big enough value.\n", __func__, cp, errno);
> return -errno;
Just curious. Did "errno" always survive pr_warn() here? pr_warn() may
call user supplied print function which it outside libbpf control.
Maybe should cache errno before calling pr_warn()?
> }
> close(ret);
>
> - /* now try the same program, but with the name */
> + return 0;
> +}
> +
> +static int
> +bpf_object__probe_name(struct bpf_object *obj)
> +{
> + struct bpf_load_program_attr attr;
> + struct bpf_insn insns[] = {
> + BPF_MOV64_IMM(BPF_REG_0, 0),
> + BPF_EXIT_INSN(),
> + };
> + int ret;
> +
> + /* make sure loading with name works */
>
> + memset(&attr, 0, sizeof(attr));
> + attr.prog_type = BPF_PROG_TYPE_SOCKET_FILTER;
> + attr.insns = insns;
> + attr.insns_cnt = ARRAY_SIZE(insns);
> + attr.license = "GPL";
> attr.name = "test";
> ret = bpf_load_program_xattr(&attr, NULL, 0);
> if (ret >= 0) {
> @@ -5386,7 +5406,8 @@ int bpf_object__load_xattr(struct bpf_object_load_attr *attr)
>
> obj->loaded = true;
>
> - err = bpf_object__probe_caps(obj);
> + err = bpf_object__probe_loading(obj);
> + err = err ? : bpf_object__probe_caps(obj);
> err = err ? : bpf_object__resolve_externs(obj, obj->kconfig);
> err = err ? : bpf_object__sanitize_and_load_btf(obj);
> err = err ? : bpf_object__sanitize_maps(obj);
>
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