From 2172fb8007eaafbef18563afb6c1ae5a976bf787 Mon Sep 17 00:00:00 2001 From: Stanislav Fomichev Date: Tue, 23 Aug 2022 15:25:54 -0700 Subject: bpf: update bpf_{g,s}et_retval documentation * replace 'syscall' with 'upper layers', still mention that it's being exported via syscall errno * describe what happens in set_retval(-EPERM) + return 1 * describe what happens with bind's 'return 3' Acked-by: Martin KaFai Lau Signed-off-by: Stanislav Fomichev Link: https://lore.kernel.org/r/20220823222555.523590-5-sdf@google.com Signed-off-by: Alexei Starovoitov --- include/uapi/linux/bpf.h | 22 +++++++++++++++++----- 1 file changed, 17 insertions(+), 5 deletions(-) (limited to 'include/uapi/linux/bpf.h') diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h index 7f87012b012e..644600dbb114 100644 --- a/include/uapi/linux/bpf.h +++ b/include/uapi/linux/bpf.h @@ -5085,17 +5085,29 @@ union bpf_attr { * * int bpf_get_retval(void) * Description - * Get the syscall's return value that will be returned to userspace. + * Get the BPF program's return value that will be returned to the upper layers. * - * This helper is currently supported by cgroup programs only. + * This helper is currently supported by cgroup programs and only by the hooks + * where BPF program's return value is returned to the userspace via errno. * Return - * The syscall's return value. + * The BPF program's return value. * * int bpf_set_retval(int retval) * Description - * Set the syscall's return value that will be returned to userspace. + * Set the BPF program's return value that will be returned to the upper layers. + * + * This helper is currently supported by cgroup programs and only by the hooks + * where BPF program's return value is returned to the userspace via errno. + * + * Note that there is the following corner case where the program exports an error + * via bpf_set_retval but signals success via 'return 1': + * + * bpf_set_retval(-EPERM); + * return 1; + * + * In this case, the BPF program's return value will use helper's -EPERM. This + * still holds true for cgroup/bind{4,6} which supports extra 'return 3' success case. * - * This helper is currently supported by cgroup programs only. * Return * 0 on success, or a negative error in case of failure. * -- cgit v1.2.3