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'

Stanislav Fomichev committed 4 years ago

Commit 2172fb81 parent 8a67f2d2 files · +34 −10Browse files

Showing the changes to tools/include/uapi/linux (1 of 2 files). Show all

Unified · Split

tools/include/uapi/linux/bpf.h+17−5

@@ -5085,17 +5085,29 @@ union bpf_attr { · 5084 unmodified lines
5085	5085	*
5086	5086	* int bpf_get_retval(void)
5087	5087	* Description
5088		− * Get the syscall's return value that will be returned to userspace.
	5088	+ * Get the BPF program's return value that will be returned to the upper layers.
5089	5089	*
5090		− * This helper is currently supported by cgroup programs only.
	5090	+ * This helper is currently supported by cgroup programs and only by the hooks
	5091	+ * where BPF program's return value is returned to the userspace via errno.
5091	5092	* Return
5092		− * The syscall's return value.
	5093	+ * The BPF program's return value.
5093	5094	*
5094	5095	* int bpf_set_retval(int retval)
5095	5096	* Description
5096		− * Set the syscall's return value that will be returned to userspace.
	5097	+ * Set the BPF program's return value that will be returned to the upper layers.
	5098	+ *
	5099	+ * This helper is currently supported by cgroup programs and only by the hooks
	5100	+ * where BPF program's return value is returned to the userspace via errno.
	5101	+ *
	5102	+ * Note that there is the following corner case where the program exports an error
	5103	+ * via bpf_set_retval but signals success via 'return 1':
	5104	+ *
	5105	+ * bpf_set_retval(-EPERM);
	5106	+ * return 1;
	5107	+ *
	5108	+ * In this case, the BPF program's return value will use helper's -EPERM. This
	5109	+ * still holds true for cgroup/bind{4,6} which supports extra 'return 3' success case.
5097	5110	*
5098		− * This helper is currently supported by cgroup programs only.
5099	5111	* Return
5100	5112	* 0 on success, or a negative error in case of failure.
5101	5113	*