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bpf: update bpf_{g,s}et_retval documentation

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* 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 <kafai@fb.com>
Signed-off-by: Stanislav Fomichev <sdf@google.com>
Link: https://lore.kernel.org/r/20220823222555.523590-5-sdf@google.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Stanislav Fomichev 2022-08-23 15:25:54 -07:00 committed by Alexei Starovoitov
parent 8a67f2de9b
commit 2172fb8007
2 changed files with 34 additions and 10 deletions
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22
include/uapi/linux/bpf.h
View File

@ -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.
*

22
tools/include/uapi/linux/bpf.h
View File

@ -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.
*