diff options
| author | Namhyung Kim <namhyung@kernel.org> | 2022-03-14 21:20:41 +0300 |
|---|---|---|
| committer | Alexei Starovoitov <ast@kernel.org> | 2022-03-21 05:16:23 +0300 |
| commit | ee2a098851bfbe8bcdd964c0121f4246f00ff41e (patch) | |
| tree | fb340d9c13b9ed24ef2b964a6c48149fab365467 /include/uapi/linux/bpf.h | |
| parent | ef078600eec20f20eb7833cf597d4a5edf2953c1 (diff) | |
| download | linux-ee2a098851bfbe8bcdd964c0121f4246f00ff41e.tar.xz | |
bpf: Adjust BPF stack helper functions to accommodate skip > 0
Let's say that the caller has storage for num_elem stack frames. Then,
the BPF stack helper functions walk the stack for only num_elem frames.
This means that if skip > 0, one keeps only 'num_elem - skip' frames.
This is because it sets init_nr in the perf_callchain_entry to the end
of the buffer to save num_elem entries only. I believe it was because
the perf callchain code unwound the stack frames until it reached the
global max size (sysctl_perf_event_max_stack).
However it now has perf_callchain_entry_ctx.max_stack to limit the
iteration locally. This simplifies the code to handle init_nr in the
BPF callstack entries and removes the confusion with the perf_event's
__PERF_SAMPLE_CALLCHAIN_EARLY which sets init_nr to 0.
Also change the comment on bpf_get_stack() in the header file to be
more explicit what the return value means.
Fixes: c195651e565a ("bpf: add bpf_get_stack helper")
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/30a7b5d5-6726-1cc2-eaee-8da2828a9a9c@oracle.com
Link: https://lore.kernel.org/bpf/20220314182042.71025-1-namhyung@kernel.org
Based-on-patch-by: Eugene Loh <eugene.loh@oracle.com>
Diffstat (limited to 'include/uapi/linux/bpf.h')
| -rw-r--r-- | include/uapi/linux/bpf.h | 8 |
1 files changed, 4 insertions, 4 deletions
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h index 7604e7d5438f..d14b10b85e51 100644 --- a/include/uapi/linux/bpf.h +++ b/include/uapi/linux/bpf.h @@ -3009,8 +3009,8 @@ union bpf_attr { * * # sysctl kernel.perf_event_max_stack=<new value> * Return - * A non-negative value equal to or less than *size* on success, - * or a negative error in case of failure. + * The non-negative copied *buf* length equal to or less than + * *size* on success, or a negative error in case of failure. * * long bpf_skb_load_bytes_relative(const void *skb, u32 offset, void *to, u32 len, u32 start_header) * Description @@ -4316,8 +4316,8 @@ union bpf_attr { * * # sysctl kernel.perf_event_max_stack=<new value> * Return - * A non-negative value equal to or less than *size* on success, - * or a negative error in case of failure. + * The non-negative copied *buf* length equal to or less than + * *size* on success, or a negative error in case of failure. * * long bpf_load_hdr_opt(struct bpf_sock_ops *skops, void *searchby_res, u32 len, u64 flags) * Description |