| Message ID | 20171211193903.2428317-2-yhs@fb.com |
|---|---|
| State | Accepted, archived |
| Delegated to: | BPF Maintainers |
| Headers | show |
| Series | bpf/tracing: allow user space to query prog array on the same tp | expand |
On Mon, Dec 11, 2017 at 11:39:02AM -0800, Yonghong Song wrote: > Commit e87c6bc3852b ("bpf: permit multiple bpf attachments > for a single perf event") added support to attach multiple > bpf programs to a single perf event. > Although this provides flexibility, users may want to know > what other bpf programs attached to the same tp interface. > Besides getting visibility for the underlying bpf system, > such information may also help consolidate multiple bpf programs, > understand potential performance issues due to a large array, > and debug (e.g., one bpf program which overwrites return code > may impact subsequent program results). > > Commit 2541517c32be ("tracing, perf: Implement BPF programs > attached to kprobes") utilized the existing perf ioctl > interface and added the command PERF_EVENT_IOC_SET_BPF > to attach a bpf program to a tracepoint. This patch adds a new > ioctl command, given a perf event fd, to query the bpf program > array attached to the same perf tracepoint event. > > The new uapi ioctl command: > PERF_EVENT_IOC_QUERY_BPF > > The new uapi/linux/perf_event.h structure: > struct perf_event_query_bpf { > __u32 ids_len; > __u32 prog_cnt; > __u32 ids[0]; > }; > > User space provides buffer "ids" for kernel to copy to. > When returning from the kernel, the number of available > programs in the array is set in "prog_cnt". > > The usage: > struct perf_event_query_bpf *query = malloc(...); > query.ids_len = ids_len; > err = ioctl(pmu_efd, PERF_EVENT_IOC_QUERY_BPF, &query); > if (err == 0) { > /* query.prog_cnt is the number of available progs, > * number of progs in ids: (ids_len == 0) ? 0 : query.prog_cnt > */ > } else if (errno == ENOSPC) { > /* query.ids_len number of progs copied, > * query.prog_cnt is the number of available progs > */ > } else { > /* other errors */ > } > > Signed-off-by: Yonghong Song <yhs@fb.com> > Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Alexei Starovoitov <ast@kernel.org>
On Mon, Dec 11, 2017 at 11:39:02AM -0800, Yonghong Song wrote: > The usage: > struct perf_event_query_bpf *query = malloc(...); > query.ids_len = ids_len; > err = ioctl(pmu_efd, PERF_EVENT_IOC_QUERY_BPF, &query); You didn't spot the fixes to your changelog ;-) The above should read something like: struct perf_event_query_bpf *query = malloc(sizeof(*query) + sizeof(u32) * ids_len); query->ids_len = ids_len; err = ioctl(pmu_efd, PERF_EVENT_IOC_QUERY_BPF, query);
On 12/12/17 1:03 AM, Peter Zijlstra wrote: > On Mon, Dec 11, 2017 at 11:39:02AM -0800, Yonghong Song wrote: >> The usage: >> struct perf_event_query_bpf *query = malloc(...); >> query.ids_len = ids_len; >> err = ioctl(pmu_efd, PERF_EVENT_IOC_QUERY_BPF, &query); > > You didn't spot the fixes to your changelog ;-) The above should read > something like: > > struct perf_event_query_bpf *query = > malloc(sizeof(*query) + sizeof(u32) * ids_len); > query->ids_len = ids_len; > err = ioctl(pmu_efd, PERF_EVENT_IOC_QUERY_BPF, query); sure. I fixed up this nit in commit log of patch 1 and in test_progs.c of patch 2.
diff --git a/include/linux/bpf.h b/include/linux/bpf.h index e55e425..f812ac5 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -254,6 +254,7 @@ typedef unsigned long (*bpf_ctx_copy_t)(void *dst, const void *src, u64 bpf_event_output(struct bpf_map *map, u64 flags, void *meta, u64 meta_size, void *ctx, u64 ctx_size, bpf_ctx_copy_t ctx_copy); +int bpf_event_query_prog_array(struct perf_event *event, void __user *info); int bpf_prog_test_run_xdp(struct bpf_prog *prog, const union bpf_attr *kattr, union bpf_attr __user *uattr); @@ -285,6 +286,9 @@ int bpf_prog_array_copy_to_user(struct bpf_prog_array __rcu *progs, void bpf_prog_array_delete_safe(struct bpf_prog_array __rcu *progs, struct bpf_prog *old_prog); +int bpf_prog_array_copy_info(struct bpf_prog_array __rcu *array, + __u32 __user *prog_ids, u32 request_cnt, + __u32 __user *prog_cnt); int bpf_prog_array_copy(struct bpf_prog_array __rcu *old_array, struct bpf_prog *exclude_prog, struct bpf_prog *include_prog, diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h index b9a4953..7695336 100644 --- a/include/uapi/linux/perf_event.h +++ b/include/uapi/linux/perf_event.h @@ -418,6 +418,27 @@ struct perf_event_attr { __u16 __reserved_2; /* align to __u64 */ }; +/* + * Structure used by below PERF_EVENT_IOC_QUERY_BPF command + * to query bpf programs attached to the same perf tracepoint + * as the given perf event. + */ +struct perf_event_query_bpf { + /* + * The below ids array length + */ + __u32 ids_len; + /* + * Set by the kernel to indicate the number of + * available programs + */ + __u32 prog_cnt; + /* + * User provided buffer to store program ids + */ + __u32 ids[0]; +}; + #define perf_flags(attr) (*(&(attr)->read_format + 1)) /* @@ -433,6 +454,7 @@ struct perf_event_attr { #define PERF_EVENT_IOC_ID _IOR('$', 7, __u64 *) #define PERF_EVENT_IOC_SET_BPF _IOW('$', 8, __u32) #define PERF_EVENT_IOC_PAUSE_OUTPUT _IOW('$', 9, __u32) +#define PERF_EVENT_IOC_QUERY_BPF _IOWR('$', 10, struct perf_event_query_bpf *) enum perf_event_ioc_flags { PERF_IOC_FLAG_GROUP = 1U << 0, diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c index 86b50aa..b16c6f8 100644 --- a/kernel/bpf/core.c +++ b/kernel/bpf/core.c @@ -1462,6 +1462,8 @@ int bpf_prog_array_copy_to_user(struct bpf_prog_array __rcu *progs, rcu_read_lock(); prog = rcu_dereference(progs)->progs; for (; *prog; prog++) { + if (*prog == &dummy_bpf_prog.prog) + continue; id = (*prog)->aux->id; if (copy_to_user(prog_ids + i, &id, sizeof(id))) { rcu_read_unlock(); @@ -1545,6 +1547,25 @@ int bpf_prog_array_copy(struct bpf_prog_array __rcu *old_array, return 0; } +int bpf_prog_array_copy_info(struct bpf_prog_array __rcu *array, + __u32 __user *prog_ids, u32 request_cnt, + __u32 __user *prog_cnt) +{ + u32 cnt = 0; + + if (array) + cnt = bpf_prog_array_length(array); + + if (copy_to_user(prog_cnt, &cnt, sizeof(cnt))) + return -EFAULT; + + /* return early if user requested only program count or nothing to copy */ + if (!request_cnt || !cnt) + return 0; + + return bpf_prog_array_copy_to_user(array, prog_ids, request_cnt); +} + static void bpf_prog_free_deferred(struct work_struct *work) { struct bpf_prog_aux *aux; diff --git a/kernel/events/core.c b/kernel/events/core.c index 4df5b69..53c65fb 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -4723,6 +4723,9 @@ static long _perf_ioctl(struct perf_event *event, unsigned int cmd, unsigned lon rcu_read_unlock(); return 0; } + + case PERF_EVENT_IOC_QUERY_BPF: + return bpf_event_query_prog_array(event, (void __user *)arg); default: return -ENOTTY; } diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c index 0ce99c3..b143f2a 100644 --- a/kernel/trace/bpf_trace.c +++ b/kernel/trace/bpf_trace.c @@ -820,3 +820,26 @@ void perf_event_detach_bpf_prog(struct perf_event *event) unlock: mutex_unlock(&bpf_event_mutex); } + +int bpf_event_query_prog_array(struct perf_event *event, void __user *info) +{ + struct perf_event_query_bpf __user *uquery = info; + struct perf_event_query_bpf query = {}; + int ret; + + if (!capable(CAP_SYS_ADMIN)) + return -EPERM; + if (event->attr.type != PERF_TYPE_TRACEPOINT) + return -EINVAL; + if (copy_from_user(&query, uquery, sizeof(query))) + return -EFAULT; + + mutex_lock(&bpf_event_mutex); + ret = bpf_prog_array_copy_info(event->tp_event->prog_array, + uquery->ids, + query.ids_len, + &uquery->prog_cnt); + mutex_unlock(&bpf_event_mutex); + + return ret; +}
Commit e87c6bc3852b ("bpf: permit multiple bpf attachments for a single perf event") added support to attach multiple bpf programs to a single perf event. Although this provides flexibility, users may want to know what other bpf programs attached to the same tp interface. Besides getting visibility for the underlying bpf system, such information may also help consolidate multiple bpf programs, understand potential performance issues due to a large array, and debug (e.g., one bpf program which overwrites return code may impact subsequent program results). Commit 2541517c32be ("tracing, perf: Implement BPF programs attached to kprobes") utilized the existing perf ioctl interface and added the command PERF_EVENT_IOC_SET_BPF to attach a bpf program to a tracepoint. This patch adds a new ioctl command, given a perf event fd, to query the bpf program array attached to the same perf tracepoint event. The new uapi ioctl command: PERF_EVENT_IOC_QUERY_BPF The new uapi/linux/perf_event.h structure: struct perf_event_query_bpf { __u32 ids_len; __u32 prog_cnt; __u32 ids[0]; }; User space provides buffer "ids" for kernel to copy to. When returning from the kernel, the number of available programs in the array is set in "prog_cnt". The usage: struct perf_event_query_bpf *query = malloc(...); query.ids_len = ids_len; err = ioctl(pmu_efd, PERF_EVENT_IOC_QUERY_BPF, &query); if (err == 0) { /* query.prog_cnt is the number of available progs, * number of progs in ids: (ids_len == 0) ? 0 : query.prog_cnt */ } else if (errno == ENOSPC) { /* query.ids_len number of progs copied, * query.prog_cnt is the number of available progs */ } else { /* other errors */ } Signed-off-by: Yonghong Song <yhs@fb.com> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> --- include/linux/bpf.h | 4 ++++ include/uapi/linux/perf_event.h | 22 ++++++++++++++++++++++ kernel/bpf/core.c | 21 +++++++++++++++++++++ kernel/events/core.c | 3 +++ kernel/trace/bpf_trace.c | 23 +++++++++++++++++++++++ 5 files changed, 73 insertions(+)