[RFC PATCH 10/11] bpf: add bpf_buffer_reserve and bpf_buffer_commit

Kris Van Hees
2019-05-21T20:41:08Z

Add two helpers that are primarily used in combination with the
writable-buffer support. The bpf_buffer_reserve() helper sets aside
a chunk of buffer space that can be written to, and once all data
has been written, the bpf_buffer_commit() helper is used to make the
data in the ring buffer visible to userspace.

Signed-off-by: Kris Van Hees <kris.van.hees@oracle.com>
Reviewed-by: Nick Alcock <nick.alcock@oracle.com>
---
include/uapi/linux/bpf.h | 39 ++++++++++++++++++++++-
kernel/bpf/verifier.c | 6 +++-
tools/include/uapi/linux/bpf.h | 39 ++++++++++++++++++++++-
tools/testing/selftests/bpf/bpf_helpers.h | 4 +++
4 files changed, 85 insertions(+), 3 deletions(-)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 7bcb707539d1..2b7772aa00b6 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -2681,6 +2681,41 @@ union bpf_attr {
* the implementing program type.
* Return
* 0 on success, or a negative error in case of failure.
+ *
+ * int bpf_buffer_reserve(void *ctx, int id, struct bpf_map *map, int size)
+ * Description
+ * Reserve *size* bytes in the output buffer for the special BPF
+ * BPF perf event referenced by *map*, a BPF map of type
+ * **BPF_MAP_TYPE_PERF_EVENT_ARRAY**. The perf event must have
+ * the attributes: **PERF_SAMPLE_RAW** as **sample_type**,
+ * **PERF_TYPE_SOFTWARE** as **type**, and
+ * **PERF_COUNT_SW_BPF_OUTPUT** as **config**. The reserved space
+ * will be available as the writable buffer identified with
+ * numeric ID **id** in the context.
+ *
+ * The amount of reserved bytes cannot exceed the page size.
+ * The chunk of buffer space will be reserved within a single
+ * page, and if this results in unused space at the end of the
+ * previous page in the ring-buffer, that unsused space will be
+ * filled with zeros.
+ * Return
+ * 0 on success, or a negative error in case of failure.
+ *
+ * int bpf_buffer_commit(void *ctx, int id, struct bpf_map *map)
+ * Description
+ * FInalize the previously reserved space in the output buffer
+ * for the special BPF perf event referenced by *map*, a BPF map
+ * of type **BPF_MAP_TYPE_PERF_EVENT_ARRAY**. The perf event must
+ * have the attributes: **PERF_SAMPLE_RAW** as **sample_type**,
+ * **PERF_TYPE_SOFTWARE** as **type**, and
+ * **PERF_COUNT_SW_BPF_OUTPUT** as **config**.
+ *
+ * The writable buffer identified with numeric ID **id** in the
+ * context will be invalidated, and can no longer be used to
+ * write data to until a new **bpf_buffer_reserve**\ () has been
+ * invoked.
+ * Return
+ * 0 on success, or a negative error in case of failure.
*/
#define __BPF_FUNC_MAPPER(FN) \
FN(unspec), \
@@ -2792,7 +2827,9 @@ union bpf_attr {
FN(strtoul), \
FN(sk_storage_get), \
FN(sk_storage_delete), \
- FN(finalize_context),
+ FN(finalize_context), \
+ FN(buffer_reserve), \
+ FN(buffer_commit),

/* integer value in 'imm' field of BPF_CALL instruction selects which helper
* function eBPF program intends to call
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 90ae04b4d5c7..ff73ed743a58 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -2763,7 +2763,9 @@ static int check_map_func_compatibility(struct bpf_verifier_env *env,
case BPF_MAP_TYPE_PERF_EVENT_ARRAY:
if (func_id != BPF_FUNC_perf_event_read &&
func_id != BPF_FUNC_perf_event_output &&
- func_id != BPF_FUNC_perf_event_read_value)
+ func_id != BPF_FUNC_perf_event_read_value &&
+ func_id != BPF_FUNC_buffer_reserve &&
+ func_id != BPF_FUNC_buffer_commit)
goto error;
break;
case BPF_MAP_TYPE_STACK_TRACE:
@@ -2848,6 +2850,8 @@ static int check_map_func_compatibility(struct bpf_verifier_env *env,
case BPF_FUNC_perf_event_read:
case BPF_FUNC_perf_event_output:
case BPF_FUNC_perf_event_read_value:
+ case BPF_FUNC_buffer_reserve:
+ case BPF_FUNC_buffer_commit:
if (map->map_type != BPF_MAP_TYPE_PERF_EVENT_ARRAY)
goto error;
break;
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 7bcb707539d1..2b7772aa00b6 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -2681,6 +2681,41 @@ union bpf_attr {
* the implementing program type.
* Return
* 0 on success, or a negative error in case of failure.
+ *
+ * int bpf_buffer_reserve(void *ctx, int id, struct bpf_map *map, int size)
+ * Description
+ * Reserve *size* bytes in the output buffer for the special BPF
+ * BPF perf event referenced by *map*, a BPF map of type
+ * **BPF_MAP_TYPE_PERF_EVENT_ARRAY**. The perf event must have
+ * the attributes: **PERF_SAMPLE_RAW** as **sample_type**,
+ * **PERF_TYPE_SOFTWARE** as **type**, and
+ * **PERF_COUNT_SW_BPF_OUTPUT** as **config**. The reserved space
+ * will be available as the writable buffer identified with
+ * numeric ID **id** in the context.
+ *
+ * The amount of reserved bytes cannot exceed the page size.
+ * The chunk of buffer space will be reserved within a single
+ * page, and if this results in unused space at the end of the
+ * previous page in the ring-buffer, that unsused space will be
+ * filled with zeros.
+ * Return
+ * 0 on success, or a negative error in case of failure.
+ *
+ * int bpf_buffer_commit(void *ctx, int id, struct bpf_map *map)
+ * Description
+ * FInalize the previously reserved space in the output buffer
+ * for the special BPF perf event referenced by *map*, a BPF map
+ * of type **BPF_MAP_TYPE_PERF_EVENT_ARRAY**. The perf event must
+ * have the attributes: **PERF_SAMPLE_RAW** as **sample_type**,
+ * **PERF_TYPE_SOFTWARE** as **type**, and
+ * **PERF_COUNT_SW_BPF_OUTPUT** as **config**.
+ *
+ * The writable buffer identified with numeric ID **id** in the
+ * context will be invalidated, and can no longer be used to
+ * write data to until a new **bpf_buffer_reserve**\ () has been
+ * invoked.
+ * Return
+ * 0 on success, or a negative error in case of failure.
*/
#define __BPF_FUNC_MAPPER(FN) \
FN(unspec), \
@@ -2792,7 +2827,9 @@ union bpf_attr {
FN(strtoul), \
FN(sk_storage_get), \
FN(sk_storage_delete), \
- FN(finalize_context),
+ FN(finalize_context), \
+ FN(buffer_reserve), \
+ FN(buffer_commit),

/* integer value in 'imm' field of BPF_CALL instruction selects which helper
* function eBPF program intends to call
diff --git a/tools/testing/selftests/bpf/bpf_helpers.h b/tools/testing/selftests/bpf/bpf_helpers.h
index d98a62b3b56c..72af8157d4db 100644
--- a/tools/testing/selftests/bpf/bpf_helpers.h
+++ b/tools/testing/selftests/bpf/bpf_helpers.h
@@ -218,6 +218,10 @@ static int (*bpf_sk_storage_delete)(void *map, struct bpf_sock *sk) =
(void *)BPF_FUNC_sk_storage_delete;
static int (*bpf_finalize_context)(void *ctx, void *map) =
(void *) BPF_FUNC_finalize_context;
+static int (*bpf_buffer_reserve)(void *ctx, int id, void *map, int size) =
+ (void *) BPF_FUNC_buffer_reserve;
+static int (*bpf_buffer_commit)(void *ctx, int id, void *map) =
+ (void *) BPF_FUNC_buffer_commit;

/* llvm builtin functions that eBPF C program may use to
* emit BPF_LD_ABS and BPF_LD_IND instructions
--
2.20.1