[PATCH bpf-next 0/6] bpf: add BPF_MAP_DUMP command to dump more than one entry per call

From: Brian Vazquez
Date: Wed Jul 24 2019 - 12:58:22 EST

This introduces a new command to retrieve multiple number of entries
from a bpf map.

This new command can be executed from the existing BPF syscall as

err = bpf(BPF_MAP_DUMP, union bpf_attr *attr, u32 size)
using attr->dump.map_fd, attr->dump.prev_key, attr->dump.buf,
returns zero or negative error, and populates buf and buf_len on

This implementation is wrapping the existing bpf methods:
map_get_next_key and map_lookup_elem

Note that this implementation can be extended later to do dump and
delete by extending map_lookup_and_delete_elem (currently it only works
for bpf queue/stack maps) and either use a new flag in map_dump or a new
command map_dump_and_delete.

Results show that even with a 1-elem_size buffer, it runs ~40 faster
than the current implementation, improvements of ~85% are reported when
the buffer size is increased, although, after the buffer size is around
5% of the total number of entries there's no huge difference in
increasing it.

Tried different size buffers to handle case where the bulk is bigger, or
the elements to retrieve are less than the existing ones, all runs read
a map of 100K entries. Below are the results(in ns) from the different

buf_len_1: 69038725 entry-by-entry: 112384424 improvement
buf_len_2: 40897447 entry-by-entry: 111030546 improvement
buf_len_230: 13652714 entry-by-entry: 111694058 improvement
buf_len_5000: 13576271 entry-by-entry: 111101169 improvement
buf_len_73000: 14694343 entry-by-entry: 111740162 improvement
buf_len_100000: 13745969 entry-by-entry: 114151991 improvement
buf_len_234567: 14329834 entry-by-entry: 114427589 improvement

The series of patches are split as follows:

- First patch move some map_lookup_elem logic into 2 fucntions to
deduplicate code: bpf_map_value_size and bpf_map_copy_value
- Second patch introduce map_dump function
- Third patch syncs tools linux headers
- Fourth patch adds libbpf support
- Last two patches adds tests

RFC Changelog:

- remove wrong usage of attr.flags
- move map_fd to remove hole after it

- add explanation of the API in the commit message
- fix masked errors and return them to user
- copy last_key from return buf into prev_key if it was provided
- run perf test with kpti and retpoline mitigations

- use proper bpf-next tag

Brian Vazquez (6):
bpf: add bpf_map_value_size and bp_map_copy_value helper functions
bpf: add BPF_MAP_DUMP command to dump more than one entry per call
bpf: keep bpf.h in sync with tools/
libbpf: support BPF_MAP_DUMP command
selftests/bpf: test BPF_MAP_DUMP command on a bpf hashmap
selftests/bpf: add test to measure performance of BPF_MAP_DUMP

include/uapi/linux/bpf.h | 9 +
kernel/bpf/syscall.c | 251 ++++++++++++++++++------
tools/include/uapi/linux/bpf.h | 9 +
tools/lib/bpf/bpf.c | 28 +++
tools/lib/bpf/bpf.h | 4 +
tools/lib/bpf/libbpf.map | 2 +
tools/testing/selftests/bpf/test_maps.c | 148 +++++++++++++-
7 files changed, 388 insertions(+), 63 deletions(-)