Merge branch 'bpf-batch-ops'

Merge branch 'bpf-batch-ops'

Brian Vazquez says:

====================
This patch series introduce batch ops that can be added to bpf maps to
lookup/lookup_and_delete/update/delete more than 1 element at the time,
this is specially useful when syscall overhead is a problem and in case
of hmap it will provide a reliable way of traversing them.

The implementation inclues a generic approach that could potentially be
used by any bpf map and adds it to arraymap, it also includes the specific
implementation of hashmaps which are traversed using buckets instead
of keys.

The bpf syscall subcommands introduced are:

  BPF_MAP_LOOKUP_BATCH
  BPF_MAP_LOOKUP_AND_DELETE_BATCH
  BPF_MAP_UPDATE_BATCH
  BPF_MAP_DELETE_BATCH

The UAPI attribute is:

  struct { /* struct used by BPF_MAP_*_BATCH commands */
         __aligned_u64   in_batch;       /* start batch,
                                          * NULL to start from beginning
                                          */
         __aligned_u64   out_batch;      /* output: next start batch */
         __aligned_u64   keys;
         __aligned_u64   values;
         __u32           count;          /* input/output:
                                          * input: # of key/value
                                          * elements
                                          * output: # of filled elements
                                          */
         __u32           map_fd;
         __u64           elem_flags;
         __u64           flags;
  } batch;

in_batch and out_batch are only used for lookup and lookup_and_delete since
those are the only two operations that attempt to traverse the map.

update/delete batch ops should provide the keys/values that user wants
to modify.

Here are the previous discussions on the batch processing:
 - https://lore.kernel.org/bpf/20190724165803.87470-1-brianvv@google.com/
 - https://lore.kernel.org/bpf/20190829064502.2750303-1-yhs@fb.com/
 - https://lore.kernel.org/bpf/20190906225434.3635421-1-yhs@fb.com/

Changelog sinve v4:
 - Remove unnecessary checks from libbpf API (Andrii Nakryiko)
 - Move DECLARE_LIBBPF_OPTS with all var declarations (Andrii Nakryiko)
 - Change bucket internal buffer size to 5 entries (Yonghong Song)
 - Fix some minor bugs in hashtab batch ops implementation (Yonghong Song)

Changelog sinve v3:
 - Do not use copy_to_user inside atomic region (Yonghong Song)
 - Use _opts approach on libbpf APIs (Andrii Nakryiko)
 - Drop generic_map_lookup_and_delete_batch support
 - Free malloc-ed memory in tests (Yonghong Song)
 - Reverse christmas tree (Yonghong Song)
 - Add acked labels

Changelog sinve v2:
 - Add generic batch support for lpm_trie and test it (Yonghong Song)
 - Use define MAP_LOOKUP_RETRIES for retries (John Fastabend)
 - Return errors directly and remove labels (Yonghong Song)
 - Insert new API functions into libbpf alphabetically (Yonghong Song)
 - Change hlist_nulls_for_each_entry_rcu to
   hlist_nulls_for_each_entry_safe in htab batch ops (Yonghong Song)

Changelog since v1:
 - Fix SOB ordering and remove Co-authored-by tag (Alexei Starovoitov)

Changelog since RFC:
 - Change batch to in_batch and out_batch to support more flexible opaque
   values to iterate the bpf maps.
 - Remove update/delete specific batch ops for htab and use the generic
   implementations instead.
====================

Acked-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>