bpf: Remove btf_field_offs, use btf_record's fields instead

The btf_field_offs struct contains (offset, size) for btf_record fields,
sorted by offset. btf_field_offs is always used in conjunction with
btf_record, which has btf_field 'fields' array with (offset, type), the
latter of which btf_field_offs' size is derived from via
btf_field_type_size.

This patch adds a size field to struct btf_field and sorts btf_record's
fields by offset, making it possible to get rid of btf_field_offs. Less
data duplication and less code complexity results.

Since btf_field_offs' lifetime closely followed the btf_record used to
populate it, most complexity wins are from removal of initialization
code like:

  if (btf_record_successfully_initialized) {
    foffs = btf_parse_field_offs(rec);
    if (IS_ERR_OR_NULL(foffs))
      // free the btf_record and return err
  }

Other changes in this patch are pretty mechanical:

  * foffs->field_off[i] -> rec->fields[i].offset
  * foffs->field_sz[i] -> rec->fields[i].size
  * Sort rec->fields in btf_parse_fields before returning
    * It's possible that this is necessary independently of other
      changes in this patch. btf_record_find in syscall.c expects
      btf_record's fields to be sorted by offset, yet there's no
      explicit sorting of them before this patch, record's fields are
      populated in the order they're read from BTF struct definition.
      BTF docs don't say anything about the sortedness of struct fields.
  * All functions taking struct btf_field_offs * input now instead take
    struct btf_record *. All callsites of these functions already have
    access to the correct btf_record.

Signed-off-by: Dave Marchevsky <davemarchevsky@fb.com>
Link: https://lore.kernel.org/r/20230415201811.343116-2-davemarchevsky@fb.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 0 insertions, 15 deletions

diff --git a/kernel/bpf/map_in_map.c b/kernel/bpf/map_in_map.c
index 38136ec4e095..2c5c64c2a53b 100644
--- a/kernel/bpf/map_in_map.c
+++ b/kernel/bpf/map_in_map.c
@@ -56,18 +56,6 @@ struct bpf_map *bpf_map_meta_alloc(int inner_map_ufd)
 		ret = PTR_ERR(inner_map_meta->record);
 		goto free;
 	}
-	if (inner_map_meta->record) {
-		struct btf_field_offs *field_offs;
-		/* If btf_record is !IS_ERR_OR_NULL, then field_offs is always
-		 * valid.
-		 */
-		field_offs = kmemdup(inner_map->field_offs, sizeof(*inner_map->field_offs), GFP_KERNEL | __GFP_NOWARN);
-		if (!field_offs) {
-			ret = -ENOMEM;
-			goto free_rec;
-		}
-		inner_map_meta->field_offs = field_offs;
-	}
 	/* Note: We must use the same BTF, as we also used btf_record_dup above
 	 * which relies on BTF being same for both maps, as some members like
 	 * record->fields.list_head have pointers like value_rec pointing into
@@ -88,8 +76,6 @@ struct bpf_map *bpf_map_meta_alloc(int inner_map_ufd)
 
 	fdput(f);
 	return inner_map_meta;
-free_rec:
-	btf_record_free(inner_map_meta->record);
 free:
 	kfree(inner_map_meta);
 put:
@@ -99,7 +85,6 @@ put:
 
 void bpf_map_meta_free(struct bpf_map *map_meta)
 {
-	kfree(map_meta->field_offs);
 	bpf_map_free_record(map_meta);
 	btf_put(map_meta->btf);
 	kfree(map_meta);