bpf: Refactor map->off_arr handling

Refactor map->off_arr handling into generic functions that can work on
their own without hardcoding map specific code. The btf_fields_offs
structure is now returned from btf_parse_field_offs, which can be reused
later for types in program BTF.

All functions like copy_map_value, zero_map_value call generic
underlying functions so that they can also be reused later for copying
to values allocated in programs which encode specific fields.

Later, some helper functions will also require access to this
btf_field_offs structure to be able to skip over special fields at
runtime.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20221103191013.1236066-9-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 55 insertions, 0 deletions

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 3dad828db13c..5579ff3a5b54 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -3551,6 +3551,61 @@ end:
 	return ERR_PTR(ret);
 }
 
+static int btf_field_offs_cmp(const void *_a, const void *_b, const void *priv)
+{
+	const u32 a = *(const u32 *)_a;
+	const u32 b = *(const u32 *)_b;
+
+	if (a < b)
+		return -1;
+	else if (a > b)
+		return 1;
+	return 0;
+}
+
+static void btf_field_offs_swap(void *_a, void *_b, int size, const void *priv)
+{
+	struct btf_field_offs *foffs = (void *)priv;
+	u32 *off_base = foffs->field_off;
+	u32 *a = _a, *b = _b;
+	u8 *sz_a, *sz_b;
+
+	sz_a = foffs->field_sz + (a - off_base);
+	sz_b = foffs->field_sz + (b - off_base);
+
+	swap(*a, *b);
+	swap(*sz_a, *sz_b);
+}
+
+struct btf_field_offs *btf_parse_field_offs(struct btf_record *rec)
+{
+	struct btf_field_offs *foffs;
+	u32 i, *off;
+	u8 *sz;
+
+	BUILD_BUG_ON(ARRAY_SIZE(foffs->field_off) != ARRAY_SIZE(foffs->field_sz));
+	if (IS_ERR_OR_NULL(rec) || WARN_ON_ONCE(rec->cnt > sizeof(foffs->field_off)))
+		return NULL;
+
+	foffs = kzalloc(sizeof(*foffs), GFP_KERNEL | __GFP_NOWARN);
+	if (!foffs)
+		return ERR_PTR(-ENOMEM);
+
+	off = foffs->field_off;
+	sz = foffs->field_sz;
+	for (i = 0; i < rec->cnt; i++) {
+		off[i] = rec->fields[i].offset;
+		sz[i] = btf_field_type_size(rec->fields[i].type);
+	}
+	foffs->cnt = rec->cnt;
+
+	if (foffs->cnt == 1)
+		return foffs;
+	sort_r(foffs->field_off, foffs->cnt, sizeof(foffs->field_off[0]),
+	       btf_field_offs_cmp, btf_field_offs_swap, foffs);
+	return foffs;
+}
+
 static void __btf_struct_show(const struct btf *btf, const struct btf_type *t,
 			      u32 type_id, void *data, u8 bits_offset,
 			      struct btf_show *show)