// SPDX-License-Identifier: GPL-2.0
/* Copyright (c) 2024 Google */
#include <vmlinux.h>
#include <bpf/bpf_helpers.h>
#include <bpf/bpf_tracing.h>
#include "bpf_experimental.h"

char _license[] SEC("license") = "GPL";

#define SLAB_NAME_MAX  32

struct kmem_cache_result {
        char name[SLAB_NAME_MAX];
        long obj_size;
};

struct {
        __uint(type, BPF_MAP_TYPE_HASH);
        __uint(key_size, sizeof(void *));
        __uint(value_size, SLAB_NAME_MAX);
        __uint(max_entries, 1);
} slab_hash SEC(".maps");

struct {
        __uint(type, BPF_MAP_TYPE_ARRAY);
        __uint(key_size, sizeof(int));
        __uint(value_size, sizeof(struct kmem_cache_result));
        __uint(max_entries, 1024);
} slab_result SEC(".maps");

extern struct kmem_cache *bpf_get_kmem_cache(u64 addr) __ksym;

/* Result, will be checked by userspace */
int task_struct_found;
int kmem_cache_seen;
int open_coded_seen;

SEC("iter/kmem_cache")
int slab_info_collector(struct bpf_iter__kmem_cache *ctx)
{
        struct seq_file *seq = ctx->meta->seq;
        struct kmem_cache *s = ctx->s;
        struct kmem_cache_result *r;
        int idx;

        if (s) {
                /* To make sure if the slab_iter implements the seq interface
                 * properly and it's also useful for debugging.
                 */
                BPF_SEQ_PRINTF(seq, "%s: %u\n", s->name, s->size);

                idx = kmem_cache_seen;
                r = bpf_map_lookup_elem(&slab_result, &idx);
                if (r == NULL)
                        return 0;

                kmem_cache_seen++;

                /* Save name and size to match /proc/slabinfo */
                bpf_probe_read_kernel_str(r->name, sizeof(r->name), s->name);
                r->obj_size = s->size;

                if (!bpf_strncmp(r->name, 11, "task_struct"))
                        bpf_map_update_elem(&slab_hash, &s, r->name, BPF_NOEXIST);
        }

        return 0;
}

SEC("raw_tp/bpf_test_finish")
int BPF_PROG(check_task_struct)
{
        u64 curr = bpf_get_current_task();
        struct kmem_cache *s;
        char *name;

        s = bpf_get_kmem_cache(curr);
        if (s == NULL) {
                task_struct_found = -1;
                return 0;
        }
        name = bpf_map_lookup_elem(&slab_hash, &s);
        if (name && !bpf_strncmp(name, 11, "task_struct"))
                task_struct_found = 1;
        else
                task_struct_found = -2;
        return 0;
}

SEC("syscall")
int open_coded_iter(const void *ctx)
{
        struct kmem_cache *s;

        bpf_for_each(kmem_cache, s) {
                struct kmem_cache_result *r;

                r = bpf_map_lookup_elem(&slab_result, &open_coded_seen);
                if (!r)
                        break;

                if (r->obj_size != s->size)
                        break;

                open_coded_seen++;
        }
        return 0;
}