// SPDX-License-Identifier: GPL-2.0-only
/* Copyright (c) 2024 Google */
#include <linux/bpf.h>
#include <linux/btf_ids.h>
#include <linux/slab.h>
#include <linux/kernel.h>
#include <linux/seq_file.h>

#include "../../mm/slab.h" /* kmem_cache, slab_caches and slab_mutex */

/* open-coded version */
struct bpf_iter_kmem_cache {
        __u64 __opaque[1];
} __attribute__((aligned(8)));

struct bpf_iter_kmem_cache_kern {
        struct kmem_cache *pos;
} __attribute__((aligned(8)));

#define KMEM_CACHE_POS_START  ((void *)1L)

__bpf_kfunc_start_defs();

__bpf_kfunc int bpf_iter_kmem_cache_new(struct bpf_iter_kmem_cache *it)
{
        struct bpf_iter_kmem_cache_kern *kit = (void *)it;

        BUILD_BUG_ON(sizeof(*kit) > sizeof(*it));
        BUILD_BUG_ON(__alignof__(*kit) != __alignof__(*it));

        kit->pos = KMEM_CACHE_POS_START;
        return 0;
}

__bpf_kfunc struct kmem_cache *bpf_iter_kmem_cache_next(struct bpf_iter_kmem_cache *it)
{
        struct bpf_iter_kmem_cache_kern *kit = (void *)it;
        struct kmem_cache *prev = kit->pos;
        struct kmem_cache *next;
        bool destroy = false;

        if (!prev)
                return NULL;

        mutex_lock(&slab_mutex);

        if (list_empty(&slab_caches)) {
                mutex_unlock(&slab_mutex);
                return NULL;
        }

        if (prev == KMEM_CACHE_POS_START)
                next = list_first_entry(&slab_caches, struct kmem_cache, list);
        else if (list_last_entry(&slab_caches, struct kmem_cache, list) == prev)
                next = NULL;
        else
                next = list_next_entry(prev, list);

        /* boot_caches have negative refcount, don't touch them */
        if (next && next->refcount > 0)
                next->refcount++;

        /* Skip kmem_cache_destroy() for active entries */
        if (prev && prev != KMEM_CACHE_POS_START) {
                if (prev->refcount > 1)
                        prev->refcount--;
                else if (prev->refcount == 1)
                        destroy = true;
        }

        mutex_unlock(&slab_mutex);

        if (destroy)
                kmem_cache_destroy(prev);

        kit->pos = next;
        return next;
}

__bpf_kfunc void bpf_iter_kmem_cache_destroy(struct bpf_iter_kmem_cache *it)
{
        struct bpf_iter_kmem_cache_kern *kit = (void *)it;
        struct kmem_cache *s = kit->pos;
        bool destroy = false;

        if (s == NULL || s == KMEM_CACHE_POS_START)
                return;

        mutex_lock(&slab_mutex);

        /* Skip kmem_cache_destroy() for active entries */
        if (s->refcount > 1)
                s->refcount--;
        else if (s->refcount == 1)
                destroy = true;

        mutex_unlock(&slab_mutex);

        if (destroy)
                kmem_cache_destroy(s);
}

__bpf_kfunc_end_defs();

struct bpf_iter__kmem_cache {
        __bpf_md_ptr(struct bpf_iter_meta *, meta);
        __bpf_md_ptr(struct kmem_cache *, s);
};

union kmem_cache_iter_priv {
        struct bpf_iter_kmem_cache it;
        struct bpf_iter_kmem_cache_kern kit;
};

static void *kmem_cache_iter_seq_start(struct seq_file *seq, loff_t *pos)
{
        loff_t cnt = 0;
        bool found = false;
        struct kmem_cache *s;
        union kmem_cache_iter_priv *p = seq->private;

        mutex_lock(&slab_mutex);

        /* Find an entry at the given position in the slab_caches list instead
         * of keeping a reference (of the last visited entry, if any) out of
         * slab_mutex. It might miss something if one is deleted in the middle
         * while it releases the lock.  But it should be rare and there's not
         * much we can do about it.
         */
        list_for_each_entry(s, &slab_caches, list) {
                if (cnt == *pos) {
                        /* Make sure this entry remains in the list by getting
                         * a new reference count.  Note that boot_cache entries
                         * have a negative refcount, so don't touch them.
                         */
                        if (s->refcount > 0)
                                s->refcount++;
                        found = true;
                        break;
                }
                cnt++;
        }
        mutex_unlock(&slab_mutex);

        if (!found)
                s = NULL;

        p->kit.pos = s;
        return s;
}

static void kmem_cache_iter_seq_stop(struct seq_file *seq, void *v)
{
        struct bpf_iter_meta meta;
        struct bpf_iter__kmem_cache ctx = {
                .meta = &meta,
                .s = v,
        };
        union kmem_cache_iter_priv *p = seq->private;
        struct bpf_prog *prog;

        meta.seq = seq;
        prog = bpf_iter_get_info(&meta, true);
        if (prog && !ctx.s)
                bpf_iter_run_prog(prog, &ctx);

        bpf_iter_kmem_cache_destroy(&p->it);
}

static void *kmem_cache_iter_seq_next(struct seq_file *seq, void *v, loff_t *pos)
{
        union kmem_cache_iter_priv *p = seq->private;

        ++*pos;

        return bpf_iter_kmem_cache_next(&p->it);
}

static int kmem_cache_iter_seq_show(struct seq_file *seq, void *v)
{
        struct bpf_iter_meta meta;
        struct bpf_iter__kmem_cache ctx = {
                .meta = &meta,
                .s = v,
        };
        struct bpf_prog *prog;
        int ret = 0;

        meta.seq = seq;
        prog = bpf_iter_get_info(&meta, false);
        if (prog)
                ret = bpf_iter_run_prog(prog, &ctx);

        return ret;
}

static const struct seq_operations kmem_cache_iter_seq_ops = {
        .start  = kmem_cache_iter_seq_start,
        .next   = kmem_cache_iter_seq_next,
        .stop   = kmem_cache_iter_seq_stop,
        .show   = kmem_cache_iter_seq_show,
};

BTF_ID_LIST_GLOBAL_SINGLE(bpf_kmem_cache_btf_id, struct, kmem_cache)

static const struct bpf_iter_seq_info kmem_cache_iter_seq_info = {
        .seq_ops                = &kmem_cache_iter_seq_ops,
        .seq_priv_size          = sizeof(union kmem_cache_iter_priv),
};

static void bpf_iter_kmem_cache_show_fdinfo(const struct bpf_iter_aux_info *aux,
                                            struct seq_file *seq)
{
        seq_puts(seq, "kmem_cache iter\n");
}

DEFINE_BPF_ITER_FUNC(kmem_cache, struct bpf_iter_meta *meta,
                     struct kmem_cache *s)

static struct bpf_iter_reg bpf_kmem_cache_reg_info = {
        .target                 = "kmem_cache",
        .feature                = BPF_ITER_RESCHED,
        .show_fdinfo            = bpf_iter_kmem_cache_show_fdinfo,
        .ctx_arg_info_size      = 1,
        .ctx_arg_info           = {
                { offsetof(struct bpf_iter__kmem_cache, s),
                  PTR_TO_BTF_ID_OR_NULL | PTR_TRUSTED },
        },
        .seq_info               = &kmem_cache_iter_seq_info,
};

static int __init bpf_kmem_cache_iter_init(void)
{
        bpf_kmem_cache_reg_info.ctx_arg_info[0].btf_id = bpf_kmem_cache_btf_id[0];
        return bpf_iter_reg_target(&bpf_kmem_cache_reg_info);
}

late_initcall(bpf_kmem_cache_iter_init);