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([2620:10d:c092:500::5:3ecd]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-43ead3fd3b7sm4842013f8f.35.2026.04.15.04.15.22 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 15 Apr 2026 04:15:22 -0700 (PDT) Message-ID: Date: Wed, 15 Apr 2026 12:15:19 +0100 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH RFC bpf-next v2 08/18] bpf: Implement iterator APIs for resizable hashtab To: Emil Tsalapatis , bpf@vger.kernel.org, ast@kernel.org, andrii@kernel.org, daniel@iogearbox.net, kafai@meta.com, kernel-team@meta.com, eddyz87@gmail.com, memxor@gmail.com, herbert@gondor.apana.org.au Cc: Mykyta Yatsenko References: <20260408-rhash-v2-0-3b3675da1f6e@meta.com> <20260408-rhash-v2-8-3b3675da1f6e@meta.com> Content-Language: en-US From: Mykyta Yatsenko In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 4/14/26 6:49 PM, Emil Tsalapatis wrote: > On Wed Apr 8, 2026 at 11:10 AM EDT, Mykyta Yatsenko wrote: >> From: Mykyta Yatsenko >> >> Wire up seq_file BPF iterator for BPF_MAP_TYPE_RHASH so that >> bpf_iter and bpftool map dump work with resizable hash maps. >> >> Use rhashtable_walk_enter_from() with a saved last_key to resume >> iteration across read() calls without linear skip from the >> beginning on each seq_start. >> >> Also implement rhtab_map_seq_show_elem() for bpftool map dump >> in non-iterator mode. >> >> Signed-off-by: Mykyta Yatsenko > > Reviewed-by: Emil Tsalapatis > >> --- >> kernel/bpf/hashtab.c | 98 +++++++++++++++++++++++++++++++++++++++++++++++++--- >> 1 file changed, 94 insertions(+), 4 deletions(-) >> >> diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c >> index a79d434dc626..492c6a9154b6 100644 >> --- a/kernel/bpf/hashtab.c >> +++ b/kernel/bpf/hashtab.c >> @@ -3008,6 +3008,19 @@ static int rhtab_map_get_next_key(struct bpf_map *map, void *key, void *next_key >> >> static void rhtab_map_seq_show_elem(struct bpf_map *map, void *key, struct seq_file *m) >> { >> + void *value; >> + >> + /* Guarantee that hashtab value is not freed */ >> + guard(rcu)(); >> + >> + value = rhtab_map_lookup_elem(map, key); >> + if (!value) >> + return; >> + >> + btf_type_seq_show(map->btf, map->btf_key_type_id, key, m); >> + seq_puts(m, ": "); >> + btf_type_seq_show(map->btf, map->btf_value_type_id, value, m); >> + seq_putc(m, '\n'); >> } >> >> static long bpf_each_rhash_elem(struct bpf_map *map, bpf_callback_t callback_fn, >> @@ -3201,36 +3214,113 @@ struct bpf_iter_seq_rhash_map_info { >> struct bpf_map *map; >> struct bpf_rhtab *rhtab; >> struct rhashtable_iter iter; >> - u32 skip_elems; >> + void *last_key; > > Nit: Could we avoid adding skip_elems to this in the first place since > it's never used? > Definitely yes, thanks for noticing. >> bool iter_active; >> }; >> > > Question: Would it make sense/be worth annotating the seq functions with > __acquires/__releases(RCU)? > I guess it won't hurt. >> static void *bpf_rhash_map_seq_start(struct seq_file *seq, loff_t *pos) >> { >> - return NULL; >> + struct bpf_iter_seq_rhash_map_info *info = seq->private; >> + struct rhtab_elem *elem; >> + void *key = *pos > 0 ? info->last_key : NULL; >> + >> + scoped_guard(rcu) { >> + rhashtable_walk_enter_from(&info->rhtab->ht, &info->iter, >> + key, info->rhtab->params); >> + rhashtable_walk_start(&info->iter); >> + } >> + info->iter_active = true; >> + >> + elem = rhtab_iter_next(&info->iter); >> + if (!elem) >> + return NULL; >> + /* >> + * if *pos is not 0, previously iteration failed on this elem, >> + * so we are restarting it. That's why no need to increment *pos. >> + */ >> + if (*pos == 0) >> + ++*pos; >> + return elem; >> } >> >> static void *bpf_rhash_map_seq_next(struct seq_file *seq, void *v, loff_t *pos) >> { >> - return NULL; >> + struct bpf_iter_seq_rhash_map_info *info = seq->private; >> + struct rhtab_elem *elem = v; >> + >> + /* Save current key for O(1) resume in next seq_start */ >> + memcpy(info->last_key, elem->data, info->map->key_size); >> + >> + ++*pos; >> + >> + return rhtab_iter_next(&info->iter); >> +} >> + >> +static int __bpf_rhash_map_seq_show(struct seq_file *seq, >> + struct rhtab_elem *elem) >> +{ >> + struct bpf_iter_seq_rhash_map_info *info = seq->private; >> + struct bpf_iter__bpf_map_elem ctx = {}; >> + struct bpf_iter_meta meta; >> + struct bpf_prog *prog; >> + int ret = 0; >> + >> + meta.seq = seq; >> + prog = bpf_iter_get_info(&meta, elem == NULL); >> + if (prog) { >> + ctx.meta = &meta; >> + ctx.map = info->map; >> + if (elem) { >> + ctx.key = elem->data; >> + ctx.value = rhtab_elem_value(elem, info->map->key_size); >> + } >> + ret = bpf_iter_run_prog(prog, &ctx); >> + } >> + >> + return ret; >> } >> >> static int bpf_rhash_map_seq_show(struct seq_file *seq, void *v) >> { >> - return 0; >> + return __bpf_rhash_map_seq_show(seq, v); >> } >> >> static void bpf_rhash_map_seq_stop(struct seq_file *seq, void *v) >> { >> + struct bpf_iter_seq_rhash_map_info *info = seq->private; >> + >> + if (!v) >> + (void)__bpf_rhash_map_seq_show(seq, NULL); >> + >> + if (info->iter_active) { >> + rhashtable_walk_stop(&info->iter); >> + rhashtable_walk_exit(&info->iter); >> + info->iter_active = false; >> + } >> } >> >> static int bpf_iter_init_rhash_map(void *priv_data, struct bpf_iter_aux_info *aux) >> { >> + struct bpf_iter_seq_rhash_map_info *info = priv_data; >> + struct bpf_map *map = aux->map; >> + >> + info->last_key = kmalloc(map->key_size, GFP_USER); >> + if (!info->last_key) >> + return -ENOMEM; >> + >> + bpf_map_inc_with_uref(map); >> + info->map = map; >> + info->rhtab = container_of(map, struct bpf_rhtab, map); >> + info->iter_active = false; >> return 0; >> } >> >> static void bpf_iter_fini_rhash_map(void *priv_data) >> { >> + struct bpf_iter_seq_rhash_map_info *info = priv_data; >> + >> + kfree(info->last_key); >> + bpf_map_put_with_uref(info->map); >> } >> >> static const struct seq_operations bpf_rhash_map_seq_ops = { >