Re: [PATCH bpf-next v3 10/10] selftests/bpf: add file dynptr tests

[Mykyta Yatsenko <mykyta.yatsenko5@gmail.com>]

On 10/21/25 01:45, Eduard Zingerman wrote:
> On Mon, 2025-10-20 at 23:25 +0100, Mykyta Yatsenko wrote:
>> From: Mykyta Yatsenko <yatsenko@meta.com>
>>
>> Introducing selftests for validating file-backed dynptr works as
>> expected.
>>   * validate implementation supports dynptr slice and read operations
>>   * validate destructors should be paired with initializers
>>   * validate sleepable progs can page in.
>>
>> Signed-off-by: Mykyta Yatsenko <yatsenko@meta.com>
>> ---
> [...]
>
>> diff --git a/tools/testing/selftests/bpf/progs/file_reader.c b/tools/testing/selftests/bpf/progs/file_reader.c
>> new file mode 100644
>> index 000000000000..695ef6392771
>> --- /dev/null
>> +++ b/tools/testing/selftests/bpf/progs/file_reader.c
>> @@ -0,0 +1,178 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +/* Copyright (c) 2025 Meta Platforms, Inc. and affiliates. */
>> +
>> +#include <vmlinux.h>
>> +#include <string.h>
>> +#include <stdbool.h>
>> +#include <bpf/bpf_tracing.h>
>> +#include "bpf_misc.h"
>> +#include "errno.h"
>> +
>> +char _license[] SEC("license") = "GPL";
>> +
>> +struct {
>> +	__uint(type, BPF_MAP_TYPE_ARRAY);
>> +	__uint(max_entries, 1);
>> +	__type(key, int);
>> +	__type(value, struct elem);
>> +} arrmap SEC(".maps");
>> +
>> +struct {
>> +	__uint(type, BPF_MAP_TYPE_RINGBUF);
>> +	__uint(max_entries, 10000000);
>> +} ringbuf SEC(".maps");
> The test case lgtm, but a question: will it be possible to use an
> array map instead of a ringbuf?  Just to avoid the need to allocate
> and discard the pointer.
How do I use array map here? Should I set a map value to be a buffer of
needed length (256KB) or use 1 byte value and 256K elements in the map?
Honestly, both options seem a little awkward to me, but I'm not sure 
maybe it is an
expected way to get a big buffer.
I like allocation/discard, as it guarantees that this temporary buffer 
is local to the
current func execution and we need to run non-trivial deinitialization 
anyway.
>
> [...]
>
>> diff --git a/tools/testing/selftests/bpf/progs/file_reader_fail.c b/tools/testing/selftests/bpf/progs/file_reader_fail.c
>> new file mode 100644
>> index 000000000000..32fe28ed2439
>> --- /dev/null
>> +++ b/tools/testing/selftests/bpf/progs/file_reader_fail.c
> Thank you for adding these.
>
> [...]