Re: [RFC PATCH v1 07/10] bpf: add kfuncs and helpers support for file dynptrs

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

On 10/3/25 22:35, Eduard Zingerman wrote:
> On Fri, 2025-10-03 at 17:04 +0100, Mykyta Yatsenko wrote:
>
> [...]
>
>> @@ -1702,6 +1733,25 @@ int bpf_dynptr_check_size(u64 size)
>>   	return size > DYNPTR_MAX_SIZE ? -E2BIG : 0;
>>   }
>>   
>> +static int bpf_file_fetch_bytes(struct bpf_dynptr_file_impl *df, u64 offset, void *buf, u64 len)
>> +{
>> +	const void *ptr;
>> +
>> +	if (!buf || len == 0)
>> +		return -EINVAL;
>> +
>> +	df->freader.buf = buf;
>> +	df->freader.buf_sz = len;
>> +	ptr = freader_fetch(&df->freader, offset + df->offset, len);
> What will happen, if file does not have enough data to read `len` bytes?
> Will freader_fetch() return NULL?
yes, that's what should happen, freader will try to load folio after the 
last one,
which should fail and return NULL.
>
>> +	if (!ptr)
>> +		return df->freader.err;
>> +
>> +	if (ptr != buf) /* Force copying into the buffer */
>> +		memcpy(buf, ptr, len);
>> +
>> +	return 0;
>> +}
>> +
>>   void bpf_dynptr_init(struct bpf_dynptr_kern *ptr, void *data,
>>   		     enum bpf_dynptr_type type, u32 offset, u32 size)
>>   {
> [...]