Hi,
On 2/14/2025 8:13 AM, Alexei Starovoitov wrote:
> On Sat, Jan 25, 2025 at 2:59 AM Hou Tao <houtao@xxxxxxxxxxxxxxx> wrote:
>> From: Hou Tao <houtao1@xxxxxxxxxx>
>>
>> For bpf map with dynptr key support, the userspace application will use
>> bpf_dynptr_user to represent the bpf_dynptr in the map key and pass it
>> to bpf syscall. The bpf syscall will copy from bpf_dynptr_user to
>> construct a corresponding bpf_dynptr_kern object when the map key is an
>> input argument, and copy to bpf_dynptr_user from a bpf_dynptr_kern
>> object when the map key is an output argument.
>>
>> For now the size of bpf_dynptr_user must be the same as bpf_dynptr, but
>> the last u32 field is not used, so make it a reserved field.
>>
>> Signed-off-by: Hou Tao <houtao1@xxxxxxxxxx>
>> ---
>> include/uapi/linux/bpf.h | 6 ++++++
>> tools/include/uapi/linux/bpf.h | 6 ++++++
>> 2 files changed, 12 insertions(+)
>>
>> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
>> index 2acf9b3363717..7d96685513c55 100644
>> --- a/include/uapi/linux/bpf.h
>> +++ b/include/uapi/linux/bpf.h
>> @@ -7335,6 +7335,12 @@ struct bpf_dynptr {
>> __u64 __opaque[2];
>> } __attribute__((aligned(8)));
>>
>> +struct bpf_dynptr_user {
>> + __bpf_md_ptr(void *, data);
>> + __u32 size;
>> + __u32 reserved;
>> +} __attribute__((aligned(8)));
> Pls add a comment explaining that bpf_dynptr_user is for user space only
> and bpf progs should continue using bpf_dynptr.
> May be give an example that to use bpf_dynptr in map key
> the bpf prog should write:
>
> +struct mixed_dynptr_key {
> + int id;
> + struct bpf_dynptr name;
> +};
>
> while to access that map the user space should write:
>
> +struct id_dname_key {
> + int id;
> + struct bpf_dynptr_user name;
> +};
Will add comments for the {data,size} tuple case.
>
> tbh the api is kinda ugly, since in the past we always had user space
> and bpf prog reuse the same struct names.
> Here the top struct names have to be different,
> but have to have the same layout.
>
> Maybe let's try the following:
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index fff6cdb8d11a..55d225961dbf 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -7335,7 +7335,14 @@ struct bpf_wq {
> } __attribute__((aligned(8)));
>
> struct bpf_dynptr {
> + union {
> __u64 __opaque[2];
> + struct {
> + __bpf_md_ptr(void *, data);
> + __u32 size;
> + __u32 reserved;
> + };
> + };
> } __attribute__((aligned(8)));
>
> Then bpf prog and user space can use the same key type.
> .
It seems a bit strange to combine these two structs, because bpf prog
uses bpf_dynptr as an opaque object, but user space application uses
bpf_dynptr as a {data,size} tuple. However, I don't have better idea.
Will switch to that in v3.
