Re: [PATCH v5 net-next 3/7] net: ethtool: record custom RSS contexts in the XArray

[Edward Cree <ecree.xilinx@gmail.com>]

On 19/06/2024 01:46, David Wei wrote:
> On 2024-06-18 15:44, edward.cree@amd.com wrote:
>> From: Edward Cree <ecree.xilinx@gmail.com>
>>
>> Since drivers are still choosing the context IDs, we have to force the
>>  XArray to use the ID they've chosen rather than picking one ourselves,
>>  and handle the case where they give us an ID that's already in use.
>>
>> Signed-off-by: Edward Cree <ecree.xilinx@gmail.com>
>> ---
>>  include/linux/ethtool.h | 14 ++++++++
>>  net/ethtool/ioctl.c     | 74 ++++++++++++++++++++++++++++++++++++++++-
>>  2 files changed, 87 insertions(+), 1 deletion(-)
>>
>> diff --git a/include/linux/ethtool.h b/include/linux/ethtool.h
>> index a68b83a6d61f..5bef46fdcb94 100644
>> --- a/include/linux/ethtool.h
>> +++ b/include/linux/ethtool.h
>> @@ -199,6 +199,17 @@ static inline u8 *ethtool_rxfh_context_key(struct ethtool_rxfh_context *ctx)
>>  	return (u8 *)(ethtool_rxfh_context_indir(ctx) + ctx->indir_size);
>>  }
>>  
>> +static inline size_t ethtool_rxfh_context_size(u32 indir_size, u32 key_size,
>> +					       u16 priv_size)
>> +{
>> +	size_t indir_bytes = array_size(indir_size, sizeof(u32));
>> +	size_t flex_len;
>> +
>> +	flex_len = size_add(size_add(indir_bytes, key_size),
>> +			    ALIGN(priv_size, sizeof(u32)));
>> +	return struct_size((struct ethtool_rxfh_context *)0, data, flex_len);
> 
> ctx->data is [ priv | indir_tbl | key ] but only priv and indir_tbl are
> aligned to sizeof(u32). Why does key not need to be aligned?

Because it's a u8[], whereas indir_tbl is a u32[].
(And priv is aligned to sizeof(void *), so that drivers can put
 whatever struct they like there and have proper alignment.)

> Is it guaranteed to be 40 bytes?

Not AFAIK, though that certainly is a popular size.

-ed