Re: [PATCH 5.11] io_uring: don't take fs for recvmsg/sendmsg

[Stefan Metzmacher <metze@samba.org>]

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Am 18.11.20 um 17:27 schrieb Stefan Metzmacher:
> Am 07.11.20 um 17:07 schrieb Pavel Begunkov:
>> On 07/11/2020 16:02, Pavel Begunkov wrote:
>>> On 07/11/2020 13:46, Stefan Metzmacher wrote:
>>>> Hi Pavel,
>>>>
>>>>> We don't even allow not plain data msg_control, which is disallowed in __sys_{send,revb}msg_sock().
>>>>
>>>> Can't we better remove these checks and allow msg_control?
>>>> For me it's a limitation that I would like to be removed.
>>>
>>> We can grab fs only in specific situations as you mentioned, by e.g.
>>> adding a switch(opcode) in io_prep_async_work(), but that's the easy
>>> part. All msg_control should be dealt one by one as they do different
>>> things. And it's not the fact that they ever require fs.
>>
>> BTW, Jens mentioned that there is a queued patch that allows plain
>> data msg_control. Are those not enough?
> 
> You mean the PROTO_CMSG_DATA_ONLY check?
> 
> It's not perfect, but better than nothing for a start.

What actually have in mind for my smbdirect socket driver [1]:

- I have a pipe that got filled by IORING_OP_SPLICE
- The data in the pipe need to be "spliced" into a remote RDMA buffers,
  but I can't use IORING_OP_SPLICE again, because the RDMA buffer descriptor [2]
  array needs to be passed too.
- I'd like to use IORING_OP_SENDMSG with MSG_OOB and msg_control.
  msg_control would get the RDMA buffer descriptor array and the pipe fd.

The reverse operation (splicing data from remote RDMA buffers into a pipe)
would be implemented with IORING_OP_RECVMSG with MSG_OOB and msg_control.

I guess my smbdirect socket driver would not qualify to be marked as PROTO_CMSG_DATA_ONLY, correct?

[1] https://git.samba.org/?p=metze/linux/smbdirect.git;a=blob;f=smbdirect_socket.c;h=a738854462b198e#l2076
[2] https://docs.microsoft.com/ru-ru/openspecs/windows_protocols/ms-smbd/bee890cb-48f0-42a3-ba62-f1a3a19b0edc

metze


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