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From: Jens Axboe <[email protected]>
To: Kanchan Joshi <[email protected]>
Cc: Kanchan Joshi <[email protected]>,
	Christoph Hellwig <[email protected]>,
	[email protected], [email protected],
	Pavel Begunkov <[email protected]>,
	Ming Lei <[email protected]>,
	Luis Chamberlain <[email protected]>, Stefan Roesch <[email protected]>,
	Anuj Gupta <[email protected]>,
	[email protected]
Subject: Re: [PATCH v4 1/5] fs,io_uring: add infrastructure for uring-cmd
Date: Tue, 10 May 2022 08:35:36 -0600	[thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <CA+1E3r+airL_U0BzmLhiVPVkWdbiAXxxyHXONy9bGx4uuJFhdA@mail.gmail.com>

On 5/10/22 8:23 AM, Kanchan Joshi wrote:
> On Thu, May 5, 2022 at 9:47 PM Jens Axboe <[email protected]> wrote:
>>
>> On 5/5/22 12:06 AM, Kanchan Joshi wrote:
>>> +static int io_uring_cmd_prep(struct io_kiocb *req,
>>> +                          const struct io_uring_sqe *sqe)
>>> +{
>>> +     struct io_uring_cmd *ioucmd = &req->uring_cmd;
>>> +     struct io_ring_ctx *ctx = req->ctx;
>>> +
>>> +     if (ctx->flags & IORING_SETUP_IOPOLL)
>>> +             return -EOPNOTSUPP;
>>> +     /* do not support uring-cmd without big SQE/CQE */
>>> +     if (!(ctx->flags & IORING_SETUP_SQE128))
>>> +             return -EOPNOTSUPP;
>>> +     if (!(ctx->flags & IORING_SETUP_CQE32))
>>> +             return -EOPNOTSUPP;
>>> +     if (sqe->ioprio || sqe->rw_flags)
>>> +             return -EINVAL;
>>> +     ioucmd->cmd = sqe->cmd;
>>> +     ioucmd->cmd_op = READ_ONCE(sqe->cmd_op);
>>> +     return 0;
>>> +}
>>
>> While looking at the other suggested changes, I noticed a more
>> fundamental issue with the passthrough support. For any other command,
>> SQE contents are stable once prep has been done. The above does do that
>> for the basic items, but this case is special as the lower level command
>> itself resides in the SQE.
>>
>> For cases where the command needs deferral, it's problematic. There are
>> two main cases where this can happen:
>>
>> - The issue attempt yields -EAGAIN (we ran out of requests, etc). If you
>>   look at other commands, if they have data that doesn't fit in the
>>   io_kiocb itself, then they need to allocate room for that data and have
>>   it be persistent
> 
> While we have io-wq retrying for this case, async_data is not allocated.
> We need to do that explicitly inside io_uring_cmd(). Something like this -
> 
> if (ret == -EAGAIN) {
> if (!req_has_async_data(req)) {
> if (io_alloc_async_data(req)) return -ENOMEM;
> io_uring_cmd_prep_async(req);
> }
> return ret;
> }
> 
>> - Deferral is specified by the application, using eg IOSQE_IO_LINK or
>>   IOSQE_ASYNC.
> For this to work, we are missing ".needs_async_setup = 1" for
> IORING_OP_URING_CMD.

Agree on both, the op handler itself should alloc the async_data for
this case and that flag does need to be set.

-- 
Jens Axboe


  reply	other threads:[~2022-05-10 15:05 UTC|newest]

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <CGME20220505061142epcas5p2c943572766bfd5088138fe0f7873c96c@epcas5p2.samsung.com>
2022-05-05  6:06 ` [PATCH v4 0/5] io_uring passthrough for nvme Kanchan Joshi
     [not found]   ` <CGME20220505061144epcas5p3821a9516dad2b5eff5a25c56dbe164df@epcas5p3.samsung.com>
2022-05-05  6:06     ` [PATCH v4 1/5] fs,io_uring: add infrastructure for uring-cmd Kanchan Joshi
2022-05-05 12:52       ` Jens Axboe
2022-05-05 13:48         ` Ming Lei
2022-05-05 13:54           ` Jens Axboe
2022-05-05 13:29       ` Christoph Hellwig
2022-05-05 16:17       ` Jens Axboe
2022-05-05 17:04         ` Jens Axboe
2022-05-06  7:12         ` Kanchan Joshi
2022-05-10 14:23         ` Kanchan Joshi
2022-05-10 14:35           ` Jens Axboe [this message]
     [not found]   ` <CGME20220505061146epcas5p3919c48d58d353a62a5858ee10ad162a0@epcas5p3.samsung.com>
2022-05-05  6:06     ` [PATCH v4 2/5] block: wire-up support for passthrough plugging Kanchan Joshi
2022-05-05 14:21       ` Ming Lei
     [not found]   ` <CGME20220505061148epcas5p188618b5b15a95cbe48c8c1559a18c994@epcas5p1.samsung.com>
2022-05-05  6:06     ` [PATCH v4 3/5] nvme: refactor nvme_submit_user_cmd() Kanchan Joshi
2022-05-05 13:30       ` Christoph Hellwig
2022-05-05 18:37       ` Clay Mayers
2022-05-05 19:03         ` Jens Axboe
2022-05-05 19:11           ` Jens Axboe
2022-05-05 19:30             ` Clay Mayers
2022-05-05 19:31               ` Jens Axboe
2022-05-05 19:50                 ` hch
2022-05-05 20:44                   ` Jens Axboe
2022-05-06  5:56                     ` hch
     [not found]   ` <CGME20220505061150epcas5p2b60880c541a4b2f144c348834c7cbf0b@epcas5p2.samsung.com>
2022-05-05  6:06     ` [PATCH v4 4/5] nvme: wire-up uring-cmd support for io-passthru on char-device Kanchan Joshi
2022-05-05 13:33       ` Christoph Hellwig
2022-05-05 13:38       ` Jens Axboe
2022-05-05 13:42         ` Christoph Hellwig
2022-05-05 13:50           ` Jens Axboe
2022-05-05 17:23             ` Jens Axboe
2022-05-06  8:28               ` Christoph Hellwig
2022-05-06 13:37                 ` Jens Axboe
2022-05-06 14:50                   ` Christoph Hellwig
2022-05-06 14:57                     ` Jens Axboe
2022-05-07  5:03                       ` Christoph Hellwig
2022-05-07 12:53                         ` Jens Axboe
2022-05-09  6:00                           ` Christoph Hellwig
2022-05-09 12:52                             ` Jens Axboe
     [not found]   ` <CGME20220505061151epcas5p2523dc661a0daf3e6185dee771eade393@epcas5p2.samsung.com>
2022-05-05  6:06     ` [PATCH v4 5/5] nvme: add vectored-io support for uring-cmd Kanchan Joshi
2022-05-05 18:20   ` [PATCH v4 0/5] io_uring passthrough for nvme Jens Axboe
2022-05-05 18:29     ` Jens Axboe
2022-05-06  6:42       ` Kanchan Joshi
2022-05-06 13:14         ` Jens Axboe
2022-05-10  7:20     ` Christoph Hellwig
2022-05-10 12:29       ` Jens Axboe
2022-05-10 14:21         ` Kanchan Joshi

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