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From: Stefan Metzmacher <metze@samba.org>
To: Jens Axboe <axboe@kernel.dk>, "Darrick J. Wong" <djwong@kernel.org>
Cc: io-uring@vger.kernel.org
Subject: Re: [PATCH 2/5] io_uring: add support for IORING_OP_URING_CMD
Date: Sat, 20 Feb 2021 04:57:52 +0100	[thread overview]
Message-ID: <81d6c90e-b853-27c0-c4b7-23605bd4abae@samba.org> (raw)
In-Reply-To: <f8576940-5441-1355-c09e-db60ad0ac889@kernel.dk>


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Hi Jens,

Am 28.01.21 um 03:19 schrieb Jens Axboe:
>>> Assuming that I got that right, that means that the pdu information
>>> doesn't actually go all the way to the end of the sqe, which currently
>>> is just a bunch of padding.  Was that intentional, or does this mean
>>> that io_uring_pdu could actually be 8 bytes longer?
>>
>> Also correct. The reason is actually kind of stupid, and I think we
>> should just fix that up. struct io_uring_cmd should fit within the first
>> cacheline of io_kiocb, to avoid bloating that one. But with the members
>> in there, it ends up being 8 bytes too big, if we grab those 8 bytes.
>> What I think we should do is get rid of ->done, and just have drivers
>> call io_uring_cmd_done() instead. We can provide an empty hook for that.
>> Then we can reclaim the 8 bytes, and grow the io_uring_cmd to 56 bytes.
> 
> Pushed out that version:
> 
> https://git.kernel.dk/cgit/linux-block/log/?h=io_uring-fops.v2
> 
> which gives you the full 56 bytes for the payload command.

I think we only have 48 bytes for the payload.

I've rebased and improved your io_uring-fops.v2 on top of your io_uring-worker.v3.

See https://git.samba.org/?p=metze/linux/wip.git;a=shortlog;h=refs/heads/io_uring-fops

I've changed the layout like this:

struct io_uring_sqe {
        __u8    opcode;         /* type of operation for this sqe */
        __u8    flags;          /* IOSQE_ flags */
        union {
                __u16   ioprio;         /* ioprio for the request */
                __u16   cmd_personality; /* IORING_OP_URING_CMD */
        };
        __s32   fd;             /* file descriptor to do IO on */
        union {
                __u64   off;    /* offset into file */
                __u64   addr2;
                __u64   cmd_user_data; /* IORING_OP_URING_CMD: data to be passed back at completion time */
        };
        union {
                __u64   addr;   /* pointer to buffer or iovecs */
                __u64   splice_off_in;
                __u64   cmd_pdu_start; /* IORING_OP_URING_CMD: this is the start for the remaining 48 bytes */
        };

And then use:

struct io_uring_cmd_pdu {
       __u64 data[6]; /* 48 bytes available for free use */
};

So we effectively have this:

struct io_uring_cmd_sqe {
        __u8    opcode;         /* type of operation for this sqe */
        __u8    flags;          /* IOSQE_ flags */
        __u16   cmd_personality; /* IORING_OP_URING_CMD */
        __s32   fd;             /* file descriptor to do IO on */
        __u64   cmd_user_data; /* IORING_OP_URING_CMD: data to be passed back at completion time */
        union {
                __u64   cmd_pdu_start; /* IORING_OP_URING_CMD: this is the start for the remaining 48 bytes */
                struct io_uring_cmd_pdu cmd_pdu;
        };
}

I think it's saner to have a complete block of 48 bytes available for the payload
and move personality and user_data to to top if opcode is IORING_OP_URING_CMD
instead of having a hole that can't be touched.

I also finished the socket glue from struct file -> struct socket -> struct sock

I think it compiles, but I haven't done any tests.

What do you think?
metze


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  reply	other threads:[~2021-02-20  3:58 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-27 21:25 [PATCHSET RFC 0/5] file_operations based io_uring commands Jens Axboe
2021-01-27 21:25 ` [PATCH 1/5] fs: add file_operations->uring_cmd() Jens Axboe
2021-01-27 21:25 ` [PATCH 2/5] io_uring: add support for IORING_OP_URING_CMD Jens Axboe
2021-01-28  0:38   ` Darrick J. Wong
2021-01-28  1:45     ` Jens Axboe
2021-01-28  2:19       ` Jens Axboe
2021-02-20  3:57         ` Stefan Metzmacher [this message]
2021-02-20 14:50           ` Jens Axboe
2021-02-20 16:45             ` Jens Axboe
2021-02-22 20:04               ` Stefan Metzmacher
2021-02-22 20:14                 ` Jens Axboe
2021-02-23  8:14                   ` Stefan Metzmacher
2021-02-23 13:21                     ` Pavel Begunkov
2021-01-27 21:25 ` [PATCH 3/5] block: wire up support for file_operations->uring_cmd() Jens Axboe
2021-01-27 21:25 ` [PATCH 4/5] block: add example ioctl Jens Axboe
2021-01-27 21:25 ` [PATCH 5/5] net: wire up support for file_operations->uring_cmd() Jens Axboe

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