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Date:   Fri, 19 Jun 2020 11:41:49 +0200
From:   "javier.gonz@samsung.com" <javier@javigon.com>
To:     Damien Le Moal <Damien.LeMoal@wdc.com>
CC:     Kanchan Joshi <joshi.k@samsung.com>,
        "axboe@kernel.dk" <axboe@kernel.dk>,
        "viro@zeniv.linux.org.uk" <viro@zeniv.linux.org.uk>,
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        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
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        "io-uring@vger.kernel.org" <io-uring@vger.kernel.org>,
        "linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
        "selvakuma.s1@samsung.com" <selvakuma.s1@samsung.com>,
        "nj.shetty@samsung.com" <nj.shetty@samsung.com>
Subject: Re: [PATCH 3/3] io_uring: add support for zone-append
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Jens,

Would you have time to answer a question below in this thread?

On 18.06.2020 11:11, javier.gonz@samsung.com wrote:
>On 18.06.2020 08:47, Damien Le Moal wrote:
>>On 2020/06/18 17:35, javier.gonz@samsung.com wrote:
>>>On 18.06.2020 07:39, Damien Le Moal wrote:
>>>>On 2020/06/18 2:27, Kanchan Joshi wrote:
>>>>>From: Selvakumar S <selvakuma.s1@samsung.com>
>>>>>
>>>>>Introduce three new opcodes for zone-append -
>>>>>
>>>>>   IORING_OP_ZONE_APPEND     : non-vectord, similiar to IORING_OP_WRITE
>>>>>   IORING_OP_ZONE_APPENDV    : vectored, similar to IORING_OP_WRITEV
>>>>>   IORING_OP_ZONE_APPEND_FIXED : append using fixed-buffers
>>>>>
>>>>>Repurpose cqe->flags to return zone-relative offset.
>>>>>
>>>>>Signed-off-by: SelvaKumar S <selvakuma.s1@samsung.com>
>>>>>Signed-off-by: Kanchan Joshi <joshi.k@samsung.com>
>>>>>Signed-off-by: Nitesh Shetty <nj.shetty@samsung.com>
>>>>>Signed-off-by: Javier Gonzalez <javier.gonz@samsung.com>
>>>>>---
>>>>> fs/io_uring.c                 | 72 +++++++++++++++++++++++++++++++++++++++++--
>>>>> include/uapi/linux/io_uring.h |  8 ++++-
>>>>> 2 files changed, 77 insertions(+), 3 deletions(-)
>>>>>
>>>>>diff --git a/fs/io_uring.c b/fs/io_uring.c
>>>>>index 155f3d8..c14c873 100644
>>>>>--- a/fs/io_uring.c
>>>>>+++ b/fs/io_uring.c
>>>>>@@ -649,6 +649,10 @@ struct io_kiocb {
>>>>> 	unsigned long		fsize;
>>>>> 	u64			user_data;
>>>>> 	u32			result;
>>>>>+#ifdef CONFIG_BLK_DEV_ZONED
>>>>>+	/* zone-relative offset for append, in bytes */
>>>>>+	u32			append_offset;
>>>>
>>>>this can overflow. u64 is needed.
>>>
>>>We chose to do it this way to start with because struct io_uring_cqe
>>>only has space for u32 when we reuse the flags.
>>>
>>>We can of course create a new cqe structure, but that will come with
>>>larger changes to io_uring for supporting append.
>>>
>>>Do you believe this is a better approach?
>>
>>The problem is that zone size are 32 bits in the kernel, as a number of sectors.
>>So any device that has a zone size smaller or equal to 2^31 512B sectors can be
>>accepted. Using a zone relative offset in bytes for returning zone append result
>>is OK-ish, but to match the kernel supported range of possible zone size, you
>>need 31+9 bits... 32 does not cut it.
>
>Agree. Our initial assumption was that u32 would cover current zone size
>requirements, but if this is a no-go, we will take the longer path.

Converting to u64 will require a new version of io_uring_cqe, where we
extend at least 32 bits. I believe this will need a whole new allocation
and probably ioctl().

Is this an acceptable change for you? We will of course add support for
liburing when we agree on the right way to do this.

Thanks,
Javier

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