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Date:   Mon, 20 Jul 2020 18:14:16 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     Kanchan Joshi <joshiiitr@gmail.com>
Cc:     Christoph Hellwig <hch@infradead.org>,
        Jens Axboe <axboe@kernel.dk>,
        Kanchan Joshi <joshi.k@samsung.com>, viro@zeniv.linux.org.uk,
        bcrl@kvack.org, Damien.LeMoal@wdc.com, asml.silence@gmail.com,
        linux-fsdevel@vger.kernel.org, Matias Bj??rling <mb@lightnvm.io>,
        linux-kernel@vger.kernel.org, linux-aio@kvack.org,
        io-uring@vger.kernel.org, linux-block@vger.kernel.org,
        Selvakumar S <selvakuma.s1@samsung.com>,
        Nitesh Shetty <nj.shetty@samsung.com>,
        Javier Gonzalez <javier.gonz@samsung.com>
Subject: Re: [PATCH v3 4/4] io_uring: add support for zone-append
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On Mon, Jul 20, 2020 at 10:19:57PM +0530, Kanchan Joshi wrote:
> On Fri, Jul 10, 2020 at 7:41 PM Kanchan Joshi <joshiiitr@gmail.com> wrote:
> > If we are doing this for zone-append (and not general cases), "__s64
> > res64" should work -.
> > 64 bits = 1 (sign) + 23 (bytes-copied: cqe->res) + 40
> > (written-location: chunk_sector bytes limit)

No, don't do this.

 struct io_uring_cqe {
	__u64   user_data;      /* sqe->data submission passed back */
-	__s32   res;            /* result code for this event */
-	__u32   flags;
+	union {
+		struct {
+			__s32   res;    /* result code for this event */
+			__u32   flags;
+		};
+		__s64		res64;
+	};
 };

Return the value in bytes in res64, or a negative errno.  Done.
			
>   * IO completion data structure (Completion Queue Entry)
>   */
>  struct io_uring_cqe {
> -       __u64   user_data;      /* sqe->data submission passed back */
> -       __s32   res;            /* result code for this event */
> -       __u32   flags;
> +       __u64   user_data;      /* sqe->data submission passed back */
> +        union {
> +                struct {
> +                        __s32   res;            /* result code for
> this event */
> +                        __u32   flags;
> +                };
> +               /* Alternate for zone-append */
> +               struct {
> +                       union {
> +                               /*
> +                                * kernel uses this to store append result
> +                                * Most significant 23 bits to return number of
> +                                * bytes or error, and least significant 41 bits
> +                                * to return zone-relative offset in bytes
> +                                * */
> +                               __s64 res64;
> +                               /*for user-space ease, kernel does not use*/
> +                               struct {
> +#if defined(__LITTLE_ENDIAN_BITFIELD)
> +                                       __u64 append_offset :
> APPEND_OFFSET_BITS;
> +                                       __s32 append_res : APPEND_RES_BITS;
> +#elif defined(__BIG_ENDIAN_BITFIELD)
> +                                       __s32 append_res : APPEND_RES_BITS;
> +                                       __u64 append_offset :
> APPEND_OFFSET_BITS;
> +#endif
> +                               }__attribute__ ((__packed__));
> +                       };
> +                };
> +        };
>  };
> 
> -- 
> Joshi