Re: [PATCH v3 4/4] io_uring: add support for zone-append

Matthew Wilcox
2020-07-20T17:14:31Z

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