[RFC,v4,0/3] Add sendto(2) and recvfrom(2) support for io_uring

Message

Ammar Faizi Jan. 7, 2022, midnight UTC

Hello,

This RFC patchset adds sendto(2) and recvfrom(2) support for io_uring.
It also addresses an issue in the liburing GitHub repository [1].


## Motivations
1) By using `sendto()` and `recvfrom()` we can make the submission
   simpler compared to always using `sendmsg()` and `recvmsg()` from
   the userspace.

2) There is a historical patch that tried to add the same
   functionality, but did not end up being applied. [2]

On Tue, 7 Jul 2020 12:29:18 -0600, Jens Axboe <[e-mail]> wrote:
> In a private conversation with the author, a good point was brought
> up that the sendto/recvfrom do not require an allocation of an async
> context, if we need to defer or go async with the request. I think
> that's a major win, to be honest. There are other benefits as well
> (like shorter path), but to me, the async less part is nice and will
> reduce overhead


## Changes summary
There are 3 patches in this series.

PATCH 1/3 renames io_recv to io_recvfrom and io_send to io_sendto.
Note that:

    send(sockfd, buf, len, flags);

  is equivalent to

    sendto(sockfd, buf, len, flags, NULL, 0);

  and

    recv(sockfd, buf, len, flags);

  is equivalent to

    recvfrom(sockfd, buf, len, flags, NULL, NULL);

So it is saner to have `send` and `recv` directed to `sendto` and
`recvfrom` instead of the opposite with respect to the name.

PATCH 2/3 makes `move_addr_to_user()` be a non static function. This
function lives in net/socket.c, we need to call this from io_uring
to add `recvfrom()` support for io_uring. Added net files maintainers
to the CC list.

PATCH 3/3 adds `sendto(2)` and `recvfrom(2)` support for io_uring.
Added two new opcodes: IORING_OP_SENDTO and IORING_OP_RECVFROM.


## How to test
This patchset is based on "for-next" branch in Jens' tree commit:

  c1537fd063e2f1dbd96d8f68b405a66297ee306f ("Merge branch 'for-5.17/drivers' into for-next")

It is also available in the Git repository at:

  https://github.com/ammarfaizi2/linux-block.git ammarfaizi2/linux-block/io_uring-recvfrom-sendto.v4

Test with liburing (added the liburing support, docs, and test program),
the liburing support is based on liburing "master" branch commit:

  918d8061ffdfdf253806a1e8e141c71644e678bd ("Remove getdents support")

It is available in the Git repository at:

  https://github.com/ammarfaizi2/liburing.git sendto-recvfrom.v2

Please review and comment.

---

RFC v4 (this patchset):
  - Rebase the work (sync with "for-next" branch in Jens' tree).

  - Remove Tested-by tag from Nugra as we have changes.

  - (Address Praveen's comment) Zero `sendto_addr_len` and
    `recvfrom_addr_len` on prep when the `req->opcode` is not
    `IORING_OP_{SENDTO,RECVFROM}`.

RFC v3:
  - Fix build error when CONFIG_NET is undefined for PATCH 1/3. I
    tried to fix it in PATCH 3/3, but it should be fixed in PATCH 1/3,
    otherwise it breaks the build in PATCH 1/3.

  - Added `io_uring_prep_{sendto,recvfrom}` docs to the liburing.

RFC v2:
  - Rebase the work, now this patchset is based on commit
    bb3294e22482db4b7ec ("Merge branch 'for-5.17/drivers' into
    for-next").

  - In `io_recvfrom()`, mark the error check of `move_addr_to_user()`
    call as unlikely.

  - Fix build error when CONFIG_NET is undefined.

  - Update liburing test (the branch is still the same, just force
    pushed).

  - Added Nugra to CC list (tester).

---
RFC v3: https://lore.kernel.org/io-uring/[e-mail]/
RFC v2: https://lore.kernel.org/io-uring/[e-mail]/
RFC v1: https://lore.kernel.org/io-uring/[e-mail]/
Link: https://github.com/axboe/liburing/issues/397 [1]
Link: https://lore.kernel.org/io-uring/[e-mail]/ [2]
Signed-off-by: Ammar Faizi <[e-mail]>
---

Ammar Faizi (3):
  io_uring: Rename `io_{send,recv}` to `io_{sendto,recvfrom}`
  net: Make `move_addr_to_user()` be a non static function
  io_uring: Add `sendto(2)` and `recvfrom(2)` support

 fs/io_uring.c                 | 94 +++++++++++++++++++++++++++++++----
 include/linux/socket.h        |  2 +
 include/uapi/linux/io_uring.h |  5 +-
 net/socket.c                  |  4 +-
 4 files changed, 92 insertions(+), 13 deletions(-)


base-commit: c1537fd063e2f1dbd96d8f68b405a66297ee306f