[PATCH liburing v1 00/12] Introducing t_bind_ephemeral_port() function

[Ammar Faizi]

From: Ammar Faizi <ammarfaizi2@xxxxxxxxxxx>

Hi,

After discussing an intermittent bind() issue with Dylan, I decided to
introduce a new helper function, t_bind_ephemeral_port().

## Problem:
We have many places where we need to bind() a socket to any unused port
number. To achieve that, the current approach does one of the following
mechanisms:

  1) Randomly brute force the port number until the bind() syscall
     succeeds.

  2) Use a static port at compile time (randomly chosen too).

This is not reliable and it results in an intermittent issue (test
fails when the selected port is in use).

## Solution:
Setting @addr->sin_port to zero on a bind() syscall lets the kernel
choose a port number that is not in use. The caller then can know the
port number to be bound by invoking a getsockname() syscall after
bind() succeeds.

Wrap this procedure in a new function called t_bind_ephemeral_port().
The selected port will be returned into @addr->sin_port, the caller
can use it later to connect() or whatever they need.

## Patchset summary:
There are 12 patches in this series, summary:
1) Patch #1 introduces a new helper function t_bind_ephemeral_port().
2) Patch #2 to #6 get rid of the port number brute force mechanism.
3) Patch #7 to #12 stop using a static port number.

Link: https://lore.kernel.org/r/918facd1-78ba-2de7-693a-5f8c65ea2fcd@xxxxxxxxxxx
Cc: Dylan Yudaken <dylany@xxxxxx>
Cc: Facebook Kernel Team <kernel-team@xxxxxx>
Cc: Pavel Begunkov <asml.silence@xxxxxxxxx>
Signed-off-by: Ammar Faizi <ammarfaizi2@xxxxxxxxxxx>
---

Ammar Faizi (12):
  test/helpers: Add `t_bind_ephemeral_port()` function
  t/poll-link: Don't brute force the port number
  t/socket-rw: Don't brute force the port number
  t/socket-rw-eagain: Don't brute force the port number
  t/socket-rw-offset: Don't brute force the port number
  t/files-exit-hang-poll: Don't brute force the port number
  t/socket: Don't use a static port number
  t/connect: Don't use a static port number
  t/shutdown: Don't use a static port number
  t/recv-msgall: Don't use a static port number
  t/232c93d07b74: Don't use a static port number
  t/recv-msgall-stream: Don't use a static port number

 test/232c93d07b74.c         | 10 ++++------
 test/accept.c               |  5 +----
 test/files-exit-hang-poll.c | 23 +++--------------------
 test/helpers.c              | 18 ++++++++++++++++++
 test/helpers.h              |  7 +++++++
 test/poll-link.c            | 20 ++++++--------------
 test/recv-msgall-stream.c   | 22 ++++++++++------------
 test/recv-msgall.c          | 10 ++++------
 test/shutdown.c             |  7 +++----
 test/socket-rw-eagain.c     | 14 ++------------
 test/socket-rw-offset.c     | 13 ++-----------
 test/socket-rw.c            | 13 ++-----------
 test/socket.c               | 11 ++++++-----
 13 files changed, 68 insertions(+), 105 deletions(-)


base-commit: b8c37f02662faa4f2b61840b123201ccc5678fb1
-- 
Ammar Faizi