[RFC,0/3] introduce coroutine library

  This patchset introduces the coroutine library which will help refactor
the hns3 PMD's reset process.

The hns3 single function reset process consists of the following steps:
    1.stop_service();
    2.prepare_reset();
    3.delay(100ms);
    4.notify_hw();
    5.wait_hw_reset_done(); // multiple sleep waits are involved.
    6.reinit();
    7.restore_conf();

If the DPDK process take over multiple hns3 functions (e.g. 100),
it's impractical to reset and restore functions in sequence:
    1.proc_func(001); // will completed in 100+ms range.
    2.proc_func(002); // will completed in 100~200+ms range.
    ...
    x.proc_func(100); // will completed in 9900~10000+ms range.
The later functions will process fail because it's too late to deal with.

One solution is that create a reset thread for each function, and it
will lead to large number of threads if the DPDK process take over
multiple hns3 functions.

So the current hns3 driver uses asynchronous mechanism, for examples, it
use rte_eal_alarm_set() when process delay(100ms), it splits a serial
process into multiple asynchronous processes, and the code is complex
and difficult to understand.

The coroutine is a good mechanism to provide programmers with the 
simplicity of keeping serial processes within a limited number of
threads.

This patchset use <ucontext.h> to build the coroutine framework, and it
just provides a demo. More APIs maybe added in the future.

In addition, we would like to ask the community whether it it possible
to accept the library. If not, whether it is allowed to provide the
library in hns3 PMD.

Chengwen Feng (3):
  lib/coroutine: add coroutine library
  examples/coroutine: support coroutine examples
  net/hns3: refactor reset process with coroutine

 drivers/net/hns3/hns3_ethdev.c    | 217 ++++++++++++++++++++++++++++++
 drivers/net/hns3/hns3_ethdev.h    |   3 +
 drivers/net/hns3/hns3_intr.c      |  38 ++++++
 drivers/net/hns3/meson.build      |   2 +-
 examples/coroutine/main.c         | 153 +++++++++++++++++++++
 examples/coroutine/meson.build    |  10 ++
 examples/meson.build              |   1 +
 lib/coroutine/meson.build         |   8 ++
 lib/coroutine/rte_coroutine.c     | 190 ++++++++++++++++++++++++++
 lib/coroutine/rte_coroutine.h     | 110 +++++++++++++++
 lib/coroutine/rte_coroutine_imp.h |  46 +++++++
 lib/coroutine/version.map         |  11 ++
 lib/meson.build                   |   1 +
 13 files changed, 789 insertions(+), 1 deletion(-)
 create mode 100644 examples/coroutine/main.c
 create mode 100644 examples/coroutine/meson.build
 create mode 100644 lib/coroutine/meson.build
 create mode 100644 lib/coroutine/rte_coroutine.c
 create mode 100644 lib/coroutine/rte_coroutine.h
 create mode 100644 lib/coroutine/rte_coroutine_imp.h
 create mode 100644 lib/coroutine/version.map