[Qemu-devel] [PATCH v2 0/9] main-loop: switch to g_poll(3) on POSIX hosts

[Stefan Hajnoczi <stefanha@redhat.com>]

Amos Kong <akong@redhat.com> reported that file descriptors numbered higher
than 1024 could crash QEMU.  This is due to the fixed size of the fd_set type
used for select(2) event polling.

This series converts the main-loop.c and aio-posix.c select(2) calls to
g_poll(3).  This eliminates the fd_set type and allows QEMU to scale to high
numbers of file descriptors.

The g_poll(3) interface is a portable version of the poll(2) system call.  The
difference to select(2) is that fine-grained events (G_IO_IN, G_IO_OUT,
G_IO_HUP, G_IO_ERR, G_IO_PRI) can be monitored instead of just
read/write/exception.  Also, there is no limit to the file descriptor numbers
that may be used, allowing applications to scale to many file descriptors.  See
the documentation for details:

  http://developer.gnome.org/glib/2.28/glib-The-Main-Event-Loop.html#g-poll

The QEMU main loop works as follows today:

1. Call out to slirp, iohandlers, and glib sources to fill rfds/wfds/xfds with
   the file descriptors to select(2).
2. Perform the select(2) call.
3. Call out to slirp, iohandlers, and glib sources to handle events polled in
   rfds/wfds/xfds.

The plan of attack is as follows:

1. Replace select(2) with g_poll(3).  Use glue that converts between
   rfds/wfds/xfds and GPollFD so that the unconverted QEMU components still
   work.

2. Convert slirp, iohandlers, and glib source fill/poll functions to use
   GPollFD directly instead of rfds/wfds/xfds.

3. Drop the glue since all components now natively use GPollFD.

4. Convert aio-posix.c to g_poll(3) by reusing GPollFD.

I have tested that the series builds and is bisectable on Linux and Windows
hosts.  But I have not done extensive testing on other host platforms or with
long-term guests to check for performance regressions.

v2:
 * Replace custom Poller type with GArray [aliguori]

Stefan Hajnoczi (9):
  main-loop: fix select_ret uninitialized variable warning
  main-loop: switch to g_poll() on POSIX hosts
  main-loop: switch POSIX glib integration to GPollFD
  slirp: switch to GPollFD
  iohandler: switch to GPollFD
  main-loop: drop rfds/wfds/xfds for good
  aio: extract aio_dispatch() from aio_poll()
  aio: convert aio_poll() to g_poll(3)
  aio: support G_IO_HUP and G_IO_ERR

 aio-posix.c              | 130 ++++++++++++++++++---------------------
 async.c                  |   2 +
 include/block/aio.h      |   3 +
 include/qemu/main-loop.h |   4 +-
 iohandler.c              |  40 +++++++++---
 main-loop.c              | 156 ++++++++++++++++++++++++++---------------------
 slirp/libslirp.h         |   6 +-
 slirp/main.h             |   1 -
 slirp/slirp.c            | 136 ++++++++++++++++++++++++-----------------
 slirp/socket.c           |   9 ---
 slirp/socket.h           |   2 +
 stubs/slirp.c            |   6 +-
 12 files changed, 270 insertions(+), 225 deletions(-)

-- 
1.8.1