Hello,
(This series is based on the previous series that I've sent out for
virtio-serial).
This patch series adds fixes for the chardev interface to let callers
of qemu_chr_write() know how many bytes were sent and how many are
unsent in case of errors.
In case of EAGAIN, the unix_write() function just kept spinning while
attempting to write to the chardev till it succeeded. This resulted in
a stuck VM in case a chardev had opened connection but wasn't reading
anything from qemu.
There are two fixes for that case:
- Poll for POLLOUT instead of directly attempting write(), which helps
relax the CPU (and we become greener).
- If the file that we're writing to is nonblocking, return -EAGAIN to
the caller of qemu_chr_write() so that appropriate actions can be
taken higher up in the stack. This is done when POLLOUT doesn't get
set in a 10-ms timeout that's specified to poll.
Using these changes, the virtio-console code is modified to handle
slow remote connections by letting the virtio-serial-bus code know of
the traffic jam and throttle the port.
I've tested this with my auto-virtserial testsuite to check for data
sent from guest to a host socket. Throttling works fine.
Comments?
Amit Shah (5):
char: Let the caller know how many bytes were written in case of
incomplete writes
char: unix write: Add some sleep to ease off spinning in a tight loop
char: unix: For files that are nonblocking, report -EAGAIN to calling
functions
virtio-console: Factor out common init between console and generic
ports
virtio-console: Throttle virtio-serial-bus if we can't consume any
more guest data
console.c | 10 ++--
gdbstub.c | 15 +++--
hw/bt-hci-csr.c | 8 ++--
hw/debugcon.c | 5 +-
hw/msmouse.c | 5 +-
hw/parallel.c | 5 ++-
hw/serial.c | 4 +-
hw/usb-serial.c | 4 +-
hw/virtio-console.c | 146 ++++++++++++++++++++++++++++++++++++++++++++------
monitor.c | 4 +-
net/socket.c | 7 ++-
qemu-char.c | 125 ++++++++++++++++++++++++++++++--------------
qemu-char.h | 7 ++-
qemu_socket.h | 2 +-
slirp/slirp.c | 12 +++--
15 files changed, 268 insertions(+), 91 deletions(-)
