Re: [Qemu-devel] Qemu coroutine behaviour on blocking send(3)

[Stefan Hajnoczi <stefanha@gmail.com>]

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On Fri, Nov 28, 2014 at 01:55:00PM +0700, Iwan Budi Kusnanto wrote:
> I meant, does the coroutine will do yield internally when it get
> blocked on send(3)?

No.  In general, QEMU will use non-blocking file descriptors so the
blocking case does not apply.  (You can't use blocking file descriptors
in an event loop without a risk of blocking the entire event loop.)

There is qemu_co_send(), which attempts the non-blocking send(2) and
yields on EAGAIN.

block/sheepdog.c and nbd.c both use this function.  It's a little ugly
because the caller must add/remove the socket write fd handler function
so that the coroutine is re-entered when the fd becomes writable again.

Stefan

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