Signals for file descriptors

Signals for file descriptors

[Anders Melchiorsen]

I am wondering about this commit,

http://git.kernel.org/?p=virt/kvm/kvm-userspace.git;a=commit;h=b4e392c21c4b98c1c13af353caa3d6e6bcb6b8af

which adds signals on tap I/O. It seems a bit half-done to me. For one
thing, it is mixing timers with I/O.

Anyway, my question is about the remaining file descriptors. Should
signals be activated for them as well, for example in
qemu_set_fd_handler2() ? My example on hand is that connecting a VNC
client currently delays until the next timer expiry.


Anders.

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Re: Signals for file descriptors

[Avi Kivity]

Anders Melchiorsen wrote:
> I am wondering about this commit,
>
> http://git.kernel.org/?p=virt/kvm/kvm-userspace.git;a=commit;h=b4e392c21c4b98c1c13af353caa3d6e6bcb6b8af
>
> which adds signals on tap I/O. It seems a bit half-done to me. For one
> thing, it is mixing timers with I/O.
>
>   

The signal handler doesn't actually matter; all that's needed is to 
break out of the loop.

> Anyway, my question is about the remaining file descriptors. Should
> signals be activated for them as well, for example in
> qemu_set_fd_handler2() ? My example on hand is that connecting a VNC
> client currently delays until the next timer expiry.

In practice it doesn't matter, but yes, any fd which we will select() 
needs to have a signal attached.

-- 
Any sufficiently difficult bug is indistinguishable from a feature.


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Re: Signals for file descriptors

[Anders Melchiorsen]

Avi Kivity <avi@qumranet.com> writes:

> In practice it doesn't matter, but yes, any fd which we will
> select() needs to have a signal attached.

It matters to me, because I am removing periodic timers, and so I
ended up where I could not attach with VNC at all (well, strace would
break the loop).

With your answers in mind, I will prepare a patch to add this.


Thanks,
Anders.

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