Re: [PATCH 5/5] ioeventfd: Introduce KVM_IOEVENTFD_FLAG_SOCKET

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Jul 06, 2011 at 07:37:58AM +0300, Sasha Levin wrote:
> The new flag allows passing a connected socket instead of an
> eventfd to be notified of writes or reads to the specified memory region.
> 
> Instead of signaling an event, On write - the value written to the memory
> region is written to the pipe.
> On read - a notification of the read is sent to the host, and a response
> is expected with the value to be 'read'.
> 
> Using a socket instead of an eventfd is usefull when any value can be
> written to the memory region but we're interested in recieving the
> actual value instead of just a notification.
> 
> A simple example for practical use is the serial port. we are not
> interested in an exit every time a char is written to the port, but
> we do need to know what was written so we could handle it on the guest.
> 
> Cc: Avi Kivity <avi@redhat.com>
> Cc: Ingo Molnar <mingo@elte.hu>
> Cc: Marcelo Tosatti <mtosatti@redhat.com>
> Cc: Michael S. Tsirkin <mst@redhat.com>
> Cc: Pekka Enberg <penberg@kernel.org>
> Signed-off-by: Sasha Levin <levinsasha928@gmail.com>
> ---
>  Documentation/virtual/kvm/api.txt |   18 ++++-
>  include/linux/kvm.h               |    9 ++
>  virt/kvm/eventfd.c                |  153 ++++++++++++++++++++++++++++++++-----
>  3 files changed, 161 insertions(+), 19 deletions(-)
> 
> diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
> index 317d86a..74f0946 100644
> --- a/Documentation/virtual/kvm/api.txt
> +++ b/Documentation/virtual/kvm/api.txt
> @@ -1330,7 +1330,7 @@ Returns: 0 on success, !0 on error
>  
>  This ioctl attaches or detaches an ioeventfd to a legal pio/mmio address
>  within the guest.  A guest write in the registered address will signal the
> -provided event instead of triggering an exit.
> +provided event or write to the provided socket instead of triggering an exit.
>  
>  struct kvm_ioeventfd {
>  	__u64 datamatch;
> @@ -1341,6 +1341,13 @@ struct kvm_ioeventfd {
>  	__u8  pad[36];
>  };
>  
> +struct kvm_ioeventfd_data {
> +	__u64 data;
> +	__u64 addr;
> +	__u32 len;
> +	__u8  is_write;
> +};
> +
>  The following flags are defined:
>  
>  #define KVM_IOEVENTFD_FLAG_DATAMATCH (1 << kvm_ioeventfd_flag_nr_datamatch)
> @@ -1348,6 +1355,7 @@ The following flags are defined:
>  #define KVM_IOEVENTFD_FLAG_DEASSIGN  (1 << kvm_ioeventfd_flag_nr_deassign)
>  #define KVM_IOEVENTFD_FLAG_READ      (1 << kvm_ioeventfd_flag_nr_read)
>  #define KVM_IOEVENTFD_FLAG_NOWRITE   (1 << kvm_ioeventfd_flag_nr_nowrite)
> +#define KVM_IOEVENTFD_FLAG_SOCKET    (1 << kvm_ioeventfd_flag_nr_socket)
>  
>  If datamatch flag is set, the event will be signaled only if the written value
>  to the registered address is equal to datamatch in struct kvm_ioeventfd.
> @@ -1359,6 +1367,14 @@ passed in datamatch.
>  If the nowrite flag is set, the event won't be signaled when the specified address
>  is being written to.
>  
> +If the socket flag is set, fd is expected to be a connected AF_UNIX
> +SOCK_SEQPACKET socket.

Let's verify that then?

> +
> +	if (p->sock)
> +		socket_write(p->sock, &data, sizeof(data));
> +	else
> +		eventfd_signal(p->eventfd, 1);
> +
>  	return 0;
>  }

This still loses the data if socket would block and there's a signal.
I think we agreed to use non blocking operations and exit to
userspace in that case?


>  
> @@ -534,6 +607,7 @@ ioeventfd_read(struct kvm_io_device *this, gpa_t addr, int len,
>  		void *val)
>  {
>  	struct _ioeventfd *p = to_ioeventfd(this);
> +	struct kvm_ioeventfd_data data;
>  
>  	/* Exit if signaling on reads isn't requested */
>  	if (!p->track_reads)
> @@ -542,7 +616,21 @@ ioeventfd_read(struct kvm_io_device *this, gpa_t addr, int len,
>  	if (!ioeventfd_in_range(p, addr, len, val))
>  		return -EOPNOTSUPP;
>  
> -	eventfd_signal(p->eventfd, 1);
> +	data = (struct kvm_ioeventfd_data) {
> +		.addr = addr,
> +		.len = len,
> +		.is_write = 0,
> +	};
> +
> +	if (p->sock) {
> +		socket_write(p->sock, &data, sizeof(data));
> +		socket_read(p->sock, &data, sizeof(data));
> +		set_val(val, len, data.data);

Same here.

> +	} else {
> +		set_val(val, len, p->datamatch);
> +		eventfd_signal(p->eventfd, 1);
> +	}
> +
>  	return 0;
>  }
>


-- 
MST