Re: [Qemu-devel] [PATCH v2 1/5] backdoor: Add documentation

[Anthony Liguori <anthony@codemonkey.ws>]

On 12/05/2011 04:22 PM, Lluís Vilanova wrote:
> Signed-off-by: Lluís Vilanova<vilanova@ac.upc.edu>
> ---
>   docs/backdoor.txt |  167 +++++++++++++++++++++++++++++++++++++++++++++++++++++
>   1 files changed, 167 insertions(+), 0 deletions(-)
>   create mode 100644 docs/backdoor.txt
>
> diff --git a/docs/backdoor.txt b/docs/backdoor.txt
> new file mode 100644
> index 0000000..1c6502a
> --- /dev/null
> +++ b/docs/backdoor.txt
> @@ -0,0 +1,167 @@
> += Backdoor communication channel =
> +
> +== Introduction ==
> +
> +This document describes how the guest can use the backdoor communication channel
> +to interact with user-provided code inside QEMU.
> +
> +The backdoor provides a lightweight and guest-initiated communication channel
> +between code running inside the guest system and code in QEMU, including both
> +QEMU in 'softmmu' and 'user' modes.
> +
> +The semantics of the backdoor channel are up to the user, who must provide the
> +implementation of the QEMU-side callbacks used when the backdoor channel is
> +invoked.
> +
> +On the guest side, code can be linked against a simple library provided in QEMU
> +to interface with the backdoor channel.
> +
> +The features of this mechanism are:
> +
> +* Minimal setup for the guest.
> +* Independent of guest architecture.
> +* Works with 'softmmu' and 'user' mode.
> +* Negligible guest overhead; guest invocations of the backdoor channel does not
> +  go through any OS abstraction, except during the setup of the communication
> +  channel.
> +* Negligible host overhead; invocations of the backdoor channel are interpreted
> +  by QEMU, while a side-channel can be used as regular memory to communicate
> +  bulk data without any extra overhead.
> +* The user-provided backdoor callbacks can perform arbitrary actions on the
> +  guest system (e.g., read or write memory, change register values, etc.).
> +
> +
> +== QEMU-side code ==
> +
> +1. Create the "Makefile" to build the user-provided backdoor channel library:
> +
> +    mkdir /tmp/my-backdoor-qemu
> +    cat>  /tmp/my-backdoor-qemu/Makefile<<EOF
> +    include $(BUILD_DIR)/config-host.mak
> +    include $(BUILD_DIR)/$(TARGET_DIR)../config-target.mak
> +    include $(SRC_PATH)/rules.mak
> +
> +    vpath %.c /tmp/my-backdoor-qemu
> +
> +
> +    libbackdoor.a: backdoor.o
> +
> +
> +    # Include automatically generated dependency files
> +    -include $(wildcard *.d)
> +    EOF
> +
> +2. Implement the callbacks declared in "backdoor/qemu/qemu-backdoor.h":
> +
> +    cat>  /tmp/my-backdoor-qemu/backdoor.c<<EOF

Oh, I didn't see this.

Major Nack on this.  This is not reasonable at all to do.  We're not sneaking in 
an ad-hoc plugin interface here.

Regards,

Anthony Liguori