What other possible ways exists to send data from Guest OS to Host Machines ?
I have tried in Qemu:
(1)using vhost-vsock, but it lags in performance.
(2)MMIO callbacks, but it also lags in performance.
Is there any other mechanism by which we can send data from Guest to Host using Qemu ?
You could also try:
TCP socket (via QEMU's emulated networking)
sending via emulated serial port
though these are more "straightforward, easy to do without changing QEMU at all" rather than the necessarily most performant ways.
Broadly for performance you want something where the guest doesn't have to make a lot of MMIO register accesses to transfer a block of data, so anything virtio-based is probably worth looking at -- there are virtio-serial devices, for instance.
Related
I wish I could connect to virtual machines started with QEMU.
Then I should extract the information about the registers (EIP, EBP, etc.)
In XEN for this, there is the function get_vcpu_context, also there are other functions through which you can connect to each virtual machine separately.
Is there any such support for QEMU, and where can I find QEMU hypercalls documentation?
You have a couple of options:
you can connect to the QEMU gdbstub and use the GDB remote protocol to query CPU state. This is probably the most reliable method.
you can connect to the QEMU monitor and use the "info registers" command. Note that the output format of this might change between QEMU releases, though (it is intended for human consumption, not other programs), so it will be less reliable long-term than using GDB remote protocol.
How is it possible to determine the commands to operate a usb device, if that device comes from another operating system and traffic monitoring software cannot be installed on that OS. The only method i can think of is sending random commands to the device, until the device responds, but this seems implausible for more complex commands, and potentially dangerous. For example, consider the DualShock 4 controller. Sony has not made an official driver for this device, so what method can i use to create a linux driver for it?
Get a hardware protocol analyzer. Then you won't need to install any software on the host or device under test. Here is one that I have used:
http://www.totalphase.com/products/beagle-usb12/
I writing a mac application and i need to discover other Macs/PCs/iPhones/iPads connected to the same WIFI network.
Bonjour seems to be the most reasonable choice, but it turned out that it has problems on many types of routers (on mine for example, is not working as it blocks Bonjour services).
I just need to find iPs of devices, then i will try to connect to an application-specific port to determine if my process is running there.
What is the best approach to accomplish this task, without violating the App store Sandboxing?
ARP was the first answer which came to my mind. Does your network-setup allows this?
We have a customized Flash/HTML5 video player we use for users on our site. I'm currently fleshing out the experience for users who have 'suboptimal' bandwidth--basically we'd like the client side code to be able to detect poor user experience due to excessive buffering. I would like to test this "poor bandwidth" handling code in my local development environment.
Does anyone know of good techniques for simulating "poor bandwidth" in a local environment for testing purposes?
More specifically I have my local browser connecting to a virtual machine with instances of uWSGI, nginx, and python/django and I would like to be able to inject arbitrary amounts of delay into the delivery of content from these systems. (I'm primarily concerned with doing this with nginx, which does the video content delivery/streaming).
EDIT: It may be relevant that the dev environment is Mac OS X.
Just use nginx's configuration.
While OS X Lion's Network Link Conditioner works as expected it's still annoying to use when I'm really just trying to test a subset of a web app's behavior--i.e., the slow video buffering handling system.
As such, I've found it much more convenient to set rate limiting in my nginx.conf file, e.g.,:
location ~ /files/(.*\.(mp4|m4v|mov))$ {
...
limit_rate 50k; # <-- Limit download rate per connection to 50kbps
...
}
EDIT: See the nginx HttpCoreModule docs.
FreeBSD is ancestor of Mac OS, so you can use built-in powerful firewall called ipfw.
It can be used in many different cases, for example simulate low bandwidth. Use your own IP address loopback (127.0.0.1) or a remote server (8.8.8.8 in that case).
We do a video interviewing web-application, so I'd like to share with our experience of simulation of bad connection, see example below:
$ sudo su
$ ipfw show
$ ipfw pipe 1 config delay 600ms bw 256kbit/s
$ ipfw add pipe 1 dst-ip 8.8.8.8 dst-port 80
$ ipfw flush
ipfw pipe allows you to simulate slow and unstable connection with using delay, bw and even prob to simulate packet losses.
I just found the Mac OS X Network Link Conditioner but I'm not yet sure it works on loopback, which it would need to for my purposes.
EDIT: This seems to work on loopback, so it seems to solve my problem! This is probably the way to go if you're on OS X 10.7
I'm using this program NetLimiter to simulate "poor bandwidth". It's not free, but have a trial version that works well. Is only for windows :(
Simplified, I have an application where data is intended to flow over the internet between two servers. Ideally, I'd like to test at what point the software ceases to function. At what lowerbound limit (bandwidth, latency, dropped packets) do things stop working to test the reliability of the software.
What I thought I would do was the following:
Setup up 3 machines (VMware instances)
Install the 2 applications on two of the servers.
Setup up the 3rd server to sit between the two machines by doing some sort of magic with Routing and Remote Access on Windows 2003
Install either Traffic Shaper XP or NetLimiter to limit the bandwidth
Run something like TMnetSim Network Simulator to simulate a bad connection.
Does this sound like a good idea or are there easier/better ways of doing this? I'm not that comfortable on Linux and my team mates are even less so.
WANem does exactly this. We have used it both in a virtual machine on the desktop and on a dedicated old pc and it worked great. It can simulate all sorts of broken connectivity.
FreeBSDs ipfw has provisions to simulate links with a given bandwith, latency or error rate. You could use that FreeBSD machine as your machine "in the middle" in your above setup.
You probably can also run at least one of the endpoints on the same machine if you want to reduce the amount of servers involved.
Someone actually packaged up the settings and whatnot necessary for the FreeBSD solution to this problem and they call it DUMMYNET.
It simulates/enforces queue and bandwidth limitations, delays, packet losses, and multipath effects. It also implements a variant of Weighted Fair Queueing called WF2Q+. It can be used on user's workstations, or on FreeBSD machines acting as routers or bridges.
It can simulate exactly what you want, and its free and will boot onto commodity hardware. They even have a canned install of it that is small enough to put on a floppy disk (!) that you can download at that link.
Maybe it is time to learn a bit about Linux because adding a 50ms delay on every outgoing packet can be done in typing just one line:
tc qdisc add dev eth0 root netem delay 50ms
For more see the Linux Traffic Control HOWTO
We had a similar requirement some ten years ago - I'll see if I can recall how we managed it.
If I remember, we wrote a socket proxy program which was controlled by inetd on a UNIX box. This socket would accept connections from a client and open equivalent sessions through to the server. It would then loop, passing messages in both directions.
The way we achieved WAN characteristics was to introduce random delays (with upper and lower limits) in both the connection establishment and the passing of data once the link was up.
It also had the feature to drop the link occasionally as WAN links were less reliable for us than local traffic.
I recall we had to make it threaded to stop the delays from affecting reverse traffic on the link.
There is a very good (and free) Microsoft solution for that, we use it for quite some time and it works great, it can very easily simulate every thing(packet loss, low bandwidth, disconnection, latency....)
This is the best solution i found for a windows environment
More information and a download link can be found here: MARCO blog post
this product has gone some evolution and it is now integrated into visual studio as part of the automation testing, but i found the use of the standalone(that is quite hard to find, so keep a local copy) to work much better. keep in mind that you need at least two computers(or VMs) since you need to pass through a network adapter in order for the application to work its magic.