1.1 --- a/.rootkeys	Fri Jul 30 13:24:25 2004 +0000
     1.2 +++ b/.rootkeys	Fri Jul 30 13:25:00 2004 +0000
     1.3 @@ -18,6 +18,7 @@ 3f9e7d564bWFB-Czjv1qdmE6o0GqNg docs/inte
     1.4  3f9e7d58t7N6hjjBMxSn-NMxBphchA docs/style.tex
     1.5  410144afnSd2Yw68AHGO5gXu2m3y6A docs/user.tex
     1.6  40d6ccbfKKBq8jE0ula4eHEzBiQuDA docs/xen_config.html
     1.7 +410a4c2bAO_m_l4RsiiPHnZ4ixHWbQ docs/xend.tex
     1.8  3f9e7d5bz8BwYkNuwyiPVu7JJG441A docs/xenstyle.cls
     1.9  3f815144d1vI2777JI-dO4wk49Iw7g extras/mini-os/Makefile
    1.10  3f815144zTnCV5591ulIJQrpe5b-5Q extras/mini-os/README

     2.1 --- /dev/null	Thu Jan 01 00:00:00 1970 +0000
     2.2 +++ b/docs/xend.tex	Fri Jul 30 13:25:00 2004 +0000
     2.3 @@ -0,0 +1,448 @@
     2.4 +% -*- mode: LaTeX -*-
     2.5 +\def\seca{\chapter}
     2.6 +\def\secb{\section}
     2.7 +\def\secc{\subsection}
     2.8 +\def\secd{\subsubsection}
     2.9 +\def\refa{chapter}
    2.10 +\def\refb{section}
    2.11 +\def\refc{section}
    2.12 +\def\refd{section}
    2.13 +
    2.14 +%\def\seca{\section}
    2.15 +%\def\secb{\subsection}
    2.16 +%\def\secc{\subsubsection}
    2.17 +%\def\refa{section}
    2.18 +%\def\refb{section}
    2.19 +%\def\refc{section}
    2.20 +
    2.21 +\documentclass[11pt,twoside,final,openright]{xenstyle}
    2.22 +\usepackage{a4,graphicx,setspace}
    2.23 +\setstretch{1.15}
    2.24 +\input{style.tex}
    2.25 +
    2.26 +\begin{document}
    2.27 +
    2.28 +% TITLE PAGE
    2.29 +\pagestyle{empty}
    2.30 +\begin{center}
    2.31 +\vspace*{\fill}
    2.32 +\includegraphics{eps/xenlogo.eps}
    2.33 +\vfill
    2.34 +\vfill
    2.35 +\vfill
    2.36 +\begin{tabular}{l}
    2.37 +{\Huge \bf Xend} \\[4mm]
    2.38 +{\huge Xen v2.0 for x86} \\[80mm]
    2.39 +
    2.40 +{\Large Xen is Copyright (c) 2004, The Xen Team} \\[3mm]
    2.41 +{\Large University of Cambridge, UK} \\[20mm]
    2.42 +{\large Last updated 30 August 2004}
    2.43 +\end{tabular}
    2.44 +\vfill
    2.45 +\end{center}
    2.46 +\cleardoublepage
    2.47 +
    2.48 +% TABLE OF CONTENTS
    2.49 +\pagestyle{plain}
    2.50 +\pagenumbering{roman}
    2.51 +{ \parskip 0pt plus 1pt
    2.52 +  \tableofcontents }
    2.53 +\cleardoublepage
    2.54 +% PREPARE FOR MAIN TEXT
    2.55 +\pagenumbering{arabic}
    2.56 +\raggedbottom
    2.57 +\widowpenalty=10000
    2.58 +\clubpenalty=10000
    2.59 +\parindent=0pt
    2.60 +\renewcommand{\topfraction}{.8}
    2.61 +\renewcommand{\bottomfraction}{.8}
    2.62 +\renewcommand{\textfraction}{.2}
    2.63 +\renewcommand{\floatpagefraction}{.8}
    2.64 +
    2.65 +\setstretch{1.15}
    2.66 +
    2.67 +\seca{Introduction}
    2.68 +Xend is the control daemon used to manage a machine running the Xen hypervisor.
    2.69 +Xend is responsible for creating and destroying domains and managing their
    2.70 +resources, such as virtual block devices and virtual network interfaces.
    2.71 +
    2.72 +Xend exists because the Xen hypervisor itself only manages the memory image
    2.73 +of a domain and its scheduling. Xen provides the event channels that connect
    2.74 +a domain to its devices, but is intentionally not involved in setting them up.
    2.75 +
    2.76 +Xend runs as a daemon in the privileged domain 0 and uses a low-level api
    2.77 +to communicate with Xen via the domain 0 kernel. Xend exports its control
    2.78 +interface to its clients using HTTP. Most programming languages have
    2.79 +HTTP client libraries, so this interface can be used from most popular 
    2.80 +languages, for example Python, Perl, C, Java.
    2.81 +Xend itself is written in Python, as are most of the Xen tools.
    2.82 +
    2.83 +The xend interface is intended to be a complete interface for the creation
    2.84 +and management of domains. It supports domain creation, shutdown, reboot,
    2.85 +destruction, save, restore and migration.
    2.86 +
    2.87 +When xend creates a domain it creates the domain memory image and communicates
    2.88 +with the device driver domain(s) to configure the devices for the domain.
    2.89 +This sets up connections between the domain and backend device controllers
    2.90 +in the driver domain. When a domain shuts down its memory image cannot be fully released
    2.91 +unless its backend devices are released and disconnected. This is done by xend.
    2.92 +In order to protect against loss of this information when xend is restarted,
    2.93 +xend maintains a persistent database of domain configurations. This allows
    2.94 +xend to be stopped and restarted without loss of configuration information.
    2.95 +For example, in order to upgrade the xend software.
    2.96 +
    2.97 +\seca{Domain lifecycle}
    2.98 +\secb{Domain creation}
    2.99 +Xend is instructed to create a domain by posting a domain\_create message to it,
   2.100 +containing the domain configuration to be instantiated. The domain configuration
   2.101 +is in sxp format and is as far as possible {\em fully-bound}, that is, all
   2.102 +parameters are fully-specified. The domain configuration is saved in the filesystem
   2.103 +so that it can be reused later if necessary.
   2.104 +
   2.105 +The domain configuration specifies the domain name, memory size, kernel image
   2.106 +and parameters, and all the domain devices. Xend uses the Xen api to create
   2.107 +the domain memory image, and then {\em builds} the memory image for the domain
   2.108 +using the kernel image. At this point the domain exists, but it cannot be run because
   2.109 +it has no devices. Xend then communicates with the device driver domain to create
   2.110 +the configured devices. Once the devices are created it sets up event channels
   2.111 +for them between the driver domain and the new domain, and notifies the new domain
   2.112 +that its devices are connected. At this point the domain can be started.
   2.113 +
   2.114 +Xend is also responsible for managing domain consoles. When a domain is created,
   2.115 +xend sets up a console event channel to the domain, and creates a TCP listening port
   2.116 +for the domain console. When a connection is accepted to the port, xend
   2.117 +connects input and output for the port to the domain console channel.
   2.118 +
   2.119 +\secb{Domain destruction}
   2.120 +When a domain terminates, because it has been shutdown or it has crashed, the
   2.121 +domain resources must be released so that the domain memory image can be
   2.122 +finally removed from xen. Xend monitors the domains, and is also signaled by
   2.123 +xen (using a VIRQ) when a domain exits. Xend examines the domain states and
   2.124 +determines which domains have exited. It then communicates with the driver domain
   2.125 +to release the devices for exited domains. Xend also closes any open console
   2.126 +connections and removes the TCP listeners for exited domains.
   2.127 +Once all devices have been released it instructs xen to destroy the memory image.
   2.128 +
   2.129 +\seb{Domain restart}
   2.130 +Domain restart is the xen equivalent of a machine reboot. When a domain
   2.131 +exits because it has been shutdown in reboot mode, its exit code is reboot.
   2.132 +When examining domains to find those that have exited and destroy them,
   2.133 +xend detects those that have exited for reboot and does not completely destroy
   2.134 +them. It disconnects all their devices, and detaches the console listener
   2.135 +from its channel to the domain, but does not close it. Instead it schedules
   2.136 +a call to rebuild the domain from its configuration. This proceeds almost
   2.137 +identically to creating the domain, except that the console listener is
   2.138 +reused and connected to the new domain. This allows existing console
   2.139 +connections to remain connected across a domain restart. The restarted
   2.140 +domain keeps the same name and domain id.
   2.141 +
   2.142 +The determination of when to restart a domain is in fact slightly more
   2.143 +complex than described above. A domain is configured with a 
   2.144 +{\em restart mode}. If the restart mode is {\em onreboot}, the default,
   2.145 +restart happens when the domain is shutdown normally and
   2.146 +exits with code reboot. If the restart mode is {\em never} the domain is
   2.147 +not restarted. If the restart mode is {\em always} the domain is always
   2.148 +restarted, regardless of how it exited.
   2.149 +
   2.150 +In order to prevent continual domain crash causing restart loops, xend
   2.151 +has a {\em minimum restart time}. Xend remembers when a domain was last
   2.152 +restarted and will fail a restart that happens inside the minimum
   2.153 +restart time.
   2.154 +
   2.155 +\seca{Devices}
   2.156 +\secb{Virtual network interfaces}
   2.157 +Each virtual network interface (vif) has 2 parts: the font-end device in its domain,
   2.158 +and the back-end device in the driver domain. Usually the driver domain is domain 0,
   2.159 +and there is a linux network device corresponding to the vif. The linux device for
   2.160 +interface N on domain D is called vifD.N. When a packet is sent on the vif in the 
   2.161 +domain the packet is received from the linux device. The linux devices are connected
   2.162 +to network interfaces using ethernet bridging.
   2.163 +
   2.164 +The default setup is a bridge xen-br0, with eth0 connected to it, and the routes
   2.165 +for eth0 directed at xen-br0. This is controlled by the xend network setup script,
   2.166 +default {\tt /etc/xen/network}, which is run when xend starts.
   2.167 +
   2.168 +When the vifs for a domain are created, a vif control script, default {\tt /etc/xen/vif-bridge},
   2.169 +is run to connect the vif to its bridge. The default script connects the vif
   2.170 +to xen-br0 and optionally sets up iptables rules to prevent IP address spoofing.
   2.171 +The bridge a vif is connected to can be defined in its configuration, and this is useful
   2.172 +for setting up virtual networks using several bridges.
   2.173 +
   2.174 +\secb{Virtual block devices}
   2.175 +Virtual block devices in a domain are interfaces onto back-end device drivers
   2.176 +that export physical devices to domains. In the default configuration the back-end
   2.177 +driver is in domain 0 and can export any linux block device to a domain. This includes
   2.178 +physical disk partitions, LVM volumes and loopback mounts of files. In fact anything
   2.179 +that linux can represent as a block device can be exported to a domain as virtual
   2.180 +block device.
   2.181 +
   2.182 +\seca{Xend invocation}
   2.183 +Xend is started (by root) using the command
   2.184 +\begin{verbatim}
   2.185 +xend start
   2.186 +\end{verbatim}
   2.187 +Xend can be stopped using
   2.188 +\begin{verbatim}
   2.189 +xend stop
   2.190 +\end{verbatim}
   2.191 +Xend must be started before any domains (apart from domain 0) can be created.
   2.192 +If you try to use the {\tt xm} tool when xend is not running you will get a
   2.193 +'connection refused' message.
   2.194 +
   2.195 +\secb{Xend configuration}
   2.196 +Xend reads its own configuration from {\tt /etc/xen/xend-config.sxp}, which is
   2.197 +a sequence of s-expressions. The configuration parameters are:
   2.198 +\begin{itemize}
   2.199 +
   2.200 +\item xend-port: Port xend should use for the HTTP interface (default 8000).
   2.201 +
   2.202 +\item xend-address: Address xend should listen on.
   2.203 +  Specifying 'localhost' prevents remote connections.
   2.204 +  Specifying the empty string '' allows all connections, and is the default.
   2.205 +
   2.206 +\item network-script: The script used to start/stop networking for xend (default network).
   2.207 +
   2.208 +\item vif-bridge: The default bridge that virtual interfaces should be connected to
   2.209 +  (default xen-br0).
   2.210 +
   2.211 +\item vif-script: The default script used to control virtual interfaces
   2.212 +  (default vif-bridge).
   2.213 +
   2.214 +\item vif-antispoof: Whether iptables should be set up to prevent IP spoofing for
   2.215 +  virtual interfaces (default yes).
   2.216 +\end{itemize}
   2.217 +
   2.218 +Configuration scripts ({\it e.g.} for network-script) are looked for in {\tt /etc/xen}
   2.219 +unless their name begins with '/'.
   2.220 +
   2.221 +Xend sends its log output to {\tt /var/log/xend.log}. This is a rotating logfile,
   2.222 +and logs are moved onto {\tt xend.log.1} {\it etc.} as they get large. Old logs may
   2.223 +be deleted.
   2.224 +
   2.225 +\secb{Xend database}
   2.226 +Xend needs to make some data persistent, and it uses files under {\tt /var/xen/xend-db}
   2.227 +for this. The persistent data is stored in files in SXP format. Domain information
   2.228 +is saved when domains are created. When xend starts it reads the file {\tt /var/xen/lastboot}
   2.229 +(if it exists) to determine the last time the system was rebooted. It compares this time
   2.230 +with the last reboot time in {\tt wtmp} to determine if the system has been rebooted
   2.231 +since xend last ran. If the system has been rebooted xend removes all its saved data
   2.232 +that is not persistent across reboots (for example domain data).
   2.233 +
   2.234 +\seca{Xend HTTP Interface}
   2.235 + The xend interface uses HTTP 1.1 \cite{http} as its transport.
   2.236 +Simple PUT and GET calls can encode parameters using the standard url-encoding 
   2.237 +for parameters: MIME type {\tt application/x-www-form-urlencoded}.
   2.238 +When file upload is required, the {\tt multipart/form-data} encoding is used.
   2.239 +See the HTML 4.1 specification for details \cite{html}.
   2.240 +
   2.241 +Xend functions as a webserver and supports two interfaces: one
   2.242 +for web-browsers and one for programs.
   2.243 +The web-browser interface returns replies in HTML and includes forms
   2.244 +for interactive operations such as stopping domains and creating domains
   2.245 +from an uploaded configuration. The programmatic interface usually returns replies
   2.246 +in s-expression format. Both interfaces are accessed
   2.247 +in exactly the same way over HTTP - the only difference is the data returned.
   2.248 +
   2.249 +The webserver distinguishes browsers from programs using the {\tt User-Agent}
   2.250 +and {\tt Accept} headers in the HTTP request. If there is no {\tt User-Agent} or no
   2.251 +{\tt Acccept} header, or {\tt Accept} includes the type {\tt application/sxp}, the
   2.252 +webserver assumes the client is a program and returns SXP. Otherwise
   2.253 +it assumes the client is a webserver and returns HTML.
   2.254 +In some cases the return value is essentially a string, so {\tt Content-Type}
   2.255 +{\tt text/plain} is returned.
   2.256 +
   2.257 +The HTTP api supported is listed below. All paths in it are relative to the
   2.258 +server root, for example {\tt http://localhost:8000/xend}.
   2.259 +As defined in the HTTP specification, we use GET for side-effect free
   2.260 +operations that may safely be repeated, and POST for operations with
   2.261 +side-effects. For each request we list the HTTP method (GET or POST),
   2.262 +the url relative to the server root, the operation name and arguments (if any).
   2.263 +The operation name is passed as request parameter 'op', and the arguments
   2.264 +are passed by name. Operation name and parameters can be encoded using either
   2.265 +encoding described above. We also list the corresponding api function from the
   2.266 +Python client interface in {\tt xen.xend.XendClient}.
   2.267 +
   2.268 +\begin{itemize}
   2.269 +\item {\tt GET /},\\
   2.270 +  {\tt xend()}:\\
   2.271 +  Get list of urls under xend root.
   2.272 +
   2.273 +\item {\tt GET /node},\\
   2.274 +  {\tt xend\_node()}:\\
   2.275 +  Get node information.
   2.276 +
   2.277 +\item {\tt POST /node shutdown()},\\
   2.278 +  {\tt xend\_node\_shutdown()}:\\
   2.279 +  Shutdown the node
   2.280 +
   2.281 +\item {\tt POST /node reboot()},\\
   2.282 +  {\tt xend\_node\_reboot()}:\\
   2.283 +  Reboot the node
   2.284 +
   2.285 +\item {\tt POST /node notify()}:\\
   2.286 +  Set node notification url
   2.287 +  
   2.288 +\item {\tt GET /node/dmesg},\\
   2.289 +  {\tt xend\_node\_dmesg()}:\\
   2.290 +  Get xen boot message.
   2.291 +
   2.292 +\item {\tt GET /node/log},\\
   2.293 +  {\tt xend\_node\_log()}:\\
   2.294 +  Get xend log.
   2.295 +
   2.296 +\item {\tt GET /domain}\\
   2.297 +  {\tt xend\_domains()}:\\
   2.298 +  Get list of domains.
   2.299 +
   2.300 +\item {\tt POST /domain create(config)},\\
   2.301 +  {\tt xend\_domain\_create(config)}:\\
   2.302 +  Create a domain.
   2.303 +
   2.304 +\item {\tt POST /domain restore(file)},\\
   2.305 +  {\tt xend\_domain\_restore(filename)}:\\
   2.306 +  Restore a saved domain.
   2.307 +
   2.308 +\item {\tt GET /domain/<dom>},\\
   2.309 +  {\tt xend\_domain(dom)}:\\
   2.310 +  Get domain information.
   2.311 +
   2.312 +\item {\tt POST /domain/[dom] configure(config)},\\
   2.313 +  {\tt xend\_domain\_configure(dom, conf)}:\\
   2.314 +  Configure an existing domain (for internal use by restore and migrate).
   2.315 +
   2.316 +\item {\tt POST /domain/[dom] unpause()},\\
   2.317 +  {\tt xend\_domain\_unpause(dom)}:\\
   2.318 +  Start domain running
   2.319 +
   2.320 +\item {\tt POST /domain/[dom] pause()},\\
   2.321 +  {\tt xend\_domain\_pause(dom)}:\\
   2.322 +  Stop domain running.
   2.323 +
   2.324 +\item {\tt POST /domain/[dom] shutdown(reason)},\\
   2.325 +  {\tt xend\_domain\_shutdown(dom, reason)}:\\
   2.326 +  Shutdown domain, reason can be reboot, poweroff, halt.
   2.327 +
   2.328 +\item {\tt POST /domain/[dom] destroy(reason)},\\
   2.329 +  {\tt xend\_domain\_destroy(dom, reason)}:\\
   2.330 +  Destroy domain, reason can be reboot, halt.
   2.331 +
   2.332 +\item {\tt POST /domain/[dom] save(file)},\\
   2.333 +  {\tt xend\_domain\_save(dom, filename)}:\\
   2.334 +  Save a domain to a file.
   2.335 +
   2.336 +\item {\tt POST /domain/[dom] migrate(dst)},\\
   2.337 +  {\tt xend\_domain\_migrate(dom, dst)}:\\
   2.338 +  Migrate a domain.
   2.339 +
   2.340 +\item {\tt POST /domain/[dom] pincpu(cpu)},\\
   2.341 +  {\tt xend\_domain\_pincpu(self, id, cpu)}\\:
   2.342 +  Pin a domain to a cpu.
   2.343 +
   2.344 +\item {\tt POST /domain/[dom] bvt\_set(mcuadv, warp, warpl, warpu)},\\
   2.345 +  {\tt xend\_domain\_cpu\_bvt\_set(dom, mcuadv, warp, warpl, warpu)}:\\
   2.346 +  Set BVT scheduler parameters.
   2.347 +
   2.348 +\item {\tt POST /domain/[dom] fbvt\_set(mcuadv, warp, warpl, warpu)},\\
   2.349 +  {\tt xend\_domain\_cpu\_fbvt\_set(dom, mcuadv, warp, warpl, warpu)}:\\
   2.350 +  Set FBVT scheduler parameters.
   2.351 +
   2.352 +\item {\tt POST /domain/[dom] atropos\_set(period, slice, latency, xtratime)},\\
   2.353 +  {\tt xend\_domain\_cpu\_atropos\_set(dom, period, slice, latency, xtratime)}:\\
   2.354 +  Set atropos scheduler parameters.
   2.355 +
   2.356 +\item {\tt POST /domain/[dom] maxmem\_set(memory)},\\
   2.357 +  {\tt xend\_domain\_maxmem\_set(dom, memory)}:\\
   2.358 +  Set domain maximum memory limit.
   2.359 +
   2.360 +\item {\tt POST /domain/[dom] device\_create(config)}\\
   2.361 +  {\tt xend\_domain\_device\_create(dom, config)}:\\
   2.362 +  Add a device to a domain.
   2.363 +
   2.364 +\item {\tt POST /domain/[dom] device\_destroy(type, index)},\\
   2.365 +  {\tt xend\_domain\_device\_destroy(dom, type, index)}:\\
   2.366 +  Delete a device from a domain
   2.367 +
   2.368 +\item {\tt GET /domain/[dom] vifs()},\\
   2.369 +  {\tt xend\_domain\_vifs(dom)}:\\
   2.370 +  Get virtual network interfaces.
   2.371 +
   2.372 +\item {\tt GET /domain/[dom] vif(vif)},\\
   2.373 +  {\tt xend\_domain\_vif(dom, vif)}:\\
   2.374 +  Get virtual network interface.
   2.375 +
   2.376 +\item {\tt GET /domain/[dom] vbds()},\\
   2.377 +  {\tt xend\_domain\_vbds(dom)}:\\
   2.378 +  Get virtual block devices.
   2.379 +
   2.380 +\item {\tt GET /domain/[dom] vbd(vbd)},\\
   2.381 +  {\tt xend\_domain\_vbd(dom, vbd)}:\\
   2.382 +  Get virtual block device.
   2.383 +
   2.384 +\item {\tt GET /console},\\
   2.385 +  {\tt xend\_consoles()}:\\
   2.386 +  Get list of consoles.
   2.387 +
   2.388 +\item {\tt GET /console/[id]}\\
   2.389 +  {\tt xend\_console(id)}:\\
   2.390 +  Get information about a console.
   2.391 +
   2.392 +\item {\tt GET /console/[id] disconnect()}\\
   2.393 +  {\tt xend\_console\_disconnect(self, id)}:\\
   2.394 +  Disconnect any console TCP connection.
   2.395 +
   2.396 +\item {\tt GET /vnet}\\
   2.397 +  {\tt xend\_vnets()}:\\
   2.398 +  Get list of vnets (virtual networks).
   2.399 +
   2.400 +\item {\tt GET /vnet/[id]}\\
   2.401 +  {\tt xend\_vnet(id)}:\\
   2.402 +  Get information about a virtual network.
   2.403 +
   2.404 +\item {\tt POST /vnet create(config)}\\
   2.405 +  {\tt xend\_vnet\_create(conf)}:\\
   2.406 +  Create a vnet.
   2.407 +
   2.408 +\item {\tt POST /vnet/[id] delete()}\\
   2.409 +  {\tt xend\_vnet\_delete(id)}:\\
   2.410 +  Delete a vnet.
   2.411 +
   2.412 +\item {\tt POST /event inject(event)}\\
   2.413 +  {\tt xend\_event\_inject(sxpr)}:\\
   2.414 +  Inject an event.
   2.415 +
   2.416 +\end{itemize}
   2.417 +
   2.418 +\secb{Xend debugging interface}
   2.419 +Xend also listens on port 8001. Connecting to this port (for example via telnet)
   2.420 +allows access to some debugging functions:
   2.421 +\begin{itemize}
   2.422 +\item help: list functions
   2.423 +\item traceon: turn xend tracing on
   2.424 +\item traceoff: turn xend tracing off
   2.425 +\item quit: disconnect.
   2.426 +\item info: list console listeners, block and network device controllers.
   2.427 +\end{itemize}
   2.428 +
   2.429 +When tracing is on xend logs all functions calls and exceptions to
   2.430 +{\tt /var/log/xend.trace}.
   2.431 +
   2.432 +\begin{thebibliography}{99}
   2.433 +
   2.434 +\bibitem{html}
   2.435 +HTML 4.01 Specification,\\
   2.436 +http://www.w3.org/TR/html4/,\\
   2.437 +W3C Recommendation, 24 December 1999.
   2.438 +
   2.439 +\bibitem{http}
   2.440 +Hypertext Transfer Protocol -- HTTP/1.1,\\
   2.441 +http://www.ietf.org/rfc/rfc2616.txt,\\
   2.442 +RFC 2616, IETF 1999.
   2.443 +
   2.444 +\bibitem{ssh}
   2.445 +http://www.openssh.org.
   2.446 +
   2.447 +\bibitem{stunnel}
   2.448 +http://www.stunnel.org.
   2.449 +
   2.450 +\end{thebibliography}
   2.451 +\end{document}
   2.452 \ No newline at end of file