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diff --git a/hurd/documentation/hurd-talk.html b/hurd/documentation/hurd-talk.html deleted file mode 100644 index 29518dd6..00000000 --- a/hurd/documentation/hurd-talk.html +++ /dev/null @@ -1,1061 +0,0 @@ -[[!meta copyright="Copyright © 2001 Marcus Brinkmann"]] - -[[!meta license="Verbatim copying and distribution of this entire article is -permitted in any medium, provided this notice is preserved."]] - -[[!meta title="The Hurd, a presentation by Marcus Brinkmann"]] - - -<H4><A NAME="contents">Table of Contents</A></H4> -<UL> - <LI><A HREF="#int" NAME="TOCint">Introduction</A> - <LI><A HREF="#ove" NAME="TOCove">Overview</A> - <LI><A HREF="#his" NAME="TOChis">Historicals</A> - <LI><A HREF="#ker" NAME="TOCker">Kernel Architectures</A> - <LI><A HREF="#mic" NAME="TOCmic">Micro vs Monolithic</A> - <LI><A HREF="#sin" NAME="TOCsin">Single Server vs Multi Server</A> - <LI><A HREF="#mul" NAME="TOCmul">Multi Server is superior, ...</A> - <LI><A HREF="#the" NAME="TOCthe">The Hurd even more so.</A> - <LI><A HREF="#mac" NAME="TOCmac">Mach Inter Process Communication</A> - <LI><A HREF="#how" NAME="TOChow">How to get a port?</A> - <LI><A HREF="#exa" NAME="TOCexa">Example of <SAMP>hurd_file_name_lookup</SAMP></A> - <LI><A HREF="#pat" NAME="TOCpat">Pathname resolution example</A> - <LI><A HREF="#map" NAME="TOCmap">Mapping the POSIX Interface</A> - <LI><A HREF="#filser" NAME="TOCfilser">File System Servers</A> - <LI><A HREF="#act" NAME="TOCact">Active vs Passive</A> - <LI><A HREF="#aut" NAME="TOCaut">Authentication</A> - <LI><A HREF="#ope" NAME="TOCope">Operations on authentication ports</A> - <LI><A HREF="#est" NAME="TOCest">Establishing trusted connections</A> - <LI><A HREF="#pas" NAME="TOCpas">Password Server</A> - <LI><A HREF="#pro" NAME="TOCpro">Process Server</A> - <LI><A HREF="#filsys" NAME="TOCfilsys">Filesystems</A> - <LI><A HREF="#dev" NAME="TOCdev">Developing the Hurd</A> - <LI><A HREF="#sto" NAME="TOCsto">Store Abstraction</A> - <LI><A HREF="#deb" NAME="TOCdeb">Debian GNU/Hurd</A> - <LI><A HREF="#stabin" NAME="TOCstabin">Status of the Debian GNU/Hurd binary archive</A> - <LI><A HREF="#stainf" NAME="TOCstainf">Status of the Debian infrastructure</A> - <LI><A HREF="#staarc" NAME="TOCstaarc">Status of the Debian Source archive</A> - <LI><A HREF="#debide" NAME="TOCdebide">Debian GNU/Hurd: Good idea, bad idea?</A> - <LI><A HREF="#end" NAME="TOCend">End</A> -</UL> -<HR> -<H3>Talk about the Hurd</H3> -<P> -This talk about the Hurd was written by Marcus Brinkmann for -<UL> -<LI>OSDEM, Brussels, 4. Feb 2001, -<LI>Frühjahrsfachgespräche, Cologne, 2. Mar 2001 and -<LI>Libre Software Meeting, Bordeaux, 4. Jul 2001. -</UL> - -<H4><A HREF="#TOCint" NAME="int">Introduction</A></H4> -<P> -When we talk about free software, we usually refer to the free -software licenses. We also need relief from software patents, so our -freedom is not restricted by them. But there is a third type of -freedom we need, and that's user freedom. - -<P> -Expert users don't take a system as it is. They like to change the -configuration, and they want to run the software that works best for -them. That includes window managers as well as your favourite text -editor. But even on a GNU/Linux system consisting only of free -software, you can not easily use the filesystem format, network -protocol or binary format you want without special privileges. In -traditional unix systems, user freedom is severly restricted by the -system administrator. - -<P> -The Hurd removes these restrictions from the user. It provides an -user extensible system framework without giving up POSIX compatibility -and the unix security model. Throughout this talk, we will see that -this brings further advantages beside freedom. - -<H4><A HREF="#TOCove" NAME="ove">Overview</A></H4> -<TABLE BORDER="1" CELLPADDING="5" WIDTH="100%"><TR><TD VALIGN="TOP" ALIGN="LEFT"> - -<P> -The Hurd is a POSIX compatible multi-server -system operating on top of the GNU Mach microkernel. - -<P> -Topics: -<UL> - <LI>GNU Mach</LI> - <LI>The Hurd</LI> - <LI>Development</LI> - <LI>Debian GNU/Hurd</LI> -</UL> -</TD></TR></TABLE> - -<P> -The Hurd is a POSIX compatible multi-server system operating on top of -the GNU Mach Microkernel. - -<P> -I will have to explain what GNU Mach is, so we start with that. Then -I will talk about the Hurd's architecture. After that, I will give a -short overview on the Hurd libraries. Finally, I will tell you how -the Debian project is related to the Hurd. - -<H4><A HREF="#TOChis" NAME="his">Historicals</A></H4> -<TABLE BORDER="1" CELLPADDING="5" WIDTH="100%"> -<TR><TD VALIGN="TOP" ALIGN="LEFT"> -<UL> - <LI>1983: Richard Stallman founds the GNU project.</LI> - <LI>1988: Decision is made to use Mach 3.0 as the kernel.</LI> - <LI>1991: Mach 3.0 is released under compatible license.</LI> - <LI>1991: Thomas Bushnell, BSG, founds the Hurd project.</LI> - <LI>1994: The Hurd boots the first time.</LI> - <LI>1997: Version 0.2 of the Hurd is released.<BR><BR></LI> - <LI>1998: Debian hurd-i386 archive is created.</LI> - <LI>2001: Debian GNU/Hurd snapshot fills three CD images.</LI> -</UL> -</TD></TR></TABLE> - -<P> -When Richard Stallman founded the GNU project in 1983, he wanted to -write an operating system consisting only of free software. Very -soon, a lot of the essential tools were implemented, and released -under the GPL. However, one critical piece was missing: The kernel. -<P> -After considering several alternatives, it was decided not to write a -new kernel from scratch, but to start with the Mach microkernel. This -was in 1988, and it was not before 1991 that Mach was released under a -license allowing the GNU project to distribute it as a part of the -system. -<P> -In 1998, I started the Debian GNU/Hurd project, and in 2001 the number -of available GNU/Hurd packages fills three CD images. - -<H4><A HREF="#TOCker" NAME="ker">Kernel Architectures</A></H4> -<TABLE BORDER="1" CELLPADDING="5" WIDTH="100%"><TR><TD VALIGN="TOP" ALIGN="LEFT"> -<P> -Microkernel: -<UL> - <LI>Enforces resource management (paging, scheduling)</LI> - <LI>Manages tasks</LI> - <LI>Implements message passing for IPC</LI> - <LI>Provides basic hardware support</LI> -</UL> -<P> -Monolithic kernel: -<UL> - <LI>No message passing necessary</LI> - <LI>Rich set of features (filesystems, authentication, network - sockets, POSIX interface, ...)</LI> -</UL> -</TD></TR></TABLE> -<P> -Microkernels were very popular in the scientific world around that -time. They don't implement a full operating system, but only the -infrastructure needed to enable other tasks to implement most -features. In contrast, monolithical kernels like Linux contain -program code of device drivers, network protocols, process management, -authentication, file systems, POSIX compatible interfaces and much -more. -<P> -So what are the basic facilities a microkernel provides? In general, -this is resource management and message passing. Resource management, -because the kernel task needs to run in a special privileged mode of -the processor, to be able to manipulate the memory management unit and -perform context switches (also to manage interrupts). Message -passing, because without a basic communication facility the other -tasks could not interact to provide the system services. Some -rudimentary hardware device support is often necessary to bootstrap -the system. So the basic jobs of a microkernel are enforcing the -paging policy (the actual paging can be done by an external pager -task), scheduling, message passing and probably basic hardware device -support. -<P> -Mach was the obvious choice back then, as it provides a rich set of -interfaces to get the job done. Beside a rather brain-dead device -interface, it provides tasks and threads, a messaging system allowing -synchronous and asynchronous operation and a complex interface for -external pagers. It's certainly not one of the sexiest microkernels -that exist today, but more like a big old mama. The GNU project -maintains its own version of Mach, called GNU Mach, which is based on -Mach 4.0. In addition to the features contained in Mach 4.0, the GNU -version contains many of the Linux 2.0 block device and network card -drivers. -<P> -A complete treatment of the differences between a microkernel and -monolithical kernel design can not be provided here. But a couple of -advantages of a microkernel design are fairly obvious. - -<H4><A HREF="#TOCmic" NAME="mic">Micro vs Monolithic</A></H4> -<TABLE BORDER="1" CELLPADDING="5" WIDTH="100%"><TR><TD VALIGN="TOP" ALIGN="LEFT"> -<P> -Microkernel -<UL> - <LI>Clear cut responsibilities - <LI>Flexibility in operating system design, easier debugging</LI> - <LI>More stability (less code to break)</LI> - <LI>New features are not added to the kernel</LI> -</UL> -<P> -Monolithic kernel -<UL> - <LI>Intolerance or creeping featuritis</LI> - <LI>Danger of spaghetti code</LI> - <LI>Small changes can have far reaching side effects</LI> -</UL> -</TD></TR></TABLE> -<P> -Because the system is split up into several components, clean -interfaces have to be developed, and the responsibilities of each part -of the system must be clear. -<P> -Once a microkernel is written, it can be used as the base for several -different operating systems. Those can even run in parallel which -makes debugging easier. When porting, most of the hardware dependant -code is in the kernel. -<P> -Much of the code that doesn't need to run in the special kernel mode -of the processor is not part of the kernel, so stability increases -because there is simply less code to break. -<P> -New features are not added to the kernel, so there is no need to hold -the barrier high for new operating system features. -<P> -Compare this to a monolithical kernel, where you either suffer from -creeping featuritis or you are intolerant of new features (we see both -in the Linux kernel). -<P> -Because in a monolithical kernel, all parts of the kernel can access -all data structures in other parts, it is more likely that short cuts -are used to avoid the overhead of a clean interface. This leads to a -simple speed up of the kernel, but also makes it less comprehensible -and more error prone. A small change in one part of the kernel can -break remote other parts. - -<H4><A HREF="#TOCsin" NAME="sin">Single Server vs Multi Server</A></H4> -<TABLE BORDER="1" CELLPADDING="5" WIDTH="100%"><TR><TD VALIGN="TOP" ALIGN="LEFT"> -<P> -Single Server -<UL> - <LI>A single task implements the functionality of the operating system.</LI> -</UL> -<P> -Multi Server -<UL> - <LI>Many tasks cooperate to provide the system's functionality.</LI> - <LI>One server provides only a small but well-defined part of the - whole system.</LI> - <LI>The responsibilities are distributed logically among the servers.</LI> -</UL> -<P> -A single-server system is comparable to a monolithic kernel system. It -has similar -advantages and disadvantages. -</TD></TR></TABLE> -<P> -There exist a couple of operating systems based on Mach, but they all -have the same disadvantages as a monolithical kernel, because those -operating systems are implemented in one single process running on top -of the kernel. This process provides all the services a monolithical -kernel would provide. This doesn't make a whole lot of sense (the -only advantage is that you can probably run several of such isolated -single servers on the same machine). Those systems are also called -single-server systems. The Hurd is the only usable multi-server -system on top of Mach. In the Hurd, there are many server programs, -each one responsible for a unique service provided by the operating -system. These servers run as Mach tasks, and communicate using the -Mach message passing facilities. One of them does only provide a -small part of the functionality of the system, but together they build -up a complete and functional POSIX compatible operating system. - -<H4><A HREF="#TOCmul" NAME="mul">Multi Server is superior, ...</A></H4> -<TABLE BORDER="1" CELLPADDING="5" WIDTH="100%"><TR><TD VALIGN="TOP" ALIGN="LEFT"> -<P> -Any multi-server has advantages over single-server: -<UL> - <LI>Clear cut responsibilities</LI> - <LI>More stability: If one server dies, all others remain</LI> - <LI>Easier development cycle: Testing without reboot (or replacing - running servers), debugging with gdb</LI> - <LI>Easier to make changes and add new features -</UL> -</TD></TR></TABLE> -<P> -Using several servers has many advantages, if done right. If a file -system server for a mounted partition crashes, it doesn't take down -the whole system. Instead the partition is "unmounted", and -you can try to start the server again, probably debugging it this time -with gdb. The system is less prone to errors in individual -components, and over-all stability increases. The functionality of -the system can be extended by writing and starting new servers -dynamically. (Developing these new servers is easier for the reasons -just mentioned.) -<P> -But even in a multi-server system the barrier between the system and -the users remains, and special privileges are needed to cross it. We -have not achieved user freedom yet. - -<H4><A HREF="#TOCthe" NAME="the">The Hurd even more so.</A></H4> -<TABLE BORDER="1" CELLPADDING="5" WIDTH="100%"><TR><TD VALIGN="TOP" ALIGN="LEFT"> -<P> -The Hurd goes beyond all this, and allows users to write and run their -servers, too! -<UL> - <LI>Users can replace system servers dynamically with their own - implementations.</LI> - <LI>Users can decide what parts of the remainder of the system they - want to use.</LI> - <LI>Users can extend the functionality of the system.</LI> - <LI>No mutual trust necessary to make use of other users - services.</LI> - <LI>Security of the system is not harmed by trusting users - services.</LI> -</UL> -</TD></TR></TABLE> -<P> -To quote Thomas Bushnell, BSG, from his paper -[[``Towards_a_New_Strategy_of_OS_design''_(1996)|hurd-paper]]: -<BLOCKQUOTE> -The GNU Hurd, by contrast, is designed to make the area of system code -as limited as possible. Programs are required to communicate only -with a few essential parts of the kernel; the rest of the system is -replaceable dynamically. Users can use whatever parts of the -remainder of the system they want, and can easily add components -themselves for other users to take advantage of. No mutual trust need -exist in advance for users to use each other's services, nor does the -system become vulnerable by trusting the services of arbitrary users. -</BLOCKQUOTE> - -<P> -<EM>So the Hurd is a set of servers running on top of the Mach -micro-kernel, providing a POSIX compatible and extensible operating -system. What servers are there? What functionality do they provide, -and how do they cooperate?</EM> - -<H4><A HREF="#TOCmac" NAME="mac">Mach Inter Process Communication</A></H4> -<TABLE BORDER="1" CELLPADDING="5" WIDTH="100%"><TR><TD VALIGN="TOP" ALIGN="LEFT"> -<P> -Ports are message queues which can be used as one-way communication -channels. -<UL> - <LI>Port rights are receive, send or send-once</LI> - <LI>Exactly one receiver</LI> - <LI>Potentially many senders</LI> -</UL> -<P> -MIG provides remote procedure calls on top of Mach IPC. RPCs look like -function calls to the user. -</TD></TR></TABLE> -<P> -Inter-process communication in Mach is based on the ports concept. A -port is a message queue, used as a one-way communication channel. In -addition to a port, you need a port right, which can be a send right, -receive right, or send-once right. Depending on the port right, you -are allowed to send messages to the server, receive messages from it, -or send just one single message. -<P> -For every port, there exists exactly one task holding the receive -right, but there can be no or many senders. The send-once right is -useful for clients expecting a response message. They can give a -send-once right to the reply port along with the message. The kernel -guarantees that at some point, a message will be received on the reply -port (this can be a notification that the server destroyed the -send-once right). -<P> -You don't need to know much about the format a message takes to be -able to use the Mach IPC. The Mach interface generator mig hides the -details of composing and sending a message, as well as receiving the -reply message. To the user, it just looks like a function call, but -in truth the message could be sent over a network to a server running -on a different computer. The set of remote procedure calls a server -provides is the public interface of this server. - - -<H4><A HREF="#TOChow" NAME="how">How to get a port?</A></H4> -<TABLE BORDER="1" CELLPADDING="5" WIDTH="100%"><TR><TD VALIGN="TOP" ALIGN="LEFT"> -<P> -Traditional Mach: -<UL> - <LI>Nameserver provides ports to all registered servers.</LI> - <LI>The nameserver port itself is provided by Mach.</LI> - <LI>Like a phone book: One list.</LI> -</UL> -<P> -The Hurd: -<UL> - <LI>The filesystem is used as the server namespace.</LI> - <LI>Root directory port is inserted into each task.</LI> - <LI>The C library finds other ports with hurd_file_name_lookup, - performing a pathname resolution.</LI> - <LI>Like a tree of phone books.</LI> -</UL> -</TD></TR></TABLE> -<P> -So how does one get a port to a server? You need something like a -phone book for server ports, or otherwise you can only talk to -yourself. In the original Mach system, a special nameserver is -dedicated to that job. A task could get a port to the nameserver from -the Mach kernel and ask it for a port (with send right) to a server -that registered itself with the nameserver at some earlier time. -<P> -In the Hurd, there is no nameserver. Instead, the filesystem is used -as the server namespace. This works because there is always a root -filesystem in the Hurd (remember that the Hurd is a POSIX compatible -system); this is an assumption the people who developed Mach couldn't -make, so they had to choose a different strategy. You can use the -function hurd_file_name_lookup, which is part of the C library, to get -a port to the server belonging to a filename. Then you can start to -send messages to the server in the usual way. - -<H4><A HREF="#TOCexa" NAME="exa">Example of <SAMP>hurd_file_name_lookup</SAMP></A></H4> -<TABLE BORDER="1" CELLPADDING="5" WIDTH="100%"><TR><TD VALIGN="TOP" ALIGN="LEFT"><PRE> -mach_port_t identity; -mach_port_t pwserver; -kern_return_t err; - -pwserver = hurd_file_name_lookup - ("/servers/password"); - -err = password_check_user (pwserver, - 0 /* root */, "supass", - &identity); -</PRE></TD></TR></TABLE> -<P> -As a concrete example, the special filename -<SAMP>/servers/password</SAMP> can be used to request a port to the -Hurd password server, which is responsible to check user provided -passwords. -<P> -(explanation of the example) - -<H4><A HREF="#TOCpat" NAME="pat">Pathname resolution example</A></H4> -<TABLE BORDER="1" CELLPADDING="5" WIDTH="100%"><TR><TD VALIGN="TOP" ALIGN="LEFT"> -<P> -Task: Lookup /mnt/readme.txt where /mnt has a mounted filesystem. -<UL> - <LI>The C library asks the root filesystem server about - <SAMP>/mnt/readme.txt</SAMP>.</LI> - <LI>The root filesystem returns a port to the mnt filesystem server - (matching <SAMP>/mnt</SAMP>) and the retry name - <SAMP>/readme.txt</SAMP>.</LI> - <LI>The C library asks the mnt filesystem server about - <SAMP>/readme.txt</SAMP>.</LI> - <LI>The mnt filesystem server returns a port to itself and records - that this port refers to the regular file - <SAMP>/readme.txt</SAMP>.</LI> -</UL> -</TD></TR></TABLE> -<P> -The C library itself does not have a full list of all available -servers. Instead pathname resolution is used to traverse through a -tree of servers. In fact, filesystems themselves are implemented by -servers (let us ignore the chicken and egg problem here). So all the -C library can do is to ask the root filesystem server about the -filename provided by the user (assuming that the user wants to resolve -an absolute path), using the <SAMP>dir_lookup</SAMP> RPC. If the -filename refers to a regular file or directory on the filesystem, the -root filesystem server just returns a port to itself and records that -this port corresponds to the file or directory in question. But if a -prefix of the full path matches the path of a server the root -filesystem knows about, it returns to the C library a port to this -server and the remaining part of the pathname that couldn't be -resolved. The C library than has to retry and query the other server -about the remaining path component. Eventually, the C library will -either know that the remaining path can't be resolved by the last -server in the list, or get a valid port to the server in question. - -<H4><A HREF="#TOCmap" NAME="map">Mapping the POSIX Interface</A></H4> -<TABLE BORDER="1" CELLPADDING="5" WIDTH="100%"><TR><TD VALIGN="TOP" ALIGN="LEFT"> -<TABLE BORDER="0" CELLPADDING="10"> -<TR> -<TH>Filedescriptor</TH> -<TH>Port to server providing the file</TH> -</TR><TR> -<TD VALIGN="TOP" ALIGN="LEFT"><SAMP>fd = open(name,...)</SAMP></TD> -<TD VALIGN="TOP" -ALIGN="LEFT"><SAMP>dir_lookup(..,name,..,&port)</SAMP><BR> -[pathname resolution]</TD> -</TR><TR> -<TD VALIGN="TOP" ALIGN="LEFT"><SAMP>read(fd, ...)</SAMP></TD> -<TD VALIGN="TOP" ALIGN="LEFT"><SAMP>io_read(port, ...)</SAMP></TD> -</TR><TR> -<TD VALIGN="TOP" ALIGN="LEFT"><SAMP>write(fd, ...)</SAMP></TD> -<TD VALIGN="TOP" ALIGN="LEFT"><SAMP>io_write(port, ...)</SAMP></TD> -</TR><TR> -<TD VALIGN="TOP" ALIGN="LEFT"><SAMP>fstat(fd, ...)</SAMP></TD> -<TD VALIGN="TOP" ALIGN="LEFT"><SAMP>io_stat(port, ...)</SAMP></TD> -</TR><TR> -<TD VALIGN="TOP" ALIGN="LEFT">...</TD><TD></TD> -</TR> -</TABLE> -</TD></TR></TABLE> -<P> -It should by now be obvious that the port returned by the server can -be used to query the files status, content and other information from -the server, if good remote procedure calls to do that are defined and -implemented by it. This is exactly what happens. Whenever a file is -opened using the C libraries <SAMP>open()</SAMP> call, the C library -uses the above pathname resolution to get a port to a server providing -the file. Then it wraps a file descriptor around it. So in the Hurd, -for every open file descriptor there is a port to a server providing -this file. Many other C library calls like <SAMP>read()</SAMP> and -<SAMP>write()</SAMP> just call a corresponding RPC using the port -associated with the file descriptor. - -<H4><A HREF="#TOCfilser" NAME="filser">File System Servers</A></H4> -<TABLE BORDER="1" CELLPADDING="5" WIDTH="100%"><TR><TD VALIGN="TOP" ALIGN="LEFT"> -<UL> - <LI>Provide file and directory services for ports (and more).</LI> - <LI>These ports are returned by a directory lookup.</LI> - <LI>Translate filesystem accesses through their root path (hence the - name translator).</LI> - <LI>The C library maps the POSIX file and directory interface (and - more) to RPCs to the filesystem servers ports, but also does work on - its own.</LI> - <LI>Any user can install file system servers on inodes they own.</LI> -</UL> -</TD></TR></TABLE> -<P> -So we don't have a single phone book listing all servers, but rather a -tree of servers keeping track of each other. That's really like -calling your friend and asking for the phone number of the blond girl -at the party yesterday. He might refer you to a friend who hopefully -knows more about it. Then you have to retry. -<P> -This mechanism has huge advantages over a single nameserver. First, -note that standard unix permissions on directories can be used to -restrict access to a server (this requires that the filesystems -providing those directories behave). You just have to set the -permissions of a parent directory accordingly and provide no other way -to get a server port. -<P> -But there are much deeper implications. Most of all, a pathname never -directly refers to a file, it refers to a port of a server. That -means that providing a regular file with static data is just one of -the many options the server has to service requests on the file port. -A server can also create the data dynamically. For example, a server -associated with <SAMP>/dev/random</SAMP> can provide new random data -on every <SAMP>io_read()</SAMP> on the port to it. A server -associated with <SAMP>/dev/fortune</SAMP> can provide a new fortune -cookie on every <SAMP>open()</SAMP>. -<P> -While a regular filesystem server will just serve the data as stored -in a filesystem on disk, there are servers providing purely virtual -information, or a mixture of both. It is up to the server to behave -and provide consistent and useful data on each remote procedure call. -If it does not, the results may not match the expectations of the user -and confuse him. -<P> -A footnote from the Hurd info manual: -<BLOCKQUOTE> -(1) You are lost in a maze of twisty little filesystems, all -alike.... -</BLOCKQUOTE> -<P> -Because a server installed in the filesystem namespace translates all -filesystem operations that go through its root path, such a server is -also called "active translator". You can install translators using -the settrans command with the <SAMP>-a</SAMP> option. - -<H4><A HREF="#TOCact" NAME="act">Active vs Passive</A></H4> -<TABLE BORDER="1" CELLPADDING="5" WIDTH="100%"><TR><TD VALIGN="TOP" ALIGN="LEFT"> -<P> -Active Translators: -<UL> - <LI>"<SAMP>settrans -a /cdrom /hurd/isofs /dev/hd2</SAMP>"</LI> - <LI>Are running filesystem servers.</LI> - <LI>Are attached to the root node they translate.</LI> - <LI>Run as a normal process.</LI> - <LI>Go away with every reboot, or even time out.</LI> -</UL> -</TD></TR></TABLE> -<P> -Many translator settings remain constant for a long time. It would be -very lame to always repeat the same couple of dozens settrans calls -manually or at boot time. So the Hurd provides a filesystem extension -that allows to store translator settings inside the filesystem and let -the filesystem servers do the work to start those servers on demand. -Such translator settings are called "passive translators". A passive -translator is really just a command line string stored in an inode of -the filesystem. If during a pathname resolution a server encounters -such a passive translator, and no active translator does exist already -(for this node), it will use this string to start up a new translator -for this inode, and then let the C library continue with the path -resolution as described above. Passive translators are installed with -settrans using the <SAMP>-p</SAMP> option (which is already the -default). - -<TABLE BORDER="1" CELLPADDING="5" WIDTH="100%"><TR><TD VALIGN="TOP" ALIGN="LEFT"> -<P> -Passive Translators: -<UL> - <LI>"<SAMP>settrans /mnt /hurd/ext2fs /dev/hd1s1</SAMP>"</LI> - <LI>Are stored as command strings into an inode.</LI> - <LI>Are used to start a new active translator if there isn't - one.</LI> - <LI>Startup is transparent to the user.</LI> - <LI>Startup happens the first time the server is needed.</LI> - <LI>Are permanent across reboots (like file data).</LI> -</UL> -</TD></TR></TABLE> -<P> -So passive translators also serve as a sort of automounting feature, -because no manual interaction is required. The server start up is -deferred until the service is need, and it is transparent to the user. -<P> -When starting up a passive translator, it will run as a normal process -with the same user and group id as those of the underlying inode. Any -user is allowed to install passive and active translators on inodes -that he owns. This way the user can install new servers into the -global namespace (for example, in his home or tmp directory) and thus -extend the functionality of the system (recall that servers can -implement other remote procedure calls beside those used for files and -directories). A careful design of the trusted system servers makes -sure that no permissions leak out. -<P> -In addition, users can provide their own implementations of some of -the system servers instead the system default. For example, they can -use their own exec server to start processes. The user specific exec -server could for example start java programs transparently (without -invoking the interpreter manually). This is done by setting the -environment variable <SAMP>EXECSERVERS</SAMP>. The systems default -exec server will evaluate this environment variable and forward the -RPC to each of the servers listed in turn, until some server accepts -it and takes over. The system default exec server will only do this -if there are no security implications. (XXX There are other ways to -start new programs than by using the system exec server. Those are -still available.) -<P> -Let's take a closer look at some of the Hurd servers. It was already -mentioned that only few system servers are mandatory for users. To -establish your identity within the Hurd system, you have to -communicate with the trusted systems authentication server -<SAMP>auth</SAMP>. To put the system administrator into control over -the system components, the process server does some global -bookkeeping. -<P> -But even these servers can be ignored. However, registration with the -authentication server is the only way to establish your identity -towards other system servers. Likewise, only tasks registered as -processes with the process server can make use of its services. - -<H4><A HREF="#TOCaut" NAME="aut">Authentication</A></H4> -<TABLE BORDER="1" CELLPADDING="5" WIDTH="100%"><TR><TD VALIGN="TOP" ALIGN="LEFT"> -<P> -A user identity is just a port to an authserver. The auth server -stores four set of ids for it: -<UL> - <LI>effective user ids</LI> - <LI>effective group ids</LI> - <LI>available user ids</LI> - <LI>available group ids</LI> -</UL> -<P> -Basic properties: -<UL> - <LI>Any of these can be empty.</LI> - <LI>A 0 among the user ids identifies the superuser.</LI> - <LI>Effective ids are used to check if the user has the - permission.</LI> - <LI>Available ids can be turned into effective ids on user - request.</LI> -</UL> -</TD></TR></TABLE> -<P> -The Hurd auth server is used to establish the identity of a user for a -server. Such an identity (which is just a port to the auth server) -consists of a set of effective user ids, a set of effective group ids, -a set of available user ids and a set of available group ids. Any of -these sets can be empty. - -<H4><A HREF="#TOCope" NAME="ope">Operations on authentication ports</A></H4> -<TABLE BORDER="1" CELLPADDING="5" WIDTH="100%"><TR><TD VALIGN="TOP" ALIGN="LEFT"> -<P> -The auth server provides the following operations on ports: -<UL> - <LI>Merge the ids of two ports into a new one.</LI> - <LI>Return a new port containing a subset of the ids in a port.</LI> - <LI>Create a new port with arbitrary ids (superuser only).</LI> - <LI>Establish a trusted connection between users and servers.</LI> -</UL> -</TD></TR></TABLE> -<P> -If you have two identities, you can merge them and request an identity -consisting of the unions of the sets from the auth server. You can -also create a new identity consisting only of subsets of an identity -you already have. What you can't do is extending your sets, unless -you are the superuser which is denoted by having the user id 0. - -<H4><A HREF="#TOCest" NAME="est">Establishing trusted connections</A></H4> -<TABLE BORDER="1" CELLPADDING="5" WIDTH="100%"><TR><TD VALIGN="TOP" ALIGN="LEFT"> -<UL> - <LI>User provides a rendezvous port to the server (with - <SAMP>io_reauthenticate</SAMP>).</LI> - <LI>User calls <SAMP>auth_user_authenticate</SAMP> on the - authentication port (his identity), passing the rendezvous port.</LI> - <LI>Server calls <SAMP>auth_server_authenticate</SAMP> on its - authentication port (to a trusted auth server), passing the - rendezvous port and the server port.</LI> - <LI>If both authentication servers are the same, it can match the - rendezvous ports and return the server port to the user and the user - ids to the server.</LI> -</UL> -</TD></TR></TABLE> -<P> -Finally, the auth server can establish the identity of a user for a -server. This is done by exchanging a server port and a user identity -if both match the same rendezvous port. The server port will be -returned to the user, while the server is informed about the id sets -of the user. The server can then serve or reject subsequent RPCs by -the user on the server port, based on the identity it received from -the auth server. -<P> -Anyone can write a server conforming to the auth protocol, but of -course all system servers use a trusted system auth server to -establish the identity of a user. If the user is not using the system -auth server, matching the rendezvous port will fail and no server port -will be returned to the user. Because this practically requires all -programs to use the same auth server, the system auth server is -minimal in every respect, and additional functionality is moved -elsewhere, so user freedom is not unnecessarily restricted. - -<H4><A HREF="#TOCpas" NAME="pas">Password Server</A></H4> -<TABLE BORDER="1" CELLPADDING="5" WIDTH="100%"><TR><TD VALIGN="TOP" ALIGN="LEFT"> -<P> -The password server <SAMP>/servers/password</SAMP> runs as root and -returns a new authentication port in exchange for a unix password. -<P> -The ids corresponding to the authentication port match the unix user -and group ids. -<P> -Support for shadow passwords is implemented here. -</TD></TR></TABLE> -<P> -The password server sits at <SAMP>/servers/password</SAMP> and runs as -root. It can hand out ports to the auth server in exchange for a unix -password, matching it against the password or shadow file. Several -utilities make use of this server, so they don't need to be setuid -root. - -<H4><A HREF="#TOCpro" NAME="pro">Process Server</A></H4> -<TABLE BORDER="1" CELLPADDING="5" WIDTH="100%"><TR><TD VALIGN="TOP" ALIGN="LEFT"> -<P> -The superuser must remain control over user tasks, so: -<UL> - <LI>All mach tasks are associated with a PID in the system default - proc server.</LI> -</UL> -<P> -Optionally, user tasks can store: -<UL> - <LI>Their environment variables.</LI> - <LI>Their argument vector.</LI> - <LI>A port, which others can request based on the PID (like a - nameserver).</LI> -</UL> -<P> -Also implemented in the proc server: -<UL> - <LI>Sessions and process groups.</LI> - <LI>Global configuration not in Mach, like hostname, hostid, system - version.</LI> -</UL> -</TD></TR></TABLE> -<P> -The process server is responsible for some global bookkeeping. As -such it has to be trusted and is not replaceable by the user. -However, a user is not required to use any of its service. In that -case the user will not be able to take advantage of the POSIXish -appearance of the Hurd. -<P> -The Mach Tasks are not as heavy as POSIX processes. For example, -there is no concept of process groups or sessions in Mach. The proc -server fills in the gap. It provides a PID for all Mach tasks, and -also stores the argument line, environment variables and other -information about a process (if the mach tasks provide them, which is -usually the case if you start a process with the default -<SAMP>fork()</SAMP>/<SAMP>exec()</SAMP>). A process can also register -a message port with the proc server, which can then be requested by -anyone. So the proc server also functions as a nameserver using the -process id as the name. -<P> -The proc server also stores some other miscellaneous information not -provided by Mach, like the hostname, hostid and system version. -Finally, it provides facilities to group processes and their ports -together, as well as to convert between pids, process server ports and -mach task ports. -<TABLE BORDER="1" CELLPADDING="5" WIDTH="100%"><TR><TD VALIGN="TOP" ALIGN="LEFT"> -<P> -User tasks not registering themselve with proc only have a PID assigned. -<P> -Users can run their own proc server in addition to the system default, -at least for those parts of the interface that don't require superuser -privileges. -</TD></TR></TABLE> -<P> -Although the system default proc server can't be avoided (all Mach -tasks spawned by users will get a pid assigned, so the system -administrator can control them), users can run their own additional -process servers if they want, implementing the features not requiring -superuser privileges. - -<H4><A HREF="#TOCfilsys" NAME="filsys">Filesystems</A></H4> -<TABLE BORDER="1" CELLPADDING="5" WIDTH="100%"><TR><TD VALIGN="TOP" ALIGN="LEFT"> -<P> -Store based filesystems -<UL> - <LI><SAMP>ext2fs</SAMP></LI> - <LI><SAMP>ufs</SAMP></LI> - <LI><SAMP>isofs</SAMP> (iso9660, RockRidge, GNU extensions)</LI> - <LI><SAMP>fatfs</SAMP> (under development)</LI> -</UL> -<P> -Network file systems -<UL> - <LI><SAMP>nfs</SAMP></LI> - <LI><SAMP>ftpfs</SAMP></LI> -</UL> -<P> -Miscellaneous -<UL> - <LI><SAMP>hostmux</SAMP></LI> - <LI><SAMP>usermux</SAMP></LI> - <LI><SAMP>tmpfs</SAMP> (under development)</LI> -</UL> -</TD></TR></TABLE> -<P> -We already talked about translators and the file system service they -provide. Currently, we have translators for the ext2, ufs and iso9660 -filesystems. We also have an nfs client and an ftp filesystem. -Especially the latter is intriguing, as it provides transparent access -to ftp servers in the filesystem. Programs can start to move away -from implementing a plethora of network protocols, as the files are -directly available in the filesystem through the standard POSIX file -interface. - - -<H4><A HREF="#TOCdev" NAME="dev">Developing the Hurd</A></H4> -<TABLE BORDER="1" CELLPADDING="5" WIDTH="100%"><TR><TD VALIGN="TOP" ALIGN="LEFT"> -<P> -Over a dozen libraries support the development of new servers. -<P> -For special server types highly specialized -libraries require only the implementation of a -number of callback functions. -<UL> - <LI>Use <SAMP>libdiskfs</SAMP> for store based filesystems.</LI> - <LI>Use <SAMP>libnetfs</SAMP> for network filesystems, also for - virtual filesystems.</LI> - <LI>Use <SAMP>libtrivfs</SAMP> for simple filesystems providing only - a single file or directory.</LI> -</UL> -</TD></TR></TABLE> -<P> -The Hurd server protocols are complex enough to allow for the -implementation of a POSIX compatible system with GNU extensions. -However, a lot of code can be shared by all or at least similar -servers. For example, all storage based filesystems need to be able to -read and write to a store medium splitted in blocks. The Hurd comes -with several libraries which make it easy to implement new servers. -Also, there are already a lot of examples of different server types in -the Hurd. This makes writing a new server easier. -<P> -<SAMP>libdiskfs</SAMP> is a library that supports writing store based -filesystems like ext2fs or ufs. It is not very useful for filesystems -which are purely virtual, like <SAMP>/proc</SAMP> or files in -<SAMP>/dev</SAMP>. -<P> -<SAMP>libnetfs</SAMP> is intended for filesystems which provide a rich -directory hierarchy, but don't use a backing store (for example ftpfs, -nfs). -<P> -<SAMP>libtrivfs</SAMP> is intended for filesystems which just provide -a single inode or directory. Most servers which are not intended to -provide a filesystem but other services (like -<SAMP>/servers/password</SAMP>) use it to provide a dummy file, so -that file operations on the servers node will not return errors. But -it can also be used to provide meaningful data in a single file, like -a device store or a character device. - -<H4><A HREF="#TOCsto" NAME="sto">Store Abstraction</A></H4> -<TABLE BORDER="1" CELLPADDING="5" WIDTH="100%"><TR><TD VALIGN="TOP" ALIGN="LEFT"> -<P> -Another very useful library is libstore, which is used by all store -based filesystems. It provides a store media abstraction. A store -consists of a store class and a name (which itself can sometimes -contain stores). -<P> -Primitive store classes: -<UL> - <LI>device store like device:hd2, device:hd0s1, device:fd0</LI> - <LI>file store like file:/tmp/disk_image</LI> - <LI>task store like task:PID</LI> - <LI>zero store like zero:4m (like /dev/zero, of size 4 MB)</LI> -</UL> -</TD></TR></TABLE> -<TABLE BORDER="1" CELLPADDING="5" WIDTH="100%"><TR><TD VALIGN="TOP" ALIGN="LEFT"> -<P> -Composed store classes: -<UL> - <LI>copy store like copy:zero:4m</LI> - <LI>gunzip/bunzip2 store like gunzip:device:fd0</LI> - <LI>concat store like concat:device:hd0s2:device:hd1s5</LI> - <LI>ileave store (RAID-0(2))</LI> - <LI>remap store like remap:10+20,50+:file:/tmp/blocks</LI> - <LI>...</LI> -</UL> -<P> -Wanted: A similar abstraction for streams (based on channels), which -can be used by network and character device servers. -</TD></TR></TABLE> -<P> -<SAMP>libstore</SAMP> provides a store abstraction, which is used by -all store based filesystems. The store is determined by a type and a -name, but some store types modify another store rather than providing -a new store, and thus stores can be stacked. For example, the device -store type expects a Mach device, but the remap store expects a list -of blocks to pick from another store, like remap:1+:device:hd2, which -would pick all blocks from hd2 but the first one, which skipped. -Because this functionality is provided in a library, all libstore -using filesystems support many different store kinds, and adding a new -store type is enough to make all store based filesystems support it. - -<H4><A HREF="#TOCdeb" NAME="deb">Debian GNU/Hurd</A></H4> -<TABLE BORDER="1" CELLPADDING="5" WIDTH="100%"><TR><TD VALIGN="TOP" ALIGN="LEFT"> -<P> -Goal: -<UL> - <LI>Provide a binary distribution of the Hurd that is easy to - install.</LI> -</UL> -<P> -Constraints: -<UL> - <LI>Use the same source packages as Debian GNU/Linux.</LI> - <LI>Use the same infrastructure: - <UL> - <LI>Policy</LI> - <LI>Archive</LI> - <LI>Bug tracking system</LI> - <LI>Release process</LI> - </UL></LI> -</UL> -<P> -Side Goal: -<UL> - <LI>Prepare Debian for the future: - <UL> - <LI>More flexibility in the base system</LI> - <LI>Identify dependencies on the Linux kernel</LI> - </UL></LI> -</UL> -</TD></TR></TABLE> -<P> -The Debian distribution of the GNU Hurd that I started in 1998 is -supposed to become a complete binary distribution of the Hurd that is -easy to install. - -<H4><A HREF="#TOCstabin" NAME="stabin">Status of the Debian GNU/Hurd binary archive</A></H4> -<P> -See -<A HREF="http://buildd.debian.org/stats/graph.png">http://buildd.debian.org/stats/graph.png</A> -for the most current version of the statistic. - -<H4><A HREF="#TOCstainf" NAME="stainf">Status of the Debian infrastructure</A></H4> -<TABLE BORDER="1" CELLPADDING="5" WIDTH="100%"><TR><TD VALIGN="TOP" ALIGN="LEFT"> -<P> -Plus: -<UL> - <LI>Source packages can identify build and host OS using - dpkg-architecture.</LI> -</UL> -<P> -Minus: -<UL> - <LI>The binary architecture field is insufficient.</LI> - <LI>The BTS has no architecture tag.</LI> - <LI>The policy/FHS need (small) Hurd specific extensions.</LI> -</UL> -</TD></TR></TABLE> -<P> -While good compatibiity can be achieved at the source level, -the binary packages can not always express their relationship -to the available architectures sufficiently. -<P> -For example, the Linux version of makedev is binary-all, where -a binary-all-linux relationship would be more appropriate. -<P> -More work has to be done here to fix the tools. - -<H4><A HREF="#TOCstaarc" NAME="staarc">Status of the Debian Source archive</A></H4> -<TABLE BORDER="1" CELLPADDING="5" WIDTH="100%"><TR><TD VALIGN="TOP" ALIGN="LEFT"> -<UL> - <LI>Most packages just work.</LI> - <LI>Maintainers are usually responsive and cooperative.</LI> - <LI>Turtle, the autobuilder, crunches through the whole list right - now.</LI> -</UL> -<P> -Common pitfalls are POSIX incompatibilities: -<UL> - <LI>Upstream: - <UL> - <LI>Unconditional use of <SAMP>PATH_MAX</SAMP> - (<SAMP>MAXPATHLEN</SAMP>), <SAMP>MAXHOSTNAMELEN</SAMP>.</LI> - <LI>Unguarded use of Linux kernel features.</LI> - <LI>Use of legacy interfaces (<SAMP>sys_errlist</SAMP>, - <SAMP>termio</SAMP>).</LI> - </UL></LI> - <LI>Debian: - <UL> - <LI>Unguarded activation of extensions available with Linux.</LI> - <LI>Low quality patches.</LI> - <LI>Assuming GNU/Linux in package scripts.</LI> - </UL></LI> -</UL> -</TD></TR></TABLE> -<P> -Most packages are POSIX compatible and can be compiled without -changes on the Hurd. The maintainers of the Debian source packages -are usually very kind, responsiver and helpful. -<P> -The Turtle autobuilder software (<A -HREF="http://turtle.sourceforge.net" >http://turtle.sourceforge.net</A>) -builds the Debian packages on the Hurd automatically. - -<H4><A HREF="#TOCdebide" NAME="debide">Debian GNU/Hurd: Good idea, bad idea?</A></H4> -<TABLE BORDER="1" CELLPADDING="5" WIDTH="100%"><TR><TD VALIGN="TOP" ALIGN="LEFT"> -<P> -Upstream benefits: -<UL> - <LI>Software packages become more portable.</LI> -</UL> -<P> -Debian benefits: -<UL> - <LI>Debian becomes more portable.</LI> - <LI>Maintainers learn about portability and other systems.</LI> - <LI>Debian gets a lot of public recognition.</LI> -</UL> -<P> -GNU/Hurd benefits: -<UL> - <LI>Large software base.</LI> - <LI>Great infrastructure.</LI> - <LI>Nice community to partner with.</LI> -</UL> -</TD></TR></TABLE> -<P> -The sheet lists the advantages of all groups involved. - -<H4><A HREF="#TOCend" NAME="end">End</A></H4> -<TABLE BORDER="1" CELLPADDING="5" WIDTH="100%"><TR><TD VALIGN="TOP" ALIGN="LEFT"> -<P> -Join us at -<UL> - <LI><A HREF="http://hurd.gnu.org/" >http://hurd.gnu.org/</A></LI> - <LI><A HREF="http://www.debian.org/ports/hurd" - >http://www.debian.org/ports/hurd</A></LI> - <LI><A HREF="http://www.hurdfr.org" - >http://www.hurdfr.org</A></LI> -</UL> -</TD></TR></TABLE> -<P> -List of contacts. |