Principles of Operating Systems:Design & Applications

Chapter 3

Inferno Structure and Initialization

Objectives understand where Inferno fits into the history of

operating system development have an appreciation for its position as a

descendant of CTSS, Multics, UNIX, and Plan 9 understand key concepts that are probably

unfamiliar: per-process name spaces, everything as a file server, and Styx

Objectives (cont.) have a mental picture of how the major

components of Inferno are organized and how the source code is organized

understand the division of labor between host-dependent and host-independent initialization

understand how and why the first kproc and the first user process are created “by hand”

Objectives (cont.) understand how the system goes from its

starting point to time-sharing understand that the initial user process

becomes the ancestor of all other processes that run during the lifetime of the system

understand how the system call mechanism of Inferno differs from that of most other systems

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Inferno History Multics begat UNIX–Ken Thompson and Dennis

Ritchie: 1969 UNIX begat Plan 9–Ken Thompson and Rob

Pike Plan 9 begat Inferno Vita Nuova purchased Inferno Vita Nuova open sourced Inferno

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Inferno Concepts Native and Hosted operation

Hosted on FreeBSD, HP-UX, Irix, Linux, Mac OS X, Windows NT, Plan 9, Solaris, and Unixware

Native on CerfCube 1110, CerfCube 250, CerfCube 405, MPC8xx FADS development board, Ipaq , Brightstar ipEngine, JavaStation 1, Arm 7 evaluator kit, IBM PC compatibles, Embedded Planet RPXLite MPC823

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Inferno Concepts (cont.) Per-process name spaces

Can assemble name space from separate files and directories

Name spaces can be inherited Everything is a file server

Extends the UNIX idea that (almost) everything is a file

Directories and files provided by file servers File servers both built in to the kernel and run as

normal applications

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Inferno Concepts (cont.) Styx

Used by all File servers Limbo and Dis

All apps written in Limbo Limbo compiled to Dis Dis runs the same on all host OSs and hardware Just-in-time compilers for most platforms

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Inferno Structure

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Source Directory Structure

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Inferno Initialization Process command line arguments and

environment parameters Identify the host owner Do host OS-specific initialization Create first kernel process Initialize devices Build initial name space

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Inferno Initialization (cont.) Create second kproc to run Dis VM Create initial floating-point state Initialize the Dis VM Load the initial Dis module and set it to ready Start the Dis VM

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In emu/port/main.c: main()

Process Parameters: if((p = getenv("INFERNO")) != nil || (p = getenv("ROOT")) != nil) strecpy(rootdir, rootdir+sizeof(rootdir), p); opt = getenv("EMU"); if(opt != nil && *opt != '\0') { enva[0] = "emu"; envc = tokenize(opt, &enva[1], sizeof(enva)-1) + 1; enva[envc] = 0; option(envc, enva, envusage); } option(argc, argv, usage);

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In emu/port/main.c: main()Set Initial Host Owner eve = strdup("inferno");

Call Host OS-Specific Initialization libinit(imod);

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In emu/Linux/os.c: libinit()Create First kproc p = newproc(); p->kstack = stackalloc(p, &tos); pw = getpwuid(getuid()); if(pw != nil) kstrdup(&eve, pw->pw_name); else print("cannot getpwuid\n"); p->env->uid = getuid(); p->env->gid = getgid(); executeonnewstack(tos, emuinit, imod);

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In emu/port/main.c: emuinit()Initialize Devices chandevinit();

Create Name Space Root e->pgrp->slash = namec("#/", Atodir, 0, 0); cnameclose(e->pgrp->slash->name); e->pgrp->slash->name = newcname("/"); e->pgrp->dot = cclone(e->pgrp->slash);

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In emu/port/main.c: emuinit()Open Standard Input, Output, and Error if(kopen("#c/cons", OREAD) != 0) fprint(2, "failed to make fd0 from #c/cons: %r\n"); kopen("#c/cons", OWRITE); kopen("#c/cons", OWRITE);

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In emu/port/main.c: emuinit()Create Initial Name Space kbind("#U", "/", MAFTER|MCREATE); setid(eve, 0); kbind("#^", "/dev", MBEFORE); /* snarf */ kbind("#^", "/chan", MBEFORE); kbind("#m", "/dev", MBEFORE); /* pointer */ kbind("#c", "/dev", MBEFORE); kbind("#p", "/prog", MREPL); kbind("#d", "/fd", MREPL); kbind("#I", "/net", MAFTER); /* will fail on Plan 9 */

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In emu/port/main.c: emuinit()Create First Dis Interpreter kproc("main", disinit, imod, KPDUPFDG|KPDUPPG|KPDUPENVG);

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In emu/port/dis.c: disinit()Create Initial Floating Point State Fpinit(); Fpsave(&up->env->fpu);

Initialize Dis VM opinit(); modinit(); excinit();

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In emu/port/dis.c: disinit()Load Initial Module root = load(initmod);

Schedule Initial Module p = schedmod(root);

Start the Virtual Machine vmachine(nil);

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System Calls Apps see ordinary cross-module function calls System calls in module, Sys Sys module built in to kernel Calls kernel functionality with normal function

calls

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Summary Inferno derives from a long line of research

operating systems Inferno has a number of unique features Initialization covers everything from beginning

to time-sharing System calls implemented through special

module

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