3
File sytems and namespaces

Resources as file systems

Inferno follows Plan 9 in decribing resources as file systems, i.e., that operations like open, read, and write are used to deal with resources such as devices, processes, etc. In particular, a resource can be represented as a dynamic hierarchy of files.

Example: system console device

	perky$ cat < /dev/cons	read from the keyboard
	hi
	hi
	control-D
	perky$ echo hello > /dev/cons	write to the screen
	hello
	perky$ sh raw >/dev/consctl & cat	raw: no echo, no escapes
	abcdefg	input characters not visible
	done	for 10 seconds
	xyz
	xyz

A shell script is used for the demonstration [no initial comment, no arguments]:
{03/raw}

	echo rawon	write turns raw on
	sleep 10
	echo done >/dev/cons

# to demonstrate 'rawon' for 10 seconds

#

sh raw >/dev/consctl & cat

close turns raw off {}

Example: host command device

	perky$ cat '#C/cmd/clone'	get unused (new) directory
	0

perky$ sh date >'#C/cmd/0/ctl' <'#C/cmd/0/data'
devcmd: 'date
' pid 235
Wed May  7 13:03:50 MET DST 1997
cat: read error: write to hungup channel

A shell script is used so that both files are open before the command is sent to the host and the answer read back:
{03/date}
echo exec date
cat >/dev/cons
{}

Like Plan 9, Inferno uses a process specific namespace which can be inherited and shared or splitt off or erased with pctl() .

The shell splits off its own namespace initially, but shares it with spawned commands. Therefore, cd is a command not built into the shell which, however, cannot affect the original shell when it is used in a shell script.

	perky$ cd /tmp; pwd	expected effect
	/tmp
	perky$ echo 'cd /; pwd' > root
	perky$ sh root; pwd
	/	cd applies to script's shell
	/tmp	...but not to toplevel shell

Similarly, the commands bind, mount and unmount affect the namespace of the calling shell.

Union directories

bind rearranges a namespace. Directories or files can be covered (hidden), directories can be joined.

bind source target

source covers target; a reference to target subsequently finds source. Roughly similar to a symbolic link.

bind -a source target

source and target form a union directory; a reference to target subsequently finds both directories, where the content of source appears after that of target.

bind -b source target

source and target form a union directory; a reference to target subsequently finds both directories, where the content of source appears before that of target.

-c	additionally permits creation of files in the union directory. A new file name is entered
	into the first directory within a union where creation is possible.

Because a private directory can be joined to /dis, the shell needs no PATH. Commands are searched in the current directory, and also in /dis unless the command name has ./ at the beginning.

The Inferno kernel recognizes names starting in # followed by one more character. The character selects a device, i.e., a server that is part of the kernel. Devices offer their resources as file systems, i.e., # can be viewed as the root of the kernel's own file system tree that encompasses the devices. The following results were obtained on Linux:

	perky$ ls -q '#/'	root, inplicitly bound to /
	80000004.00000000 #/chan
	80000001.00000000 #/dev
	80000003.00000000 #/net
	80000005.00000000 #/nvfs
	80000002.00000000 #/prog
	perky$ ls -q '#A'	audio, sound input and output
	00000001.00000000 #A/audio	bound to /dev
	00000002.00000000 #A/audioctl
	perky$ ls -q '#C/cmd'	host commands
	80000004.00000000 #C/cmd/0	bound to /
	00000003.00000000 #C/cmd/clone
	perky$ ls -q '#D'	SSL, filter for sockets
	00000002.00000000 #D/clone	bound to /0/ssl etc.
	perky$ ls -q '#I' '#I/tcp' '#I/udp'	IP, internet connections
	80010002.00000000 #I/tcp	bound to /net
	80000002.00000000 #I/udp
	00010003.00000000 #I/tcp/clone
	00000003.00000000 #I/udp/clone
	perky$ ls -dq '#U'	host file system
	81000002.336c9483 #U	bound to /
	perky$ ls -q '#c'	console etc., bound to /dev
	00000001.00000000 #c/cons	console, input and output
	00000002.00000000 #c/consctl	console, state
	00000003.00000000 #c/keyboard	keyboard, uninterpreted
	00000004.00000000 #c/memory	memory allocation state
	00000005.00000000 #c/null	the void
	00000006.00000000 #c/pin	PIN, can be written once
	00000007.00000000 #c/pointer	mouse, position and buttons
	00000008.00000000 #c/random	random characters
	00000009.00000000 #c/sysname	host name (shell prompt)
	0000000b.00000000 #c/time	microseconds since the epoch
	0000000a.00000000 #c/user	user's name

	perky$ # ls '#d'	draw device bound to /dev
	perky$ ls -q '#p' '#p/3'	processes, bound to /prog
	80000010.00000001 #p/1	directory per process id
	80000030.00000003 #p/3
	00000030.00000003 #p/3/ctl	kill, killgrp terminate process
	00000031.00000003 #p/3/dbgctl	for debugger, controls Dis
	0000003a.00000003 #p/3/fd	shows file connections
	00000032.00000003 #p/3/heap	for debugger, look at things
	00000033.00000003 #p/3/ns	list of all bind/mount operations
	00000034.00000003 #p/3/nsgrp	PID of namespace group
	00000035.00000003 #p/3/pgrp	PID or process group
	00000036.00000003 #p/3/stack	for debugger, shows active modules
	00000037.00000003 #p/3/status	for ps, process state
	00000038.00000003 #p/3/text	[not implemented]
	00000039.00000003 #p/3/wait	blocks until descendant is terminated
	perky$ # ls '#s'	file2chan() , not bound?

/appl/	sources
cmd/	commands in /dis
lib/	modules in /dis/lib
math/	commands in /dis/math
wm/	commands in /dis/wm
work/	some unfinished commands?
/chan/	pipes as channels
/demo/dsp/	distributed sports demonstration
/dev/	devices
/dis/	commands and modules
lib/	server, modules
math/	mathematics: fourier analysis, graphics
mux/	set-top-box demonstration
svc/	server, web? httpd webget
wm/	window system demonstration
/fonts/	bitmaps for fonts
/httpcache/
/icons/
/include/	C includes
/keydb/	CA files
/lib/	data for some programs
/licensedb/	licenses
/locale/	time zones and?
/man/	manual in HTML
/module/	Limbo module imports
/movies/	data for mux
/n/	mount points for network connections
/net/	network connections
/nvfs/
/prog/	process data
/services/	data for some programs
cs/	connection server
db	database
namespace	namespace for server
namespace.init	namespace for wm
/tmp/	temporary files
/usr/	users
inferno/	typical user
keyring/	authentification certificates, privately owned
namespace	namespace
wmsetup	menu for window system

/Hp/	HP-UX system
/Irix/	Irix (MIPS) system
/Linux/	Linux system
386/	architecture
bin/	external commands: emu limbo mk
include/	C includes
lib/
/Nt/	Windows/NT and Windows 95 system
/Solaris/
386/	Solaris/386 system
sparc/	Solaris/Sparc system

15/Mar/1998