5
Server

mount and export

The kernel maps system calls like open() , read() , write() etc. into function calls on devices.

One of the devices is #M. It can only be accessed by the kernel. #M translates function calls into remote function calls, i.e., Styx transactions, to processes for which #M has file connections (ref FD).

#M gets these file connections through the system call mount() :

include "sys.m";

sys := load Sys Sys->PATH;

if (sys->mount(fd, "/n/client", sys->MAFTER|sys->MCREATE, "") < 0)
sys->print("mount failed: %r\n");

The command mount gets the ref FD as a network connection to the port styx (usually 6666) for some host:

perky$ mount -ac net!$FILESERVER /n/client

$FILESERVER can be replaced by a DNS name or IP address. mount does not permit an explicit port, however.

mount uses the same flags as bind. Additionally, a security algorithm can be specified with -C for the Secure Socket Layer : md5 or sha for digesting, rc4 for encryption, and in the US two versions of DES.

mount() links up with the system call export() at the other end of a connection:

if (sys->export(fd, sys->EXPWAIT) < 0)
sys->print("export failed: %r\n");

export() delivers it's entire namespace to #M and from there to the directory specified for mount(). It is advisable to use newns() to create a reduced namespace first.

clone is a Limbo program which uses the module styx to copy and display Styx messages:

perky$ clone
Usage: clone [-Av] net!machine[!port] port
clone -f [-abv] net!machine[!port] path/file

-A suppresses authentication. -f requests that clone use #s to park a network connection as a file. A new directory is mounted in path using the flags -a or -bwhich contains just file.

mnt extends mount to match clone:

perky$ mnt
Usage: mnt [-abcr] [-Ap | -C alg] net!machine[!port] dir
mnt -f [-abcpr] path/file dir

-A suppresses authentication. -p will request a password. -p mounts a file:

$ emu
perky$ lib/srv
perky$ clone -v net!perky 1234
perky$ clone -fb net!perky!1234 /tmp/srv
perky$ mnt -f /tmp/srv /n/client

lib/srv starts file service, the first clone produces a trace, the second one connects to the file mount with mnt. Altogether this permits watching Styx.

odin

odin evolved from u9fs, a UNIX program that makes a UNIX tree accessible for Plan 9. odin serves a UNIX tree for Styx; however, it usually requires a UNIX password as aname in Tattach and does not support the Secure Socket Layer.

$ odin -p 1234 -v
$ emu
perky$ lib/srv
perky$ mnt -Ap net!perky!1234 /n/client

odin illustrates the internal workings of a server using ANSI-C. With the option -v odin displays the transactions as diagnostic output.

odin should be run by root. In this case, an argument can be specified for chroot(). If another user runs odin, it serves / and cannot act on all aspects of protection.

15/Mar/1998