REGISTRY(4)REGISTRY(4)NAME
registry, regquery - registration of services dynamically
SYNOPSIS
ndb/registry [ -f dbfile ]
ndb/regquery [ -m mntpt ] [ -n ] [ attr value ] ...
DESCRIPTION
Registry is a file server that provides registration and location of
services by their attributes where services come and go. It was origi‐
nally intended to register Grid resources but has much wider use. Reg‐
istry serves 9P on its standard input. That can be mounted in the
local name space (see below for an example), or served over a connec‐
tion (eg, via listen(1)). The conventional local mount point is
/mnt/registry, which is where registries(2) expects to find the local
registry by default. There can, however, be any number of registries
active, each supporting a different group of users and services, in
different authentication domains.
Registry serves a one-level directory containing a few control files
and one file per registered service. All the files are text files with
similar format: zero or more lines of one or more words, separated by
white space (blank or tab). A word can be quoted, using single quotes
in the style of sh(1), allowing it to contain white space or represent
the empty string ''. Within a quoted word, a single quote character is
represented by two adjacent ones. (In programs, use String->quoted
from string(2), or more simply the %q string format of sys-print(2) to
quote strings appropriately.)
The control files are:
new A text file that is opened and written to register a new ser‐
vice. Opening new returns a file descriptor to a new but anony‐
mous service file. It must be written to set its name and ini‐
tial description. The first write contains one or more words:
svcname [ attr value ]..."
The first word, svcname, is the proposed service name. The
write returns an error if the name duplicates any existing name.
Otherwise, a new file svcname will appear in the directory. The
optional attribute value pairs form the initial service descrip‐
tion. The service is removed from the register by default when
the file is closed. To advertise a service without having to
hold open a file descriptor, include an attr named persist with
non-zero value; the service will then remain registered until
explicitly removed (see below).
index A read-only text file containing a list of all the currently-
registered services, one per line. Each line contains a
sequence of words. The first word is the service name and the
remaining ones are paired: attribute name then value.
find A text file which should be opened for reading and writing.
Each write provides a set of attribute/value pairs that acts as
a filter, selecting only those services that possess all the
given attributes with the given values; the value "*" matches
any value. Subsequent reads return a list of services, in the
same format as index, but listing only the selected services.
The selection is made from those available at the time of the
write. There is a separate filter for each open instance of
find, so that several processes can set different filters simul‐
taneously. (Note that after the write, the file offset must be
set to zero using sys-seek(2) before reading.)
event A read-only text file that can be used to detect when changes
are made to the registry. Reading from it blocks until a change
is made. At that point, the read completes and returns a string
with a newline terminated decimal version number representing
the number of changes made to the registry, which matches
Qid.vers for the registry directory. Multiple changes are coa‐
lesced into one report.
A service file created by new may be read by anyone, but may be written
only by its owner. Each write must contain a set of attribute/value
pairs, formatted as above, which adds new attributes to the service
description and changes the value of existing attributes. The file
remains until the service is struck off the register. The owner of a
service can remove its registration at any time by removing the corre‐
sponding service file (eg, using rm(1) or sys-remove(2)).
Typically, most services register themselves dynamically, perhaps using
their locations (eg, network address) as their service names. (Reg‐
istry itself does not interpret the name.) The -f option causes reg‐
istry to load initially a set of static service descriptions from
dbfile, which is in attrdb(6) format. The database entry for each ser‐
vice contains the pair service=svcname, causing registry to make an
entry for the given svcname with attribute/value pairs initialised from
the rest of that database entry. For example:
service=net!click!1234
description='snapshot service' auth=none
Static entries are regarded as persistent but can be removed explicitly
by the registry owner.
Regquery looks for services in the registry mounted at mntpt (default:
/mnt/registry) that match all the given attribute/value pairs. It
prints the resulting list of services, one per line. If the -n option
is given, regquery prints only the service name(s); otherwise it prints
the service description as well. If no attributes are given on the
command line, regquery prompts for successive queries, one per line,
and prints each result.
EXAMPLE
Start a registry that appears at the standard location for local reg‐
istries, /mnt/registry:
mount {ndb/registry} /mnt/registry
Make that registry available to the network on authenticated connec‐
tions:
listen -v 'tcp!*!registry' {export /mnt/registry&}
SOURCE
/appl/cmd/ndb/registry.b
SEE ALSOattrdb(2), registries(2)BUGS
It is not currently possible to have two values with the same attribute
name in the same service description.
REGISTRY(4)
