REGISTRY(4)                                           REGISTRY(4)

          registry, regquery - registration of services dynamically

          ndb/registry [ -f dbfile ]

          ndb/regquery [ -m mntpt ] [ -n ] [ attr value ] ...

          Registry is a file server that provides registration and
          location of services by their attributes where services come
          and go.  It was originally intended to register Grid
          resources but has much wider use.  Registry serves 9P on its
          standard input.  That can be mounted in the local name space
          (see below for an example), or served over a connection (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

          Registry serves a one-level directory containing a few con-
          trol 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 repre-
          sent 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 appro-

          The control files are:

          new    A text file that is opened and written to register a
                 new service.  Opening new returns a file descriptor
                 to a new but anonymous service file.  It must be
                 written to set its name and initial 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 dupli-
                 cates any existing name.  Otherwise, a new file
                 svcname will appear in the directory.  The optional
                 attribute value pairs form the initial service

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     REGISTRY(4)                                           REGISTRY(4)

                 description.  The service is removed from the regis-
                 ter by default when the file is closed.  To advertise
                 a service without having to hold open a file descrip-
                 tor, 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, select-
                 ing 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
                 simultaneously.  (Note that after the write, the file
                 offset must be set to zero using sys-seek(2) before

          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 coalesced 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.  (Registry itself does not interpret the
          name.)  The -f option causes registry to load initially a
          set of static service descriptions from dbfile, which is in
          attrdb(6) format.  The database entry for each service

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     REGISTRY(4)                                           REGISTRY(4)

          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 exam-

                    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 ser-
          vices, 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.

          Start a registry that appears at the standard location for
          local registries, /mnt/registry:

               mount {ndb/registry} /mnt/registry

          Make that registry available to the network on authenticated

               listen -v 'tcp!*!registry' {export /mnt/registry&}


          attrdb(2), registries(2)

          It is not currently possible to have two values with the
          same attribute name in the same service description.

     Page 3                       Plan 9             (printed 4/19/21)