BIND(2)                                                   BIND(2)

          bind, mount, unmount - change name space

          #include <u.h>
          #include <libc.h>

          int bind(char *name, char *old, int flag)

          int mount(int fd, int afd, char *old, int flag, char *aname)

          int unmount(char *name, char *old)

          Bind and mount modify the file name space of the current
          process and other processes in its name space group (see
          fork(2)). For both calls, old is the name of an existing
          file or directory in the current name space where the modi-
          fication is to be made.  The name old is evaluated as
          described in intro(2), except that no translation of the
          final path element is done.

          For bind, name is the name of another (or possibly the same)
          existing file or directory in the current name space.  After
          a successful bind call, the file name old is an alias for
          the object originally named by name; if the modification
          doesn't hide it, name will also still refer to its original
          file.  The evaluation of new happens at the time of the
          bind, not when the binding is later used.

          The fd argument to mount is a file descriptor of an open
          network connection or pipe to a file server, while afd is a
          authentication file descriptor as created by fauth(2) and
          subsequently authenticated.  If authentication is not
          required, afd should be -1.  The old file must be a direc-
          tory.  After a successful mount the file tree served (see
          below) by fd will be visible with its root directory having
          name old.

          The flag controls details of the modification made to the
          name space.  In the following, new refers to the file as
          defined by name or the root directory served by fd. Either
          both old and new files must be directories, or both must not
          be directories.  Flag can be one of:

          MREPL    Replace the old file by the new one.  Henceforth,
                   an evaluation of old will be translated to the new
                   file.  If they are directories (for mount, this
                   condition is true by definition), old becomes a
                   union directory consisting of one directory (the

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     BIND(2)                                                   BIND(2)

                   new file).
          MBEFORE  Both the old and new files must be directories.
                   Add the constituent files of the new directory to
                   the union directory at old so its contents appear
                   first in the union.  After an MBEFORE bind or
                   mount, the new directory will be searched first
                   when evaluating file names in the union directory.
          MAFTER   Like MBEFORE but the new directory goes at the end
                   of the union.

          The flags are defined in <libc.h>.  In addition, there is an
          MCREATE flag that can be OR'd with any of the above.  When a
          create system call (see open(2)) attempts to create in a
          union directory, and the file does not exist, the elements
          of the union are searched in order until one is found with
          MCREATE set.  The file is created in that directory; if that
          attempt fails, the create fails.

          Finally, the MCACHE flag, valid for mount only, turns on
          caching for files made available by the mount.  By default,
          file contents are always retrieved from the server.  With
          caching enabled, the kernel may instead use a local cache to
          satisfy read(5) requests for files accessible through this
          mount point.  The currency of cached data for a file is ver-
          ified at each open(5) of the file from this client machine.

          With mount, the file descriptor fd must be open for reading
          and writing and prepared to respond to 9P messages (see Sec-
          tion 5).  After the mount, the file tree starting at old is
          served by a kernel mnt(3) device.  That device will turn
          operations in the tree into messages on fd. Aname selects
          among different file trees on the server; the null string
          chooses the default tree.

          The file descriptor fd is automatically closed by a success-
          ful mount call.

          The effects of bind and mount can be undone by unmount. If
          name is zero, everything bound to or mounted upon old is
          unbound or unmounted.  If name is not zero, it is evaluated
          as described above for bind, and the effect of binding or
          mounting that particular result on old is undone.


          bind(1), intro(2), fcall(2), auth(2) (particularly amount),
          intro(5), mnt(3), srv(3)

          The return value is a positive integer (a unique sequence

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     BIND(2)                                                   BIND(2)

          number) for success, -1 for failure.  These routines set

          Mount will not return until it has successfully attached to
          the file server, so the process doing a mount cannot be the
          one serving.

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