FILESYS(4spp)       RISC/os Reference Manual        FILESYS(4spp)



NAME
     filesys - general description of file system interface

SYNOPSIS
     {
          initroutine,  openroutine,  readroutine,
          writeroutine, ioctlroutine, closeroutine
     }

DESCRIPTION
     New file systems and protocol support is added to the stan-
     dalone I/O system by writing the file system or protocol
     implementation routines and making a new entry to the file
     system configuration structure fstable in the file
     saio/conf.c.  The format of a file system configuration
     entry is shown above.  The fields in a file system confi-
     guration entry have the following usage:

     init_routine(iop)
          The initialization routine is called during the startup
          initialization of the standalone I/O library when a
          program is run.  The main function of the initializa-
          tion routine is to initialize global data of the file
          system routines.  The initialization routine usually
          does not reference a hardware device.

     open_routine(iop, path, flags)
          The open routine is called in response to a read(3spp)
          request.  It is called after the standalone I/O system
          has called the device driver open routine.  It is
          passed a pointer to a struct iob associated with the
          descriptor being opened, the path component of the file
          to be opened, and flags indicating if the open is
          read-only, write-only, or read-write.  The main func-
          tion of the file system open routine is to establish
          enough context regarding the file named in path so that
          future read and write requests can be accomplished.
          For UNIX file systems, this is accomplished by locating
          and reading the appropriate struct inode from the dev-
          ice.  Protocol implementations locate an appropriate
          file server during the open.

     read_routine(iop, buffer, count)
          The read routine is passed a pointer to a struct iob
          associated with the descriptor being read, the address
          of a user's buffer, and a byte count indicating the
          amount of data to transfer.  The read routine accom-
          plishes the data transfer by referring to data esta-
          blished during the open and making calls to the lower
          level device driver.  The lower level device driver is
          called indirectly through the struct iob, allowing a
          file system implementation to serve multiple devices.



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FILESYS(4spp)       RISC/os Reference Manual        FILESYS(4spp)



     write_routine(iop,  buffer, count)
          The write routine functions similarly to the read rou-
          tine to accomplish writes to a file system or via a
          protocol.

     ioctl_routine(iop, command, argument)
          The ioctl routine implements any special functions pos-
          sible on the file system or protocol.  It is passed a
          struct iob pointer associated with the descriptor being
          operated on, a command indicating the operation to per-
          form, and an argument that is specific to the command.

     close_routine(iop)
          The close routine is passed a pointer to a struct iob
          associated with the descriptor being closed.  The close
          routine performs any clean-up activities necessary with
          terminating access to the descriptor.

SEE ALSO
     intro(4spp)



































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