The LOADER

The loader is basically a stripped-down kernel. The things that distinguish it from the kernel are:

• uniprocessor only
• virtual addresses = physical addresses
• the only image it can load is the kernel
• no user mode
• special simple command-line interface
• it runs at 'softint' level, so it is non-preemptive, but you can have multiple threads

• It can support just about any load-media device driver written for the kernel in an unaltered form
• It can copy files from distribution media
• It can set system boot parameters
• It can write boot blocks
• It can load the kernel
• It can run as a user-mode program under either OZONE or another operating system (such as Linux) for preparing distribution media

Using the loader

It is booted into memory by the bootblock. It will prompt for commands at the keyboard. If it doesn't get any within 5 seconds, it just goes ahead and boots the kernel using the parameters saved from before. You can manually change any of the parameters by typing in commands before it loads the kernel if you want. There is an HELP command you can type to list out what commands it has. Here is the output of the HELP command (today anyway):

  BARF                             - force access violation
  COPY <from> <to>                 - copy file
  DELETE <file>                    - delete file
  DEVICES [-FULL]                  - list out devices
  DIR <directory>                  - list out directory
  DISMOUNT <fsdevice>              - dismount filesystem device
  DUMP <file> <count> <startvbn>   - dump a file
  EXIT                             - continue boot process
  EXTRA <name> <value>             - set extra name's value
  EXTRAS                           - list out all extras
  HELP                             - print help message
  INIT <disk> <template> <volname> - initialize <disk> using <template> to <volname>
  LOGICALS                         - list out all logical names
  MKDIR <directory>                - create a directory
  MOUNT [-NOCACHE] [-READONLY] <disk> <template> - mount <disk> device on <template> filesystem
  SET <parameter> <value>          - set a parameter to the given value
  SHOW                             - display all the parameters
  TYPE <file>                      - display a file's contents
  WRITEBOOT <loaderimage> [<secpertrk> [<trkpercyl>]] - write bootblock for given loader image

There is also another version of the loader, oz_loader_linux. This will run as an user-mode program under linux. It is the same exact loader program with different drivers. It is used to create a boot disk.

One of the main purposes of the loader is so you can set system parameters before the kernel is loaded into memory. The SET and SHOW commands are provided to access the parameters.

• load_device - specifies the name of the device the kernel is to be booted from (ide_pm.3)
• load_directory - specifies the name of the directory the kernel is located in (/ozone/binaries/)
• load_fstemplate - specifies the name of the filesystem template device (oz_dfs)
• load_script - specifies the name of a file containing loader commands to execute before the kernel is read into memory, relative to load_directory (../startup/smpboot.ldr)
• kernel_image - specifies the name of the kernel image to load (oz_kernel_486.oz)
• startup_image - specifies the name of the image to execute on startup (oz_cli.oz)
• startup_input - specifies the input file for the startup_image (../startup/hardiskstartup.cli)
• startup_output - specifies the output file for the startup_image (console:)
• startup_error - specifies the error file for the startup_image (console:)
• startup_params - specifies the command line parameters for the startup_image
• kernel_stack_size - specifies the size of kernel stacks, in bytes (12288)
• def_user_stack_size - specifies the size of user stacks, in bytes (1048576)
• nonpaged_pool_size - specifies the size of non-paged pool, in bytes (8388608)
• cpu_disable - bitmask of alternate cpu's to disable (0)
• debug_init - set to 1 to have debugger called on initialization (0)
• knl_exception
  • 0 : call kernel debugger on kernel exception
  • 1 : write to active crash dump file on kernel exception
  • 2 : reboot on kernel exception
• tz_offset_rtc - specifies the offset (in minutes) for the RTC (eg, -18000 if RTC is in EST)
• tz_offset_conv - specifies the offset (in minutes) for output conversions (eg, -18000 to display in EST)
• uniprocessor - set to 1 to inhibit starting alternate cpu's on boot (default is 0)
• memory_megabytes - force this physical memory size (0 to have it autosize)
• monochrome - force video output to be black-and-white
• signature - gets set by 'writeboot' command to uniquely identify this boot volume

1. are online
2. have media in them
3. have enough blocks on them to contain the same blocks that the loader image was read in from
4. contain the exact same initial parameter block, including signature, as the currently booted loader