devreserv(1M)

devreserv -- reserve devices for exclusive use

Synopsis

devreserv [key [devicelist . . .]]

Description

devreserv reserves devices for exclusive use. When the device is no longer required, use devfree to release it.

Command options

key: Designates a unique key on which the device will be reserved. The key must be a positive integer.
devicelist: Defines a list of devices that devreserv will search to find an available device. (The list must be formatted as a single argument to the shell.)

Files

/etc/device.tab
/etc/devlkfile

Usage

devreserv reserves at most one device per devicelist. Each list is searched in linear order until the first available device is found. If a device cannot be reserved from each list, the entire reservation fails.

If you execute devreserv without arguments, devices that are currently reserved are listed, and the keys to which they are reserved. When devreserv is executed with only the key argument, it lists the devices currently reserved to that key.

The commands devreserv and devfree are used to manage the availability of devices on a system. Their use is on a participatory basis and they do not place any constraints on actual access to the device. They provide a centralized bookkeeping point for those who want to use them. To summarize, devices that have been reserved cannot be used by processes that utilize the device reservation functions until the reservation has been canceled. However, processes that do not use device reservation may use a device that has been reserved since such a process would not have checked for its reservation status.

Return values

devreserv exits with one of the following values:

0: The task completed successfully.
1: Command syntax incorrect, invalid option used, or internal error occurred.
2: Device table or device reservation table could not be opened for reading.
3: Device reservation request could not be fulfilled.

Examples

To reserve a floppy disk and a cartridge tape:

   $ key=$$
   $ echo "The Current Process ID is equal to: $key"
   The Current Process ID is equal to: 10658
   $ devreserv $key diskette1,ctape1

To list all devices currently reserved:

   $ devreserv
   disk1         2423
   diskette1     10658
   ctape1        10658

To list all devices currently reserved to a particular key:

   $ devreserv $key
   diskette1
   ctape1

References

devfree(1M)