Creating Minor Device Nodes

An important part of the attach process is the creation of minor nodes for the device instance. A minor node contains the information exported by the device and the DDI framework which the system uses to create a special file for the minor node under /devices.

Minor nodes are created when the driver calls ddi_create_minor_node(9F). The driver supplies a minor number, a minor name, a minor node type, and weather the minor node represents a block or character device.

Drivers can choose to create as many or as few minor nodes for a device as it wants to. Solaris expects certain classes of devices to have minor nodes created in a particular format. For example, disk drivers are expected to create 16 minor nodes for each physical disk instance attached; 8 minor nodes are created, representing the a - h block device interfaces, with an additional 8 minor nodes for the a,raw - h,raw character device interfaces.

The minor number passed to ddi_create_minor_node(9F) is defined wholly by the driver itself; the minor number is usually an encoding of the devices instance number with a minor node identifier. Taking the above example, the driver creates minor numbers for each of the minor nodes by taking the devices instance number, shifting it left 3 bits, and OR'ing in the minor node index whose values range from 0 to 15.

The minor node type passed to ddi_create_minor_node(9F) classifies the type of device, such as disks, tapes, network interfaces, frame buffers, and so forth.

The node types DDI_NT_BLOCK, DDI_NT_BLOCK_CHAN, DDI_NT_CD, and DDI_NT_CD_CHAN cause devfsadm(1M) to identify the device instance as a disk and to create a symbolic link in the /dev/dsk or /dev/rdsk directory pointing to the device node in the /devices directory tree.

The node type DDI_NT_TAPE causes devfsadm(1M) to identify the device instance as a tape and to create a symbolic link from the /dev/rmt directory to the device node in the /devices directory tree.

The node types DDI_NT_SERIAL and DDI_NT_SERIAL_DO causes ports(1M) to identify the device instance as a serial port and to create symbolic links from the /dev/term and /dev/cua directories to the device node in the /devices directory tree and to entries to the port monitor database/etc/inittab.

Vendor-supplied strings should include an identifying value to make them unique, such as their name or stock symbol (if appropriate). The string can be used in conjunction with devfsadm(1M) and devlink.tab(4) to create logical names in /dev.