The sgen driver exports the uscsi(7I) interfaces to user processes. The sgen driver can be configured to bind to SCSI devices for which no system driver is available. Examples of such devices include SCSI scanners and SCSI processor devices.

Typically, drivers which export the uscsi(7I) interface unconditionally require that the user present superuser credentials. The sgen driver does not, and relies on the filesystem permissions on its device special file to govern who may access that device. By default, access is restricted and device nodes created by the sgen driver are readable and writable by the superuser exclusively.

It is important to understand that SCSI devices coexisting on the same SCSI bus may potentially interact with each other. This may result from firmware bugs in SCSI devices, or may be made to happen programmatically by sending appropriate SCSI commands to a device. Potentially, any application controlling a device via the sgen driver can introduce data integrity or security problems in that device or any other device sharing the same SCSI bus.

Granting unprivileged users access to an sgen-controlled SCSI device may create other problems. It may be possible for a user to instruct a target device to gather data from another target device on the same bus. It may also be possible for malicious users to install new firmware onto a device to which they are granted access. In environments where security is a concern but user access to devices controlled by the sgen driver is nontheless desired, it is recommended that the devices be separated onto a dedicated SCSI bus to mitigate the risk of data corruption and security violations.

The sgen driver is configurable via the sgen.conf file. In addition to standard SCSI device configuration directives (see scsi(4)), administrators can set several additional properties for the sgen driver.

By default, the sgen driver will not claim or bind to any devices on the system. To do so, it must be configured by the administrator using the inquiry-config-list and/or the device-type-config-list properties.

As with other SCSI drivers, the sgen.conf configuration file enumerates the targets sgen should use. See scsi(4) for more details. For each target enumerated in the sgen.conf file, the sgen driver sends a SCSI INQUIRY command to gather information about the device present at that target. The inquiry-config-list property specifies that the sgen driver should bind to a particular device returning a particular set of inquiry data. The device-type-config-list specifies that the sgen driver should bind to every device that is of a particular SCSI device type. When examining the device, the sgen driver tests to see if it matches an entry in the device-type-config-list or the inquiry-config-list. For more detail on these two properties, see the PROPERTIES section.

When a match against the INQUIRY data presented by a device is made, the sgen driver attaches to that device and creates a device node and link in the /devices and /dev hierarchies. See the FILES section for more information about how these files are named.

It is important for the administrator to ensure that devices claimed by the sgen driver do not conflict with existing target drivers on the system. For example, if the sgen driver is configured to bind to a direct access device, the standard sd.conf file will usually cause sd to claim the device as well. This can cause unpredictable results. In general, the uscsi(7I) interface exported by sd(7d) or st(7d) should be used to gain access to direct access and sequential devices.

The sgen driver is disabled by default. The sgen.conf file is shipped with all of the 'name="sgen" class="scsi" target=...' entries commented out to shorten boot time and to prevent the driver from consuming kernel resources. To use the sgen driver effectively on desktop systems, simply uncomment all of the name="sgen" lines in sgen.conf file. On larger systems with many SCSI controllers, carefully edit the sgen.conf file so that sgen binds only where needed. Refer to driver.conf(4) for further details.

inquiry-config-list

The inquiry-config-list property is a list of pairs of strings that enumerates a list of specific devices to which the sgen driver will bind. Each pair of strings is referred to as <vendorid, productid> in the discussion below.

vendorid

is used to match the Vendor ID reported by the device. The SCSI specification limits Vendor IDs to eight characters. Correspondingly, the length of this string should not exceed eight characters. As a special case, "*" may be used as a wildcard which matches any Vendor ID. This is useful in situations where more than one vendor produces a particular model of a product. vendorid is matched against the Vendor ID reported by the device in a case-insensitive manner.

productid

is used to match the product ID reported by the device. The SCSI specification limits product IDs to sixteen characters (unused characters are filled with the whitespace characters). Correspondingly, the length of productid should not exceed sixteen characters. When examining the product ID of the device, sgen examines the length l of productid and performs a match against only the first l characters in the device's product ID. productid is matched against the product ID reported by the device in a case-insensitive manner.

For example, to match some fictitious devices from ACME corp, the inquiry-config-list can be configured as follows:

To match "UltraToast 4000" devices, regardless of vendor, inquiry-config-list is modified as follows:

To match every device from ACME in the "UltraToast" series (i.e UltraToast 3000, 4000, 5000, ...), inquiry-config-list is modified as follows:

Whitespace characters are significant when specifying productid. For example, a productid of "UltraToast 1000" is fifteen characters in length. If a device reported its ID as "UltraToast 10000", the sgen driver would bind to it because only the first fifteen characters are considered significant when matching. To remedy this situation, specify productid as "UltraToast 1000 ", (note trailing space). This forces the sgen driver to consider all sixteen characters in the product ID to be significant.

device-type-config-list

The device-type-config-list property is a list of strings that enumerate a list of device types to which the sgen driver will bind. The valid device types correspond to those defined by the SCSI-3 SPC Draft Standard, Rev. 11a. These types are:

Alternately, you can specify device types by INQUIRY type ID. To do this, specify type_0x<typenum> in the sgen-config-list. Case is not significant when specifying device type names.

sgen-diag

The sgen-diag property sets the diagnostic output level. This property can be set globally and/or per target/lun pair. sgen-diag is an integer property, and can be set to 0, 1, 2 or 3. Illegal values will silently default to 0. The meaning of each diagnostic level is as follows:

0

No error reporting [default]

1

Report driver configuration information, unusual conditions, and indicate when sense data has been returned from the device.

2

Trace the entry into and exit from routines inside the driver, and provide extended diagnostic data. No error reporting [default].

3

Provide detailed output about command characteristics, driver state, and the contents of each CDB passed to the driver.

In ascending order, each level includes the diagnostics that the previous level reports. See the IOCTLS section for more infomation on the SGEN_IOC_DIAG ioctl.

sgen.conf

Driver configuration file. See CONFIGURATION for more details.

/dev/scsi/<devtype>/cntndn

The sgen driver categorizes each device in a separate directory by its SCSI device type. The files inside the directory are named according to their controller number, target ID and LUN as follows:

cn is the controller number, tn is the SCSI target id and dn is the SCSI LUN

This is analogous to the {controller;target;device} naming scheme, and the controller numbers correspond to the same controller numbers which are used for naming disks. For example, /dev/dsk/c0t0d0s0 and /dev/scsi/scanner/c0t5d0 are both connected to controller c0.

The sgen driver exports the uscsi(7I) interface for each device it manages. This allows a user process to talk directly to a SCSI device for which there is no other driver installed in the system. Additionally, the sgen driver supports the following ioctls:

SGEN_IOC_READY

Send a TEST UNIT READY command to the device and return 0 upon success, non-zero upon failure. This ioctl accepts no arguments.

SGEN_IOC_DIAG

Change the level of diagnostic reporting provided by the driver. This ioctl accepts a single integer argument between 0 and 3. The levels have the same meaning as in the sgen-diag property discussed in PROPERTIES above.

EBUSY

The device was opened by another thread or process. The driver maintains a strict exclusive-open policy for each device.

ENXIO

During opening, the device did not respond to a TEST UNIT READY SCSI command.

ENOTTY

Indicates that the device does not support the requested ioctl function.

Here is an example of how sgen can be configured to bind to scanner devices on the system:

device-type-config-list = "scanner";

The administrator should subsequently uncomment the appropriate name="sgen"... lines for the SCSI target ID to which the scanner corresponds. In this example, the scanner is at target 4.

name= "sgen" class= "scsi" target=4 lun=0;

If it is expected that the scanner will be moved from target to target over time, or that more scanners might be added in the future, it is recommended that all of the name="sgen"... lines be uncommented, so that sgen checks all of the targets on the bus.

For large systems where boot times are a concern, it is recommended that the parent="" property be used to specify which SCSI bus sgen should examine.

driver.conf(4), scsi(4), sd(7D), st(7D), uscsi(7I)

Writing Device Drivers

ANSI Small Computer System Interface-2 (SCSI-2)

SCSI-3 SPC Draft Standard, Rev. 11a