Writing Device Drivers

attach() Entry Point (SCSI Target Drivers)

After the probe(9E) routine has verified that the expected device is present, attach(9E) is called. attach() performs these tasks:

A SCSI target driver needs to call scsi_probe(9F) again to retrieve the device's inquiry data. The driver must also create a SCSI request sense packet. If the attach is successful, the attach() function should not call scsi_unprobe(9F).

Three routines are used to create the request sense packet: scsi_alloc_consistent_buf(9F), scsi_init_pkt(9F), and scsi_setup_cdb(9F). scsi_alloc_consistent_buf(9F) allocates a buffer that is suitable for consistent DMA. scsi_alloc_consistent_buf() then returns a pointer to a buf(9S) structure. The advantage of a consistent buffer is that no explicit synchronization of the data is required. In other words, the target driver can access the data after the callback. The sd_sense element of the device's scsi_device(9S) structure must be initialized with the address of the sense buffer. scsi_init_pkt(9F) creates and partially initializes a scsi_pkt(9S) structure. scsi_setup_cdb(9F) creates a SCSI command descriptor block, in this case by creating a SCSI request sense command.

Note that a SCSI device is not self-identifying and does not have a reg property. As a result, the driver must set the pm-hardware-state property. Setting pm-hardware-state informs the framework that this device needs to be suspended and then resumed.

The following example shows the SCSI target driver's attach() routine.

Example 17–2 SCSI Target Driver attach(9E) Routine

static int
xxattach(dev_info_t *dip, ddi_attach_cmd_t cmd)
    struct xxstate         *xsp;
    struct scsi_pkt        *rqpkt = NULL;
    struct scsi_device     *sdp;
    struct buf         *bp = NULL;
    int            instance;
    instance = ddi_get_instance(dip);
    switch (cmd) {
        case DDI_ATTACH:
        case DDI_RESUME:
        /* For information, see the "Directory Memory Access (DMA)" */
        /* chapter in this book. */
        return (DDI_FAILURE);
     * Allocate a state structure and initialize it.
    xsp = ddi_get_soft_state(statep, instance);
    sdp = (struct scsi_device *)ddi_get_driver_private(dip);
     * Cross-link the state and scsi_device(9S) structures.
    sdp->sd_private = (caddr_t)xsp;
    xsp->sdp = sdp;
     * Call scsi_probe(9F) again to get and validate inquiry data.
     * Allocate a request sense buffer. The buf(9S) structure
     * is set to NULL to tell the routine to allocate a new one.
     * The callback function is set to NULL_FUNC to tell the
     * routine to return failure immediately if no
     * resources are available.
    bp = scsi_alloc_consistent_buf(&sdp->sd_address, NULL,
    if (bp == NULL)
        goto failed;
     * Create a Request Sense scsi_pkt(9S) structure.
    rqpkt = scsi_init_pkt(&sdp->sd_address, NULL, bp,
    if (rqpkt == NULL)
        goto failed;
     * scsi_alloc_consistent_buf(9F) returned a buf(9S) structure.
     * The actual buffer address is in b_un.b_addr.
    sdp->sd_sense = (struct scsi_extended_sense *)bp->b_un.b_addr;
     * Create a Group0 CDB for the Request Sense command
    if (scsi_setup_cdb((union scsi_cdb *)rqpkt->pkt_cdbp,
        SCMD_REQUEST_SENSE, 0, SENSE__LENGTH, 0) == 0)
         goto failed;;
     * Fill in the rest of the scsi_pkt structure.
     * xxcallback() is the private command completion routine.
    rqpkt->pkt_comp = xxcallback;
    rqpkt->pkt_time = 30; /* 30 second command timeout */
    rqpkt->pkt_flags |= FLAG_SENSING;
    xsp->rqs = rqpkt;
    xsp->rqsbuf = bp;
     * Create minor nodes, report device, and do any other initialization. */
     * Since the device does not have the 'reg' property,
     * cpr will not call its DDI_SUSPEND/DDI_RESUME entries.
     * The following code is to tell cpr that this device
     * needs to be suspended and resumed.
    (void) ddi_prop_update_string(device, dip,
     "pm-hardware-state", "needs-suspend-resume");
    xsp->open = 0;
    return (DDI_SUCCESS);
    if (bp)
    if (rqpkt)
    sdp->sd_private = (caddr_t)NULL;
    sdp->sd_sense = NULL;
    /* Free any other resources, such as the state structure. */
    return (DDI_FAILURE);