| Field Name | Contents |
|---|---|
| dsc_flags | DSRQ flags honored by this driver (see Table 5-2) |
| dsc_preset | DSRQ preset values (defaults) that are merged with the input ds_flags using logical OR in any request. |
| dsc_bus | Number of this SCSI bus, as encoded in the device minor number. |
| dsc_imax | Maximum target ID for this bus (7 for SCSI, 15 for wide SCSI). |
| dsc_lmax | Maximum number LUN values per ID on this bus. |
| dsc_iomax | Maximum length of a single I/O transfer. |
| dsc_biomax | Maximum length of a buffered I/O transfer. |
The code in Example 5-1 shows a function that tests if a particular flag is supported by a particular bus. The input arguments are a file descriptor for an open device special file, and a flag value (or values) from sys/dsreq.h.
Example 5-1 : Testing the Generic SCSI Configuration
uint
test_dsreq_flags(int dev_fd, uint flag)
{
dsconf_t config;
int ret;
ret = ioctl(dev_fd, DS_CONF, &config);
if (!ret) { /* no problem in ioctl */
return (flag & config.dsc_flags);
} else { /* ioctl failure */
return 0; /* not supported, it seems */
}
}
A program could use the function in Example 5-1 to find out if a particular feature is supported. For example, a test of support for the DSRQ_SYNXFER feature could be coded as follows:
if (test_dsreq_flags(the_dev, DSRQ_SYNXFER)) { /* synchronous negotiation is supported */...