On Tue, 2005-09-13 at 14:36 -0600, Matthew Wilcox wrote: > > Could you explain the difference please? Why is it preferable to keep > the LUN as an array of bytes instead of a single large integer? > Because set of valid LUN id represented by 8 byte combinations is not isomorphic to the set of unsigned int values from 0 to UINT64_MAX. While scsilun_to_int() will convert legal LUN id into some integer, the int_to_scsilun() function will not produce legal LUN id for any arbitrary integer lun value. For example, sequential LUN scanning should be stopped at int lun = 255 because result of converting value 256 by int_to_scsilun() will be either illegal(best case) or equivalent to int lun = 0. LUN id should be presented to the management layers in a way similar to MAC addresses or FC/SAS/... WWN . E.g. the usual LUN 4 on some FC device will be identified by something like (in 00b, or "Peripheral device addressing"): WWPN = 22:00:00:0c:50:05:df:6d LUN = 00:04:00:00:00:00:00:00 Interestingly enough, the following is also LUN = 4 device, but in a different addressing mode (01b, AKA "Logical unit addressing"): WWPN = 22:00:00:0c:50:05:df:6d LUN = 40:04:00:00:00:00:00:00 Sergey Panov ====================================================================== Any opinions are personal and not necessarily those of my former, present, or future employers. - : send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
