http://bugzilla.kernel.org/show_bug.cgi?id=12207 --- Comment #31 from Kai Mäkisara <kai.makisara@xxxxxxxxxxx> 2009-04-11 06:11:59 --- On Sat, 11 Apr 2009, bugzilla-daemon@xxxxxxxxxxxxxxxxxxx wrote: > http://bugzilla.kernel.org/show_bug.cgi?id=12207 > > > > > > --- Comment #30 from Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> 2009-04-11 02:38:27 --- > On Fri, 10 Apr 2009 bugzilla-daemon@xxxxxxxxxxxxxxxxxxx wrote: > > > Maybe you should check your facts before telling others where to look. > > max_sectors_kb etc. exist only for block devices (in the Unix sense). > > Tapes are character devices. > > There's no need to be rude. Besides, how would you suggest I check my > facts (bearing in mind that I don't have access to any SCSI or USB tape > drives)? > I am sorry. My words were inappropriate. But even without a tape drive it is possible to read the code. > As the author of st.c, you certainly are the authority on how this > works. And it's definitely true that tapes are char devices. > > But isn't it also true that SCSI tapes, like all SCSI devices, have > their device queue set up by scsi_alloc_queue(), which calls > blk_init_queue(), which registers the queue's kobject using > blk_queue_ktype, whose default attributes include both > queue_max_sectors_entry.attr and queue_max_hw_sectors_entry.attr? And > doesn't this mean that SCSI tapes _do_ have max_sectors_kb etc. > attributes? > Yes, SCSI uses the (Linux) block layer and the attributes do exist within the kernel. They just are not visible in sysfs for character devices. Last night I read the code to find out why. Your analysis is correct but it only shows that the kobject exists. The kobject is added to sysfs using kobject_add() in blk_register_queue() called by add_disk(), which is only called by disk drivers. Whether character devices should add the kobject somewhere in sysfs is getting beyond the original topic in this bugzilla entry. This is a more general problem because there is no /sys/char directory. My current opinion is that it would be nice to see these attributes somewhere, but probably not worth the trouble. Kai -- Configure bugmail: http://bugzilla.kernel.org/userprefs.cgi?tab=email ------- You are receiving this mail because: ------- You are the assignee for the bug.-- To unsubscribe from this list: 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
