On Mon, Aug 10, 2009 at 11:32:00AM -0400, Alan Stern wrote: > > > Is there some reason for not accounting for the 4 header bytes in the > > > allocation length value stored in the CDB? Or is this simply a bug? > > > > Um, we do. > > > > unsigned char *scsi_get_vpd_page(struct scsi_device *sdev, u8 page) > > unsigned char *buf = kmalloc(259, GFP_KERNEL); > > result = scsi_vpd_inquiry(sdev, buf, 0, 255); > > for (i = 0; i < buf[3]; i++) > > if (buf[i + 4] == page) > > goto found; > > buf = kmalloc(len + 4, GFP_KERNEL); > > result = scsi_vpd_inquiry(sdev, buf, page, len); > > I'm not referring to this routine; I'm talking about the code in > scsi_vpd_inquiry() where the CDB is set. You could have been a little clearer in your bug report. > > > Were you aware that SCSI-2 defines the allocation length to be a single > > > byte? cmd[3] is specified as "Reserved" in the spec. Hence the value > > > of "len" should be capped at 255 if sdev->scsi_level <= SCSI_2, right? > > > > and 'Reserved' in SCSI-2 means: > > > > "A reserved bit, field, or byte shall be set to zero, or in accordance > > with a future extension to this standard." (7.1.1) > > Sure. But what reason could there possibly be for making a field > non-zero when you know that the device won't be able to interpret the > value correctly? The fact that sdev->scsi_level == SCSI_2 means > the device follows _this_ version of the standard, not a future > extension. Or am I missing something? Because with my misunderstanding of the allocation length to be the page length, we wouldn't ever request more than 255 bytes until the device said it supported a page which is more than 255 bytes long. Since such a device must be outside the SCSI-2 spec, it was assumed to understand the meaning of the 'reserved' byte. So that wasn't a bug. Now that we need to pass 259 to get 255 bytes, that would be a bug, so we need to take care of it. > (And there's no reason to be rude. I'm trying to hold a civil > discussion.) It didn't feel like it. -- Matthew Wilcox Intel Open Source Technology Centre "Bill, look, we understand that you're interested in selling us this operating system, but compare it to ours. We can't possibly take such a retrograde step." -- 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
