On Mon, Apr 14 2008 at 13:50 +0300, FUJITA Tomonori <fujita.tomonori@xxxxxxxxxxxxx> wrote: > This patchset adds large command support to the block layer. > > We rarely handle large commands. So for optimization, a struct request > still has a static array for a command. rq_init sets rq->cmd pointer > to the static array. In short, rq_init() does > > rq->cmd = rq->__cmd; > > So we can access to rq->cmd and rq->cmd_len as before. > > Boaz argues that having single cmd_len is dangerous: > >> Because this way it is dangerous if large commands are issued to legacy >> drivers. In scsi-land we have .cmd_len at host template that will govern if >> we are allow to issue larger commands to the driver. In block devices we do >> not have such a facility, and the danger is if such commands are issued through >> bsg or other means, even by malicious code. What you say is the ideal and it > > I don't see how it is dangerous. We don't send large commands to block > devices via bsg. We can send large commands to block devices via only > SG_IO. SG_IO (block/scsi_ioctl.c) forbids us sending commands large > than 16 bytes, BLK_MAX_CDB. So how can we send large commands to block > devices? > > The first, second, and third patches are safe cleanups (a preparation > for changing rq->cmd from the static array to a pointer). They don't > conflict with Boaz's patchset. Even if we choose Boaz's approach now, > we'll move to the approach to have one command length in struct > request in the long term. So they can be applied now. > > The forth patch adds large command support. It's a substitute for > Boaz's second patch. It's pretty simple except for one hack for > ide-io. It's necessary since the ide subsystem allocates struct > request without using blk_get_request. In the long term, it would > better to convert it to use blk_get_request properly. > > I still think that my last patch with one cmd_len and the Union is nicer and more simple. And does not waist the extra pointer that is never ever used but by me. (And does not need 3 preparation patches) Boaz -- 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
