On Tuesday 20 May 2008, FUJITA Tomonori wrote: > The goal of this patchset is reverting the commit > 22a9189fd073db3d03a4cf8b8c098aa207602de1 (cdrom: use kmalloced buffers > instead of buffers on stack). > > http://lkml.org/lkml/2008/4/21/634 > > The commit is using kmalloced buffers for cdrom packet commands to > avoid stack corruption on non coherent platforms. But allocating a > small buffer like this is not nice (unnecessary complicity): > > + buffer = kmalloc(8, GFP_KERNEL); > > I tried to remove generic_packet() and convert cdrom users to use the > block queue like pkt_generic_packet (as Jens suggested in the thread > if I correctly understand), but it turned out that it needs tricky > surgery (like handling ssleep and retries for packet commands in ide). > > Then I found that we can easily handle packet commands on non coherent > platforms. The diffstat is pretty small except for the revert. All > this patchset does is just setting the dma_pad_mask to > ARCH_KMALLOC_MINALIGN. > > Only scsi and ide-cd do DMA generic_packet. In the case of scsi, > sr_packet uses blk_rq_map_kern (the commit > 68154e90c9d1492d570671ae181d9a8f8530da55) post 2.6.25. So if we set > the dma padding on non coherent platforms, sr_packet uses allocated > pages properly. > > In the case of IDE, ide-cd has a mechanism to handle alignment and > padding for SG_IO. So we can easily exploit it for packet commands. > > If some architectures can't do DMA on stack, we also need to a new > queue_flag like QUEUE_FLAG_NO_DMA_ON_STACK in addtion of this > patchset. > > The diffstat is: > > block/blk-settings.c | 30 +++++- > drivers/ata/libata-scsi.c | 3 +- > drivers/cdrom/cdrom.c | 274 +++++++++++++++------------------------------ > drivers/ide/ide-cd.c | 17 ++- > include/linux/blkdev.h | 1 + > 5 files changed, 134 insertions(+), 191 deletions(-) The patchset looks good to me after a quick look but Borislav is a more appropriate person to contact on ide-cd specific patches. Thanks, Bart -- 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
