On Thu, 2008-01-31 at 18:41 +0100, Geert Uytterhoeven wrote: > On Thu, 31 Jan 2008, Nicholas A. Bellinger wrote: > > On Thu, 2008-01-31 at 10:26 -0600, James Bottomley wrote: > > > On Thu, 2008-01-31 at 08:10 -0800, Nicholas A. Bellinger wrote: > > > > On Thu, 2008-01-31 at 09:34 -0600, James Bottomley wrote: > > > > > On Thu, 2008-01-31 at 06:10 -0800, Nicholas A. Bellinger wrote: > > > > > > Greetings Geert and Co, > > > > > > > > > > > > I have a related patch that I have been using with ps3rom.c for some > > > > > > time that fixes a bug in fs/bio.c that assumes 512 byte sectors for > > > > > > ATAPI operations. This bug actually exists for all non 512 byte sector > > > > > > devices go through this code path (I found it with > > > > > > scsi_execute_async()), but I first ran into this issue with ps3rom.c > > > > > > because max_sectors (32) is small enough to trigger the bug assuming 512 > > > > > > byte sectors during typical ATAPI READ_10 ops with iSCSI/HD. Because > > > > > > typical max_sector settings for libata and USB are much higher, I have > > > > > > never ran into this issue outside of ps3rom.c, but the bug exists > > > > > > nevertheless.. > > > > > > > > > > > > The current patch assumes 512 byte sectors, and adds a sector_size > > > > > > parameter to drivers/scsi/scsi_lib.c:scsi_req_map_sg() to change it for > > > > > > passed struct request. I know that some folks talked about killing > > > > > > scsi_execute_async() and fixing this problem elsewhere, but until then > > > > > > please consider this patch. Any input is also appreciated. > > > > > > > > > > My first reaction is really, no; there's no way we should be doing such > > > > > a nasty layering violation. > > > > > > > > > > > > > I don't care for it either, but without this patch (or something > > > > similar) all SCSI targets that use scsi_execute_async(), for non 512 > > > > byte requests are broken. This causes a problem when a small max_sector > > > > is correctly used by the LLD, and trips the check in > > > > fs/bio.c:__bio_add_page() > > > > > > > > if (((bio->bi_size + len) >> 9) > max_sectors) > > > > > > > > > > Could we rewind this discussion back to an actual problem description > > > then, please? Nothing in the standard path for a CD/DVD should be using > > > scsi_execute_async(), what's the actual problem use case? > > > > > > > The problem case is a SCSI Target Mode engine that receives a 2048 Byte > > single sector ATAPI READ_10 request from the storage fabric, and uses > > scsi_execute_async() (the only option >= 2.6.18) to issue said request > > to the underlying struct scsi_device. Because the underlying bio code > > assumes 512 byte only sectors, the check in __bio_add_page() incorrectly > > determines that max_sectors (max_sectors has to be low, as with 32 from > > ps3rom.c) has been exceeded, and fails the request back up the stack. > > Thanks for unfocussing James ;-) > > James, do you have any comment about the first email in this thread, increasing > scsi_host_template.max_sectors? Assuming your BOUNCE_SIZE is in bytes, and represents your largest transfer, then yes, setting .max_sectors to BOUNCE_SIZE>>9 is exactly the right way of phrasing this, since .max_sectors is counted in units of the internal block sector (or 512 bytes). Were you going to submit a full patch to linux-scsi? James - 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
