It was my concern as well, that for this sort of "backwards-incompatible reason", it has been kept broken intentionally. I am not sure if queue_max_sectors() or BLKSECTGET has ever been implemented in the block layer to give out the limit in bytes, but it certainly isn't the case anymore. I am not in position to say whether it's "right" or "wrong" to implement BLKSECTGET/BLKSSZGET in the sg driver, but they is definitely useful in some cases (as long as the queue_* functions work for the given underlying device). Is it not okay if they don't ultimately work on *some* devices, even when they aren't named SG_*? Perhaps we can consider having them removed as well (and implement them as e.g. SG_GET_MAX_SECTORS and SG_GET_LBS; but IMHO that only makes a point if they can be made to work on more than block devices). On Sun, 6 Sep 2020 at 04:37, Douglas Gilbert <dgilbert@xxxxxxxxxxxx> wrote: > > On 2020-09-05 3:32 p.m., Bart Van Assche wrote: > > On 2020-09-04 13:05, Tom Yan wrote: > >> It should give out the maximum number of sectors per request > >> instead of maximum number of bytes. > >> > >> Signed-off-by: Tom Yan <tom.ty89@xxxxxxxxx> > >> --- > >> drivers/scsi/sg.c | 6 ++++-- > >> 1 file changed, 4 insertions(+), 2 deletions(-) > >> > >> diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c > >> index 20472aaaf630..e57831910228 100644 > >> --- a/drivers/scsi/sg.c > >> +++ b/drivers/scsi/sg.c > >> @@ -922,6 +922,7 @@ sg_ioctl_common(struct file *filp, Sg_device *sdp, Sg_fd *sfp, > >> int result, val, read_only; > >> Sg_request *srp; > >> unsigned long iflags; > >> + unsigned int max_sectors; > >> > >> SCSI_LOG_TIMEOUT(3, sg_printk(KERN_INFO, sdp, > >> "sg_ioctl: cmd=0x%x\n", (int) cmd_in)); > >> @@ -1114,8 +1115,9 @@ sg_ioctl_common(struct file *filp, Sg_device *sdp, Sg_fd *sfp, > >> sdp->sgdebug = (char) val; > >> return 0; > >> case BLKSECTGET: > >> - return put_user(max_sectors_bytes(sdp->device->request_queue), > >> - ip); > >> + max_sectors = min_t(unsigned int, USHRT_MAX, > >> + queue_max_sectors(sdp->device->request_queue)); > >> + return put_user(max_sectors, ip); > >> case BLKTRACESETUP: > >> return blk_trace_setup(sdp->device->request_queue, > >> sdp->disk->disk_name, > > > > Is this perhaps a backwards-incompatible change to the kernel ABI, the > > kind of change Linus totally disagrees with? > > > > Additionally, please Cc linux-api for patches that modify the kernel ABI. > >>From https://www.kernel.org/doc/man-pages/linux-api-ml.html: "The kernel > > source file Documentation/SubmitChecklist notes that all Linux kernel > > patches that change userspace interfaces should be CCed to > > linux-api@xxxxxxxxxxxxxxx, so that the various parties who are interested > > in API changes are informed. For further information, see > > https://www.kernel.org/doc/man-pages/linux-api-ml.html"; > > Hmm, > The BLK* ioctl()s in the sg driver were an undocumented addition by others. > Plus it is not clear to me why a char device such as the sg driver should > be supporting BLK* ioctl(2)s. For example, how should an enclosure react to > those ioctls or a WLUN? > > If they are going to be supported for storage devices and /dev/sdb and > /dev/sg2 are the same device then if: > blockdev --getmaxsect /dev/sg1 > > gives a different result to: > blockdev --getmaxsect /dev/sdb > > then I would consider that a bug. So fixing it is making the kernel ABI > more consistent :-) That's exactly my point. They should work identically as the ones implemented in the block layer, because of their names. With that said, sg_version needs to be bumped once the fix gets in, so that there's a way to differentiate the "different implementations" in userspace. > > Doug Gilbert > > > Regards, Tom
