----- Original Message ----- > From: "Laurence Oberman" <lober...@redhat.com> > To: dgilb...@interlog.com, "Linux SCSI List" <linux-scsi@vger.kernel.org> > Sent: Wednesday, March 1, 2017 10:44:32 AM > Subject: sg driver, sg_io and sg tablesize > > Hi Doug > I have a quick question here regarding the sg tablesize and retrieval of the > supported size via a userspace ioctl. > > lpfc defaults to > lpfc_sg_seg_cnt:Max Scatter Gather Segment Count (uint) = 64 > > For sg_io sent from qemu if we exceed 512K I/O we fail, qlogic allows 128 by > default. > > 7:0:2:13 /dev/sdbb 67:80 /dev/sg55 Emulex lpfc LUN > > [root@dhcp40-131 ~]# sg_dd if=/dev/zero of=/dev/sdbb bpt=0x400 count=0x400 > blk_sgio=1 > Assume default 'bs' (block size) of 512 bytes > writing (SG_IO) on sg device, error: Invalid argument > sg_write failed, seek=0 > Some error occurred, remaining block count=1024 > 1024+0 records in > 0+0 records out > > 9:0:1:13 /dev/sdcm 71:240 /dev/sg92 Qlogic qla2xxx LUN > > [root@dhcp40-131 ~]# sg_dd if=/dev/zero of=/dev/sdcm bpt=0x400 count=0x400 > blk_sgio=1 > Assume default 'bs' (block size) of 512 bytes > 1024+0 records in > 1024+0 records out > > Using ioctl(sg_fd, BLKSECTGET, &max_sectors) from userspace correctly returns > the /sys/block/sdcm/queue/max_sectors_kb > > How can we query the sg tablesize using a userspace ioctl for the sg driver. > > Figured I would ask you first. > > Thanks > Laurence >
Answering my own email, I chatted with Ewan and we decided we would point our Virt/Qemu team to simply go after max_segments in sysfs This was suggested by Ewan and is the best way to know what the actual max I/O size for sg_io would be for the LPFC driver. Thanks Laurence
