Re: [PATCH] scsi: clear UAC before sending SG_IO

From: Douglas Gilbert
Date: Thu Sep 10 2020 - 13:51:58 EST

On 2020-09-10 6:15 a.m., Randall Huang wrote:
Make sure UAC is clear before sending SG_IO.

Signed-off-by: Randall Huang <huangrandall@xxxxxxxxxx>

This patch just looks wrong. Imagine if every LLD front loaded some LLD
specific code before each invocation of ioctl(SG_IO). Is UAC Unit Attention
Condition? If so the mid-level notes them as they fly past.

Haven't looked at the rest of the patchset but I suspect the "wlun_clr_uac"
work needs a rethink. If that is the REPORT LUNS Well known LUN then perhaps
it could be handled in the mid-level scanning code. Otherwise it should
be handled in the LLD/UFS.

Also users of ioctl(SG_IO) should be capable of handling UAs, even if they
are irrelevant, and repeat the invocation. Finally ioctl(sg_dev, SG_IO) is
not the only way to send a pass-through command, there are also
- write(sg_dev, ...)
- ioctl(bsg_dev, SG_IO, ...)
- ioctl(most_blk_devs, SG_IO, ...)
- ioctl(st_dev, SG_IO, ...)

Hopefully I have convinced you by now not to take this route.

Doug Gilbert

drivers/scsi/sg.c | 8 ++++++++
1 file changed, 8 insertions(+)

diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
index 20472aaaf630..ad11bca47ae8 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;
+ int _cmd;
SCSI_LOG_TIMEOUT(3, sg_printk(KERN_INFO, sdp,
"sg_ioctl: cmd=0x%x\n", (int) cmd_in));
@@ -933,6 +934,13 @@ sg_ioctl_common(struct file *filp, Sg_device *sdp, Sg_fd *sfp,
return -ENODEV;
if (!scsi_block_when_processing_errors(sdp->device))
return -ENXIO;
+ if (sdp->device->host->wlun_clr_uac) {
+ sdp->device->host->hostt->ioctl(sdp->device, _cmd, NULL);
+ sdp->device->host->wlun_clr_uac = false;
+ }
result = sg_new_write(sfp, filp, p, SZ_SG_IO_HDR,
1, read_only, 1, &srp);
if (result < 0)