Re: [PATCH 2/2] vfio-ccw: support async command subregion

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On 26/11/2018 10:58, Cornelia Huck wrote:
On Fri, 23 Nov 2018 15:13:12 +0100
Pierre Morel <pmorel@xxxxxxxxxxxxx> wrote:

On 22/11/2018 17:54, Cornelia Huck wrote:
A vfio-ccw device may provide an async command subregion for
issuing halt/clear subchannel requests. If it is present, use
it for sending halt/clear request to the device; if not, fall
back to emulation (as done today).

Signed-off-by: Cornelia Huck <cohuck@xxxxxxxxxx>
---
   hw/s390x/css.c              |  27 +++++++--
   hw/vfio/ccw.c               | 109 +++++++++++++++++++++++++++++++++++-
   include/hw/s390x/s390-ccw.h |   3 +
   3 files changed, 133 insertions(+), 6 deletions(-)


@@ -114,6 +120,87 @@ again:
       }
   }
+int vfio_ccw_handle_clear(SubchDev *sch)
+{
+    S390CCWDevice *cdev = sch->driver_data;
+    VFIOCCWDevice *vcdev = DO_UPCAST(VFIOCCWDevice, cdev, cdev);
+    struct ccw_cmd_region *region = vcdev->async_cmd_region;
+    int ret;
+
+    if (!vcdev->async_cmd_region) {
+        /* Async command region not available, fall back to emulation */
+        return -ENOSYS;
+    }
+
+    memset(region, 0, sizeof(*region));
+    region->command = VFIO_CCW_ASYNC_CMD_CSCH;
+
+again:
+    ret = pwrite(vcdev->vdev.fd, region,
+                 vcdev->async_cmd_region_size, vcdev->async_cmd_region_offset);
+    if (ret != vcdev->async_cmd_region_size) {
+        if (errno == EAGAIN) {


Where do the EAGAIN come from?

It might be set by pwrite.

I saw that the man indicate this, and so we are legitimate to handle the fail case, but I did not find EAGAIN in the path of the write for accessing devices and I did not find it in the access to the CSS.

If we do not set it explicitly from the driver, the concern I have is: isn't it dangerous to try again and shouldn't we better abort?





+            goto again;
+        }
+        error_report("vfio-ccw: wirte I/O region failed with errno=%d", errno);

I should also fix up this message here and for hsch as well :)

+        ret = -errno;
+    } else {
+        ret = region->ret_code;
+    }
+    switch (ret) {
+    case 0:
+    case -ENODEV:
+    case -EACCES:

should never happen?

It should not happen; but it can nevertheless be returned, so...

I understand: nothing to clear :)




+        return 0;
+    case -EFAULT:
+    default:
+        sch_gen_unit_exception(sch);
+        css_inject_io_interrupt(sch);
+        return 0;
+    }
+}
+

otherwise LGTM

Thanks!







--
Pierre Morel
Linux/KVM/QEMU in Böblingen - Germany




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