[Xen-devel] [PATCH for-4.5] libxl: remove existence check for PCI device hotplug

[Wei Liu <wei.liu2@xxxxxxxxxx>]

The existence check is to make sure a device is not added to a guest
multiple times.

PCI device backend path has different rules from vif, disk etc. For
example:
/local/domain/0/backend/pci/9/0/dev-1/0000:03:10.1
/local/domain/0/backend/pci/9/0/key-1/0000:03:10.1
/local/domain/0/backend/pci/9/0/dev-2/0000:03:10.2
/local/domain/0/backend/pci/9/0/key-2/0000:03:10.2

The devid for PCI devices is hardcoded 0. libxl__device_exists only
checks up to /local/.../9/0 so it always returns true even the device is
assignable.

Remove invocation of libxl__device_exists. We're sure at this point that
the PCI device is assignable (hence no xenstore entry or JSON entry).
The check is done before hand. For HVM guest it's done by calling
xc_test_assign_device and for PV guest it's done by calling
pciback_dev_is_assigned.

Reported-by: Li, Liang Z <liang.z.li@xxxxxxxxx>
Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>
Cc: Ian Campbell <ian.campbell@xxxxxxxxxx>
Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
Cc: Konrad Wilk <konrad.wilk@xxxxxxxxxx>
---
This patch fixes a regression in 4.5.

The risk is that I misunderstood semantics of xc_test_assign_device and
pciback_dev_is_assigned and end up adding several entries to JSON config
template. But if the assignable tests are incorrect I think we have a
bigger problem to worry about than duplicated entries in JSON template.

It would be good for someone to have PCI hotplug setup to run a quick test.  I
think Liang confirmed (indrectly) that xc_test_assign_device worked well for
him so I think there's won't be multiple JSON template entries for HVM guests.
However PV side still remains to be tested.
---
 tools/libxl/libxl_pci.c |    8 --------
 1 file changed, 8 deletions(-)

diff --git a/tools/libxl/libxl_pci.c b/tools/libxl/libxl_pci.c
index 9f40100..316643c 100644
--- a/tools/libxl/libxl_pci.c
+++ b/tools/libxl/libxl_pci.c
@@ -175,14 +175,6 @@ static int libxl__device_pci_add_xenstore(libxl__gc *gc, 
uint32_t domid, libxl_d
         rc = libxl__xs_transaction_start(gc, &t);
         if (rc) goto out;
 
-        rc = libxl__device_exists(gc, t, device);
-        if (rc < 0) goto out;
-        if (rc == 1) {
-            LOG(ERROR, "device already exists in xenstore");
-            rc = ERROR_DEVICE_EXISTS;
-            goto out;
-        }
-
         rc = libxl__set_domain_configuration(gc, domid, &d_config);
         if (rc) goto out;
 
-- 
1.7.10.4


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