vfio: fix race condition with sysfs

[ upstream commit b758423 ]

This fix treats a 0 return value from vfio_open_group_fd
in vfio_get_group_fd as the intended error condition instead
of putting an incorrect 0 file descriptor in the vfio_group table.

Sometimes, the creation of device files in sysfs is not
instantaneously causing vfio_open_groupfd to return 0.
This has been observed when hot removing/adding multiple
NVMe devices (>=4).

Fixes: 340b7bb ("vfio: extend data structure for multi container")

Signed-off-by: Michael Haeuptle <michael.haeuptle@hpe.com>
Acked-by: Darek Stojaczyk <dariusz.stojaczyk@intel.com>
Acked-by: Anatoly Burakov <anatoly.burakov@intel.com>

lib/librte_eal/linuxapp/eal/eal_vfio.c

@@ -378,7 +378,7 @@ vfio_get_group_fd(struct vfio_config *vfio_cfg,
 	}
 
 	vfio_group_fd = vfio_open_group_fd(iommu_group_num);
-	if (vfio_group_fd < 0) {
+	if (vfio_group_fd <= 0) {
 		RTE_LOG(ERR, EAL, "Failed to open group %d\n", iommu_group_num);
 		return -1;
 	}