[libvirt] [PATCH v5 6/6] nodedev: Work around the uevent race by hooking up virFileWaitForAccess

If we find ourselves in the situation that the 'add' uevent has been fired earlier than the sysfs tree for a device was created, we should use the best-effort approach and give kernel some predetermined amount of time, thus waiting for the attributes to be ready rather than discarding the device from our device list forever. If those don't appear in the given time frame, we need to move on, since libvirt can't wait indefinitely. Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1463285 Signed-off-by: Erik Skultety <eskultet(a)redhat.com&gt; --- src/node_device/node_device_udev.c | 16 +++++++++++++++- 1 file changed, 15 insertions(+), 1 deletion(-) diff --git a/src/node_device/node_device_udev.c b/src/node_device/node_device_udev.c index a6d7e6d70..0329cac90 100644 --- a/src/node_device/node_device_udev.c +++ b/src/node_device/node_device_udev.c @@ -1198,9 +1198,23 @@ udevProcessMediatedDevice(struct udev_device *dev, char *canonicalpath = NULL; virNodeDevCapMdevPtr data = &def->caps->data.mdev; - if (virAsprintf(&linkpath, "%s/mdev_type", udev_device_get_syspath(dev)) < 0) + /* Because of a kernel uevent race, we might get the 'add' event prior to + * the sysfs tree being ready, so any attempt to access any sysfs attribute + * would result in ENOENT and us dropping the device, so let's work around + * it by waiting for the attributes to become available. + */ + + if (virAsprintf(&linkpath, "%s/mdev_type", + udev_device_get_syspath(dev)) < 0) goto cleanup; + if (virFileWaitForExists(linkpath, 1, 100) < 0) { + virReportSystemError(errno, + _("failed to wait for file '%s' to appear"), + linkpath); + goto cleanup; + } + if (virFileResolveLink(linkpath, &canonicalpath) < 0) { virReportSystemError(errno, _("failed to resolve '%s'"), linkpath); goto cleanup; -- 2.13.6