On 08/24/2017 07:23 AM, Erik Skultety wrote:
Adjust udevEventHandleThread to be a proper thread routine running in an infinite loop handling devices. Also introduce udevEventThreadData private structure. Every time there's and incoming event from udev, udevEventHandleCallback only increments the number of events queuing on the monitor and signals the worker thread to handle them.
Signed-off-by: Erik Skultety <eskultet@redhat.com> --- src/node_device/node_device_udev.c | 132 ++++++++++++++++++++++++++++++------- 1 file changed, 108 insertions(+), 24 deletions(-)
Once we get here I'm not sure I understand the udev interaction. I guess it's not "crystal clear" that the socket relationship is a queue of device events. I also haven't studied the udev code nor have I been working through this as much as you have lately - so perhaps something you've uncovered will help educate me in this manner. Still here's my thoughts and a small sliver of investigative data... So far there's been a 1-to-1 interaction between libvirt and udev event. With this change there could be an n-to-1 interaction - as in receive @n devices. Up to this point the interaction has been: 1. udev event 2. validate fd/udev_monitor 3. call udev_monitor_receive_device to get @device 4. process @device 5. unref @device 6. return to udev After this point 1. udev event 2. validate fd/udev_monitor 3. increase event count 4. signal condition to thread to wakeup 5. return to udev asynchronously in a loop 1. wakeup on condition and for each 'event' refcnt 2. decrease event refcnt 3. validate fd/udev_monitor 4. call udev_monitor_receive_device to get @device 5. process @device 6. unref @device If there's more than one event, does udev_monitor_receive_device guarantee the order? Are we sure udev buffers/queues in this manner? That is since we're not grabbing @device before we return to udev when the event is signaled, is there any guarantee from udev that *the same* device will still exist when we do get around to making our call? My concern being how "long" is the data guaranteed to be there. As I read the subsequent patch - I'm thinking perhaps we really want to keep that 1-to-1 relationship. Could the reason that you're getting those messages be because we're now calling udev out of the order it expected? Do we know why we're getting a NULL return? I found: https://sourcecodebrowser.com/udev/141/libudev-monitor_8c.html which seems to indicate a number of reasons to return NULL... Maybe udev is processing another device and while doing so it blocks anyone calling udev_monitor_receive_device. Conversely while processing an event that same block wouldn't be present because the expectation is that the called function will call udev_monitor_receive_device. I think perhaps the processing thread is fine to have; however, instead of processing the event it's processing an @device that was managed in udevEventHandleCallback and put onto some "worker queue". At least that way we know we have a refcnt'd udev_device and we can process in an expected order. John
diff --git a/src/node_device/node_device_udev.c b/src/node_device/node_device_udev.c index fe943c78b..444e5be4d 100644 --- a/src/node_device/node_device_udev.c +++ b/src/node_device/node_device_udev.c @@ -59,6 +59,54 @@ struct _udevPrivate { bool privileged; };
+typedef struct _udevEventThreadData udevEventThreadData; +typedef udevEventThreadData *udevEventThreadDataPtr; + +struct _udevEventThreadData { + virMutex lock; + virCond threadCond; + + bool threadQuit; + int monitor_fd; + unsigned long long nevents; /* number of udev events queuing on monitor */ +}; + + +static udevEventThreadDataPtr +udevEventThreadDataNew(int fd) +{ + udevEventThreadDataPtr ret = NULL; + + if (VIR_ALLOC_QUIET(ret) < 0) + return NULL; + + if (virMutexInit(&ret->lock) < 0) + goto cleanup; + + if (virCondInit(&ret->threadCond) < 0) + goto cleanup_mutex; + + ret->monitor_fd = fd; + + return ret; + + cleanup_mutex: + virMutexDestroy(&ret->lock); + + cleanup: + VIR_FREE(ret); + return NULL; +} + + +static void +udevEventThreadDataFree(udevEventThreadDataPtr data) +{ + virMutexDestroy(&data->lock); + virCondDestroy(&data->threadCond); + VIR_FREE(data); +} +
static bool udevHasDeviceProperty(struct udev_device *dev, @@ -1647,35 +1695,53 @@ udevCheckMonitorFD(struct udev_monitor *udev_monitor, int fd)
static void -udevEventHandleThread(void *opaque ATTRIBUTE_UNUSED) +udevEventHandleThread(void *opaque) { + udevEventThreadDataPtr privateData = opaque; struct udev_device *device = NULL; struct udev_monitor *udev_monitor = NULL; - int fd = (intptr_t) opaque;
- nodeDeviceLock(); - udev_monitor = DRV_STATE_UDEV_MONITOR(driver); + /* continue rather than break from the loop on non-fatal errors */ + while (1) { + virMutexLock(&privateData->lock); + while (privateData->nevents == 0 && !privateData->threadQuit) { + if (virCondWait(&privateData->threadCond, &privateData->lock)) { + virReportSystemError(errno, "%s", + _("handler failed to wait on condition")); + goto cleanup; + } + }
- if (!udevCheckMonitorFD(udev_monitor, fd)) - goto unlock; + privateData->nevents--; + virMutexUnlock(&privateData->lock);
- device = udev_monitor_receive_device(udev_monitor); - if (device == NULL) { - virReportError(VIR_ERR_INTERNAL_ERROR, "%s", - _("udev_monitor_receive_device returned NULL")); - goto unlock; + nodeDeviceLock(); + udev_monitor = DRV_STATE_UDEV_MONITOR(driver); + + if (!udevCheckMonitorFD(udev_monitor, privateData->monitor_fd)) { + nodeDeviceUnlock(); + goto cleanup; + } + + device = udev_monitor_receive_device(udev_monitor); + nodeDeviceUnlock(); + + if (!device) { + virReportError(VIR_ERR_INTERNAL_ERROR, "%s", + _("udev_monitor_receive_device returned NULL")); + goto next; + } + + udevHandleOneDevice(device); + + next: + udev_device_unref(device); }
- nodeDeviceUnlock(); - udevHandleOneDevice(device); - cleanup: udev_device_unref(device); + udevEventThreadDataFree(privateData); return; - - unlock: - nodeDeviceUnlock(); - goto cleanup; }
@@ -1683,20 +1749,28 @@ static void udevEventHandleCallback(int watch ATTRIBUTE_UNUSED, int fd, int events ATTRIBUTE_UNUSED, - void *data ATTRIBUTE_UNUSED) + void *opaque) { struct udev_monitor *udev_monitor = NULL; + udevEventThreadDataPtr threadData = opaque;
nodeDeviceLock(); udev_monitor = DRV_STATE_UDEV_MONITOR(driver); - if (!udevCheckMonitorFD(udev_monitor, fd)) { + virMutexLock(&threadData->lock); + threadData->threadQuit = true; + virCondSignal(&threadData->threadCond); + virMutexUnlock(&threadData->lock); + nodeDeviceUnlock(); return; } nodeDeviceUnlock();
- udevEventHandleThread((void *)(intptr_t) fd); + virMutexLock(&threadData->lock); + threadData->nevents++; + virCondSignal(&threadData->threadCond); + virMutexUnlock(&threadData->lock); }
@@ -1823,6 +1897,9 @@ nodeStateInitialize(bool privileged, { udevPrivate *priv = NULL; struct udev *udev = NULL; + int monitor_fd = -1; + virThread th; + udevEventThreadDataPtr threadData = NULL;
if (VIR_ALLOC(priv) < 0) return -1; @@ -1883,6 +1960,14 @@ nodeStateInitialize(bool privileged, 128 * 1024 * 1024); #endif
+ monitor_fd = udev_monitor_get_fd(priv->udev_monitor); + if (!(threadData = udevEventThreadDataNew(monitor_fd)) || + virThreadCreate(&th, false, udevEventHandleThread, threadData) < 0) { + virReportSystemError(errno, "%s", + _("failed to create udev handling thread")); + goto cleanup; + } + /* We register the monitor with the event callback so we are * notified by udev of device changes before we enumerate existing * devices because libvirt will simply recreate the device if we @@ -1891,9 +1976,8 @@ nodeStateInitialize(bool privileged, * enumeration. The alternative is to register the callback after * we enumerate, in which case we will fail to create any devices * that appear while the enumeration is taking place. */ - priv->watch = virEventAddHandle(udev_monitor_get_fd(priv->udev_monitor), - VIR_EVENT_HANDLE_READABLE, - udevEventHandleCallback, NULL, NULL); + priv->watch = virEventAddHandle(monitor_fd, VIR_EVENT_HANDLE_READABLE, + udevEventHandleCallback, threadData, NULL); if (priv->watch == -1) goto unlock;