Re: [libvirt] [PATCH] storage: Refresh storage pool after upload

On 07/29/2014 09:39 AM, Daniel P. Berrange wrote: > On Tue, Jul 29, 2014 at 03:28:33PM +0200, Peter Krempa wrote: >> On 07/28/14 15:24, John Ferlan wrote: >>> https://bugzilla.redhat.com/show_bug.cgi?id=1072653 >>> >>> Upon successful upload of a volume, the target volume and storage pool >>> were not updated to reflect any changes as a result of the upload. Make >>> use of the existing stream close callback mechanism to force a backend >>> pool refresh to occur once the stream closes. >>> >>> Signed-off-by: John Ferlan <jferlan(a)redhat.com&gt; >>> --- >>> src/libvirt.c | 8 +++++ >>> src/libvirt_private.syms | 1 + >>> src/storage/storage_driver.c | 78 ++++++++++++++++++++++++++++++++++++++++++++ >>> tools/virsh.pod | 3 ++ >>> 4 files changed, 90 insertions(+) >>> >>> diff --git a/src/libvirt.c b/src/libvirt.c >>> index 143d319..992e4f2 100644 >>> --- a/src/libvirt.c >>> +++ b/src/libvirt.c >>> @@ -13960,6 +13960,14 @@ virStorageVolDownload(virStorageVolPtr vol, >>> * detect any errors. The results will be unpredictable if >>> * another active stream is writing to the storage volume. >>> * >>> + * When the data stream is closed whether the upload is successful >>> + * or not the target storage pool will be refreshed to reflect pool >>> + * and volume changes as a result of the upload. Depending on >>> + * the target volume storage backend and the source stream type >>> + * for a successful upload, the target volume may take on the >>> + * characteristics from the source stream such as format type, >>> + * capacity, and allocation. >>> + * >>> * Returns 0, or -1 upon error. >>> */ >>> int >>> diff --git a/src/libvirt_private.syms b/src/libvirt_private.syms >>> index b1fb7c9..7ef68a1 100644 >>> --- a/src/libvirt_private.syms >>> +++ b/src/libvirt_private.syms >>> @@ -825,6 +825,7 @@ virFDStreamCreateFile; >>> virFDStreamOpen; >>> virFDStreamOpenFile; >>> virFDStreamOpenPTY; >>> +virFDStreamSetInternalCloseCb; >>> >>> >>> # libvirt_internal.h >>> diff --git a/src/storage/storage_driver.c b/src/storage/storage_driver.c >>> index efbe5ff..5fd5514 100644 >>> --- a/src/storage/storage_driver.c >>> +++ b/src/storage/storage_driver.c >>> @@ -59,6 +59,12 @@ static virStorageDriverStatePtr driverState; >>> >>> static int storageStateCleanup(void); >>> >>> +typedef struct _virStorageVolStreamInfo virStorageVolStreamInfo; >>> +typedef virStorageVolStreamInfo *virStorageVolStreamInfoPtr; >>> +struct _virStorageVolStreamInfo { >>> + char *pool_name; >>> +}; >>> + >>> static void storageDriverLock(virStorageDriverStatePtr driver) >>> { >>> virMutexLock(&driver->lock); >>> @@ -1956,6 +1962,52 @@ storageVolDownload(virStorageVolPtr obj, >>> } >>> >>> >>> +/** >>> + * Frees opaque data provided for the stream closing callback >>> + * >>> + * @opaque Data to be freed. >>> + */ >>> +static void virStorageVolFDStreamCloseCbFree(void *opaque) >>> +{ >>> + virStorageVolStreamInfoPtr cbdata = opaque; >>> + >>> + VIR_FREE(cbdata->pool_name); >>> + VIR_FREE(cbdata); >>> +} >>> + >>> +/** >>> + * Callback being called if a FDstream is closed. Frees device entries >>> + * from data structures and removes lockfiles. >>> + * >>> + * @st Pointer to stream being closed. >>> + * @opaque Domain's device information structure. >>> + */ >>> +static void virStorageVolFDStreamCloseCb(virStreamPtr st ATTRIBUTE_UNUSED, >>> + void *opaque) >>> +{ >>> + >>> + virStorageVolStreamInfoPtr cbdata = opaque; >>> + virStoragePoolObjPtr pool = NULL; >>> + virStorageBackendPtr backend; >>> + >>> + storageDriverLock(driverState); >> >> I'm a bit concerned about locking the storage driver here. This code >> will be called by the stream close callback which is handled from the >> event loop. While I don't currently see any problem, this instance could >> bite us in the future. > > The risk would be that some part of the storage driver holds the > lock, and needs to wait on some event from the event loop. That > could lead to a deadlock situation. In fact we could deadlock > ourselves if the 'refreshPool' function uses the event loop, which > is not entirely unlikely. Also, refreshing the storage pool size > can be a somewhat heavy (ie slow) operation for some of the storage > backends. > Would narrowing the window to just the virStoragePoolObjFindByName() work better? Don't think we need the lock once we have the pool by the passed name.

> I think I'd be inclined to say that the stream close callback > should spawn a throw-away thread to do the refresh work. This > avoids the deadlock risk and avoids blocking the event loop > for prolonged time. > The only other "consumer" of this stream close path is virChrdevOpen() and I believe that was for console support. So, by adding a throw-away thread that console code is impacted - something I'm hoping to avoid...