Re: [Qemu-devel] [RFC PATCH v2 00/11] qemu-ga: fsfreeze on Windows using VSS

[Tomoki Sekiyama <tomoki.sekiyama@hds.com>]

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Hi,

On 4/23/13 12:44 , "Tomoki Sekiyama" <tomoki.sekiyama@hds.com> wrote:
>>    2 executing the command "{"execute":"guest-fsfreeze-freeze"}"
>>failed,the output is:
><snip>
>> {"execute":"guest-fsfreeze-freeze"}
>> {"error": {"class": "GenericError", "desc": "Failed to
>>pVssbc->SetContext. (Error: 8004231b) "}}
>> 
>> Could you give me some advise to debug this problem ? I can provide more
>>information if need.
>
>Is there any logs corresponding to the error in Event Viewer?
>
>And this might be caused by unsupported VSS_VOLSNAP_ATTR_* flags in
>SetContext()
>called from qga_vss_fsfreeze_freeze() at qga/vss-win32-requester.cpp,
>but I couldn't find out flags not supported on Windows 7 from VSS
>references.

I'm investigating this issue. Some versions of Windows seem to
ignore VSS_VOLSNAP_ATTR_NO_AUTORECOVERY, and to cause an error with
VSS_VOLSNAP_ATTR_TRANSPORTABLE. In such cases, we cannot disable
Auto-recovery that requires writable snapshots we don't yet support.
Because of this, even if we remove TRANSPORTABLE flag, auto-recovery
would be enabled and cause another error (VSS_E_OBJECT_NOT_FOUND) on thaw.

The patch attached (to be applied after v2 patch) removes TRANSPORTABLE
flag, and ignores the VSS_E_OBJECT_NOT_FOUND error on thaw.
I think this should resolve the issue in Windows 7, and also works in
the other versions of Windows. Could you try this?

If it works, I will merge this into my path set and resend it as v3.

Thanks,
Tomoki Sekiyama


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diff --git a/qga/vss-win32-requester.cpp b/qga/vss-win32-requester.cpp
index 90ff026..0e02818 100644
--- a/qga/vss-win32-requester.cpp
+++ b/qga/vss-win32-requester.cpp
@@ -259,12 +259,11 @@ void qga_vss_fsfreeze_freeze(int *num_vols, Error **err)
     /*
      * Currently writable snapshots are not supported.
      * To prevent the final commit (which requires to write to snapshots),
-     * VSS_VOLSNAP_ATTR_NO_AUTORECOVERY (for Win2008 SP2 or later) and
-     * VSS_VOLSNAP_ATTR_TRANSPORTABLE (for ealier versions) are specified here.
+     * VSS_VOLSNAP_ATTR_NO_AUTORECOVERY (for Win2008 SP2 or later) 
+     * are specified here.
      */
     chk( pVssbc->SetContext(VSS_CTX_APP_ROLLBACK |
                             VSS_VOLSNAP_ATTR_NO_AUTORECOVERY |
-                            VSS_VOLSNAP_ATTR_TRANSPORTABLE |
                             VSS_VOLSNAP_ATTR_TXF_RECOVERY) );
 
     chk( pVssbc->GatherWriterMetadata(&pAsync) );
@@ -372,7 +371,19 @@ void qga_vss_fsfreeze_thaw(int *num_vols, Error **err)
     assert(pVssbc);
     assert(pAsyncSnapshot);
 
-    _chk( WaitForAsync(pAsyncSnapshot), "DoSnapshotSet", err, out );
+    HRESULT hr = WaitForAsync(pAsyncSnapshot);
+    if (hr == VSS_E_OBJECT_NOT_FOUND) {
+        /*
+         * On Windows earlier than 2008 SP2 which does not support
+         * VSS_VOLSNAP_ATTR_NO_AUTORECOVERY context, final commit is not
+         * skipped and VSS is aborted. In this case, we get here. Still the
+         * snapshot is taken successfully, so we just ignore the error.
+         */
+        pAsyncSnapshot->Release();
+        pAsyncSnapshot = NULL;
+        goto final;
+    }
+    _chk( hr, "DoSnapshotSet", err, out );
     pAsyncSnapshot->Release();
     pAsyncSnapshot = NULL;
 
@@ -380,6 +391,7 @@ void qga_vss_fsfreeze_thaw(int *num_vols, Error **err)
     _chk( WaitForAsync(pAsync), "BackupComplete", err, out );
     pAsync->Release();
 
+final:
     *num_vols = cFrozenVols;
     cFrozenVols = 0;
     goto done;