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qga: vss-win32: Fix interference with snapshot creation by other VSS requesters 

When a VSS requester such as vshadow.exe or diskshadow.exe requests to
create disk snapshots, Windows may choose qemu-ga VSS provider if it is
only provider registered on the system. However, because it provides only a
function to freeze the filesystem, the snapshotting fails.

This patch adds a check into CQGAVssProvider::IsVolumeSupported() to reject
the request from other VSS requesters, so that the other provider is chosen.

The check of requester is done by confirming event channels between
qemu-ga's requester and provider established. To ensure that the events are
initialized when CQGAVssProvider::IsVolumeSupported() is called, it moves
the initialization earlier.

Signed-off-by: Tomoki Sekiyama <tomoki.sekiyama@hds.com>
Reviewed-by: Gal Hammer <ghammer@redhat.com>
Reviewed-by: Yan Vugenfirer <yvugenfi@redhat.com>
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
This commit is contained in:
Tomoki Sekiyama 2014-01-13 12:25:29 -05:00 committed by Michael Roth
parent 4c1b8f1e83
commit ff8adbcfdb
2 changed files with 36 additions and 27 deletions
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11
qga/vss-win32/provider.cpp
View File

@ -291,8 +291,17 @@ STDMETHODIMP CQGAVssProvider::BeginPrepareSnapshot(
STDMETHODIMP CQGAVssProvider::IsVolumeSupported(
VSS_PWSZ pwszVolumeName, BOOL *pbSupportedByThisProvider)
{
*pbSupportedByThisProvider = TRUE;
HANDLE hEventFrozen;
/* Check if a requester is qemu-ga by whether an event is created */
hEventFrozen = OpenEvent(EVENT_ALL_ACCESS, FALSE, EVENT_NAME_FROZEN);
if (!hEventFrozen) {
*pbSupportedByThisProvider = FALSE;
return S_OK;
}
CloseHandle(hEventFrozen);
*pbSupportedByThisProvider = TRUE;
return S_OK;
}

52
qga/vss-win32/requester.cpp
View File

@ -252,6 +252,32 @@ void requester_freeze(int *num_vols, ErrorSet *errset)
CoInitialize(NULL);
/* Allow unrestricted access to events */
InitializeSecurityDescriptor(&sd, SECURITY_DESCRIPTOR_REVISION);
SetSecurityDescriptorDacl(&sd, TRUE, NULL, FALSE);
sa.nLength = sizeof(sa);
sa.lpSecurityDescriptor = &sd;
sa.bInheritHandle = FALSE;
vss_ctx.hEventFrozen = CreateEvent(&sa, TRUE, FALSE, EVENT_NAME_FROZEN);
if (!vss_ctx.hEventFrozen) {
err_set(errset, GetLastError(), "failed to create event %s",
EVENT_NAME_FROZEN);
goto out;
}
vss_ctx.hEventThaw = CreateEvent(&sa, TRUE, FALSE, EVENT_NAME_THAW);
if (!vss_ctx.hEventThaw) {
err_set(errset, GetLastError(), "failed to create event %s",
EVENT_NAME_THAW);
goto out;
}
vss_ctx.hEventTimeout = CreateEvent(&sa, TRUE, FALSE, EVENT_NAME_TIMEOUT);
if (!vss_ctx.hEventTimeout) {
err_set(errset, GetLastError(), "failed to create event %s",
EVENT_NAME_TIMEOUT);
goto out;
}
assert(pCreateVssBackupComponents != NULL);
hr = pCreateVssBackupComponents(&vss_ctx.pVssbc);
if (FAILED(hr)) {
@ -362,32 +388,6 @@ void requester_freeze(int *num_vols, ErrorSet *errset)
goto out;
}
/* Allow unrestricted access to events */
InitializeSecurityDescriptor(&sd, SECURITY_DESCRIPTOR_REVISION);
SetSecurityDescriptorDacl(&sd, TRUE, NULL, FALSE);
sa.nLength = sizeof(sa);
sa.lpSecurityDescriptor = &sd;
sa.bInheritHandle = FALSE;
vss_ctx.hEventFrozen = CreateEvent(&sa, TRUE, FALSE, EVENT_NAME_FROZEN);
if (!vss_ctx.hEventFrozen) {
err_set(errset, GetLastError(), "failed to create event %s",
EVENT_NAME_FROZEN);
goto out;
}
vss_ctx.hEventThaw = CreateEvent(&sa, TRUE, FALSE, EVENT_NAME_THAW);
if (!vss_ctx.hEventThaw) {
err_set(errset, GetLastError(), "failed to create event %s",
EVENT_NAME_THAW);
goto out;
}
vss_ctx.hEventTimeout = CreateEvent(&sa, TRUE, FALSE, EVENT_NAME_TIMEOUT);
if (!vss_ctx.hEventTimeout) {
err_set(errset, GetLastError(), "failed to create event %s",
EVENT_NAME_TIMEOUT);
goto out;
}
/*
* Start VSS quiescing operations.
* CQGAVssProvider::CommitSnapshots will kick vss_ctx.hEventFrozen