Commit ff8adbcf authored by Tomoki Sekiyama's avatar Tomoki Sekiyama Committed by Michael Roth
Browse files

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: default avatarTomoki Sekiyama <tomoki.sekiyama@hds.com>
Reviewed-by: default avatarGal Hammer <ghammer@redhat.com>
Reviewed-by: default avatarYan Vugenfirer <yvugenfi@redhat.com>
Signed-off-by: default avatarMichael Roth <mdroth@linux.vnet.ibm.com>
parent 4c1b8f1e

qga/vss-win32/provider.cpp

+10 −1
Original line number Diff line number Diff line
@@ -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;

}

qga/vss-win32/requester.cpp

+26 −26
Original line number Diff line number Diff line
@@ -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