qga: minimal support for fstrim for Windows guests

Unfortunately, there is no public Windows API to start trimming the
filesystem. The only viable way here is to call 'defrag.exe /L' for
each volume.

This is working since Win8 and Win2k12.

Signed-off-by: Denis V. Lunev <den@openvz.org>
Signed-off-by: Denis Plotnikov <dplotnikov@virtuozzo.com>
CC: Michael Roth <mdroth@linux.vnet.ibm.com>
CC: Stefan Weil <sw@weilnetz.de>
CC: Marc-André Lureau <marcandre.lureau@gmail.com>
* check g_utf16_to_utf8() return value for GError handling instead
  of GError directly (Marc-André)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>

qga/commands-win32.c

@@ -840,10 +840,101 @@ static void guest_fsfreeze_cleanup(void)
 GuestFilesystemTrimResponse *
 qmp_guest_fstrim(bool has_minimum, int64_t minimum, Error **errp)
 {
-    error_setg(errp, QERR_UNSUPPORTED);
+    GuestFilesystemTrimResponse *resp;
+    HANDLE handle;
+    WCHAR guid[MAX_PATH] = L"";
+
+    handle = FindFirstVolumeW(guid, ARRAYSIZE(guid));
+    if (handle == INVALID_HANDLE_VALUE) {
+        error_setg_win32(errp, GetLastError(), "failed to find any volume");
         return NULL;
     }
 
+    resp = g_new0(GuestFilesystemTrimResponse, 1);
+
+    do {
+        GuestFilesystemTrimResult *res;
+        GuestFilesystemTrimResultList *list;
+        PWCHAR uc_path;
+        DWORD char_count = 0;
+        char *path, *out;
+        GError *gerr = NULL;
+        gchar * argv[4];
+
+        GetVolumePathNamesForVolumeNameW(guid, NULL, 0, &char_count);
+
+        if (GetLastError() != ERROR_MORE_DATA) {
+            continue;
+        }
+        if (GetDriveTypeW(guid) != DRIVE_FIXED) {
+            continue;
+        }
+
+        uc_path = g_malloc(sizeof(WCHAR) * char_count);
+        if (!GetVolumePathNamesForVolumeNameW(guid, uc_path, char_count,
+                                              &char_count) || !*uc_path) {
+            /* strange, but this condition could be faced even with size == 2 */
+            g_free(uc_path);
+            continue;
+        }
+
+        res = g_new0(GuestFilesystemTrimResult, 1);
+
+        path = g_utf16_to_utf8(uc_path, char_count, NULL, NULL, &gerr);
+
+        g_free(uc_path);
+
+        if (!path) {
+            res->has_error = true;
+            res->error = g_strdup(gerr->message);
+            g_error_free(gerr);
+            break;
+        }
+
+        res->path = path;
+
+        list = g_new0(GuestFilesystemTrimResultList, 1);
+        list->value = res;
+        list->next = resp->paths;
+
+        resp->paths = list;
+
+        memset(argv, 0, sizeof(argv));
+        argv[0] = (gchar *)"defrag.exe";
+        argv[1] = (gchar *)"/L";
+        argv[2] = path;
+
+        if (!g_spawn_sync(NULL, argv, NULL, G_SPAWN_SEARCH_PATH, NULL, NULL,
+                          &out /* stdout */, NULL /* stdin */,
+                          NULL, &gerr)) {
+            res->has_error = true;
+            res->error = g_strdup(gerr->message);
+            g_error_free(gerr);
+        } else {
+            /* defrag.exe is UGLY. Exit code is ALWAYS zero.
+               Error is reported in the output with something like
+               (x89000020) etc code in the stdout */
+
+            int i;
+            gchar **lines = g_strsplit(out, "\r\n", 0);
+            g_free(out);
+
+            for (i = 0; lines[i] != NULL; i++) {
+                if (g_strstr_len(lines[i], -1, "(0x") == NULL) {
+                    continue;
+                }
+                res->has_error = true;
+                res->error = g_strdup(lines[i]);
+                break;
+            }
+            g_strfreev(lines);
+        }
+    } while (FindNextVolumeW(handle, guid, ARRAYSIZE(guid)));
+
+    FindVolumeClose(handle);
+    return resp;
+}
+
 typedef enum {
     GUEST_SUSPEND_MODE_DISK,
     GUEST_SUSPEND_MODE_RAM
@@ -1416,7 +1507,7 @@ GList *ga_command_blacklist_init(GList *blacklist)
         "guest-get-memory-blocks", "guest-set-memory-blocks",
         "guest-get-memory-block-size",
         "guest-fsfreeze-freeze-list",
-        "guest-fstrim", NULL};
+        NULL};
     char **p = (char **)list_unsupported;
 
     while (*p) {