qga/commands-posix: Fix bug in guest-fstrim

The FITRIM ioctl updates the fstrim_range structure it receives. This
way the caller can determine how many bytes were trimmed. The
guest-fstrim logic reuses the same fstrim_range for each filesystem,
effectively limiting each filesystem to trim at most as much as the
previous was able to trim.

If a previous filesystem would have trimmed 0 bytes, than the next
filesystem would report an error 'Invalid argument' because a FITRIM
request with length 0 is not valid.

This change resets the fstrim_range structure for each filesystem.

Signed-off-by: Justin Ossevoort <justin@quarantainenet.nl>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>

qga/commands-posix.c

@@ -1332,11 +1332,7 @@ void qmp_guest_fstrim(bool has_minimum, int64_t minimum, Error **errp)
     struct FsMount *mount;
     int fd;
     Error *local_err = NULL;
-    struct fstrim_range r = {
-        .start = 0,
-        .len = -1,
-        .minlen = has_minimum ? minimum : 0,
-    };
+    struct fstrim_range r;
 
     slog("guest-fstrim called");
 
@@ -1360,6 +1356,9 @@ void qmp_guest_fstrim(bool has_minimum, int64_t minimum, Error **errp)
          * error means an unexpected error, so return it in those cases.  In
          * some other cases ENOTTY will be reported (e.g. CD-ROMs).
          */
+        r.start = 0;
+        r.len = -1;
+        r.minlen = has_minimum ? minimum : 0;
         ret = ioctl(fd, FITRIM, &r);
         if (ret == -1) {
             if (errno != ENOTTY && errno != EOPNOTSUPP) {