In particular the virt-rescue --scratch option makes it very easy to add huge numbers of drives. Since the per-backend max_disks limit was never checked anywhere you could get peculiar failures. Now you'll get a clear error message: $ virt-rescue --scratch=256 libguestfs: error: too many drives have been added, the current backend only supports 255 drives --- lib/launch.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+) diff --git a/lib/launch.c b/lib/launch.c index 7f06c69..37ab024 100644 --- a/lib/launch.c +++ b/lib/launch.c @@ -55,12 +55,27 @@ static struct backend { int guestfs_impl_launch (guestfs_h *g) { + int r; + /* Configured? */ if (g->state != CONFIG) { error (g, _("the libguestfs handle has already been launched")); return -1; } + /* Too many drives? + * + * Some backends such as ‘unix:’ don't allow us to query max_disks. + * Don't fail in this case. + */ + guestfs_push_error_handler (g, NULL, NULL); + r = guestfs_max_disks (g); + guestfs_pop_error_handler (g); + if (r >= 0 && g->nr_drives > (size_t) r) { + error (g, _("too many drives have been added, the current backend only supports %d drives"), r); + return -1; + } + /* Start the clock ... */ gettimeofday (&g->launch_t, NULL); TRACE0 (launch_start); -- 2.9.3