On Tue, 24 Mar 2020 at 02:34, Theodore Y. Ts'o <ty...@mit.edu> wrote: > Another possibility, which would be messier for qemu, would be use a > flag set via fcntl. That would require qemu from noticing when the > guest is calling open, openat, or openat2, and then inserting a fcntl > system call to set the 32-bit readdir mode. That's cleaner from the > kernel interface complexity perspective, but it's messier for qemu.
On the contrary, that would be a much better interface for QEMU. We always know when we're doing an open-syscall on behalf of the guest, and it would be trivial to make the fcntl() call then. That would ensure that we don't accidentally get the '32-bit semantics' on file descriptors QEMU opens for its own purposes, and wouldn't leave us open to the risk in future that setting the PER_LINUX32 flag for all of QEMU causes unexpected extra behaviour in future kernels that would be correct for the guest binary but wrong/broken for QEMU's own internals. thanks -- PMM
