This bug is not upstream, and the define is too new to appear in debian. Upstream, AT_EMPTY_PATH is defined in io/fcntl.h. In debian, debian/patches/any/submitted-bits-fcntl_h-at.diff moves the *AT defines into the per-arch bits/fcntl.h files. The ubuntu-specific merge of newer upstream updated the patch doing so to remove the AT_EMPTY_PATH with the rest of that blcok from io/fcntl.c, but does not add it to the bits/fcntl.h files.
This is needed for qemu-kvm to compile the virtio-9p-handle.c file.
This bug is not upstream, and the define is too new to appear in debian. Upstream, AT_EMPTY_PATH is defined in io/fcntl.h. In debian, debian/ patches/ any/submitted- bits-fcntl_ h-at.diff moves the *AT defines into the per-arch bits/fcntl.h files. The ubuntu-specific merge of newer upstream updated the patch doing so to remove the AT_EMPTY_PATH with the rest of that blcok from io/fcntl.c, but does not add it to the bits/fcntl.h files.
This is needed for qemu-kvm to compile the virtio-9p-handle.c file.
A debdiff is attached which adds the definition.