On Mon, Apr 15, 2024 at 3:28 PM Yongji Xie <xieyon...@bytedance.com> wrote: > > On Sun, Apr 14, 2024 at 5:02 PM Michael S. Tsirkin <m...@redhat.com> wrote: > > > > On Fri, Apr 12, 2024 at 12:15:40PM +0200, Eugenio Perez Martin wrote: > > > Hi! > > > > > > I'm building a bridge to expose vhost-user devices through VDUSE. The > > > code is still immature but I'm able to forward packets using > > > dpdk-l2fwd through VDUSE to VM. I'm now developing exposing virtiofsd, > > > but I've hit an error I'd like to discuss. > > > > > > VDUSE devices can get all the memory regions the driver is using by > > > VDUSE_IOTLB_GET_FD ioctl. It returns a file descriptor with a memory > > > region associated that can be mapped with mmap, and an information > > > entry about the map it contains: > > > * Start and end addresses from the driver POV > > > * Offset within the mmaped region of these start and end > > > * Device permissions over that region. > > > > > > [start=0xc3000][last=0xe7fff][offset=0xc3000][perm=1] > > > > > > Now when I try to map it, it is impossible for the userspace device to > > > call mmap with any offset different than 0. > > > > How exactly did you allocate memory? hugetlbfs? > > > > > So the "straightforward" > > > mmap with size = entry.last-entry.start and offset = entry.offset does > > > not work. I don't know if this is a limitation of Linux or VDUSE. > > > > > > Checking QEMU's > > > subprojects/libvduse/libvduse.c:vduse_iova_add_region() I see it > > > handles the offset by adding it up to the size, instead of using it > > > directly as a parameter in the mmap: > > > > > > void *mmap_addr = mmap(0, size + offset, prot, MAP_SHARED, fd, 0); > > > > > > CC Xie Yongji who wrote this code, too. > > > > The mmap() with hugetlb would fail if the offset into the file is not > aligned to the huge page size. So libvhost-user did something like > this. But I think VDUSE doesn't have this problem.
I think what you meant is that VDUSE IOTLB doesn't have this problem. Btw, I think we need to understand the setup. E.g is this used for containers (bounce pages) or VM (hugetlb or other). Thanks > So it's fine to > directly use the offset as a parameter in the mmap(2) here. > > Thanks, > Yongji >
