While implementing a vhost-user-blk driver for libblkio, I found some problems with VHOST_USER_ADD/REM_MEM_REG both in the spec and in the implementations in QEMU and libvhost-user that this series addresses.
I also noticed that you can use REM_MEM_REG or SET_MEM_TABLE to unmap a memory region that is still in use (e.g. a block I/O request using addresses from the region has been started, but not completed yet), which is not great. I'm not sure how to fix this best, though. We would have to wait for these requests to complete (maybe introduce a refcount and wait for it to drop to zero), but waiting seems impossible in libvhost-user because it doesn't have any main loop integration. Just failing the memory region removal would be safe, but potentially a rather awkward interface because clients would have to implement some retry logic. Kevin Wolf (3): docs/vhost-user: Clarifications for VHOST_USER_ADD/REM_MEM_REG libvhost-user: Fix extra vu_add/rem_mem_reg reply vhost-user: Don't pass file descriptor for VHOST_USER_REM_MEM_REG docs/interop/vhost-user.rst | 17 +++++++++++++++++ hw/virtio/vhost-user.c | 2 +- subprojects/libvhost-user/libvhost-user.c | 17 +++++++---------- 3 files changed, 25 insertions(+), 11 deletions(-) -- 2.35.1
