YASUOKA Masahiko <yasu...@openbsd.org> wrote: > Currently the value on VMware may be truncated silently. It's simply > broken. I think we should fix it by having a way to know if the value > is reached the limit. > > Also I think we should be able to pass larger size of data. Since at > least on VMware, people is useing for parameters when deployment > through OVF tamplate. Sometimes the parameter includes large data > like X.509 certificate. > > https://docs.vmware.com/en/VMware-vSphere/7.0/com.vmware.vsphere.vm_admin.doc/GUID-D0F9E3B9-B77B-4DEF-A982-49B9F6358FF3.html > > What do you think? > > > Prepare a variable like kern.maxpvbus and default it to > > 4096. Futhermore, how about free() after copyout() to user space? > > I suppose we can use the space prepared by the userland directly.
An example of this mechanism is SIOCGIFCONF. The ioctl passes a pointer to a struct containing length & pointer to data. See net/if.c ifconf() There are other similar schemes, but they all come down to asking the kernel for the size and then doing a 2nd ioctl. Or a 3rd or more calls, in case the value has changed in the meantime and grown even further, but userland can realloc() the storage until it wins.
