porting tmpfs

[Alex Hornung]

Good to hear from you again!

> Also I don’t understand why Alex Hornung has removed tmpfs_spec_vnops.
> Without adding this ops call to mknod() ends with panic. (I have to
> run fsstress with option “–f mknod=0”.)

In short, because of devfs. mknod is not needed, and shouldn't be
used, as nodes created with it won't work anyways.

> Next I tried to use objcache instead of plain kmalloc() to allocate
> tmpfs nodes and direntries. Â But when objcache is destroyed during
> unmount, there is a crit_panic "td_pri is/would-go negative! -26"
> caused by mag_purge() calling crit_exit() at objcache.c. It seems that
> mag_purge() is not called from the critical section as it is expected.