copyin() or copyout().
uvm_useracc() tells us whether the mapping permissions allow access to
the desired part of an address space, and many callers assume that
this is the same as knowing whether an attempt to access that part of
the address space will succeed. however, access to user space can
fail for reasons other than insufficient permission, most notably that
paging in any non-resident data can fail due to i/o errors. most of
the callers of uvm_useracc() make the above incorrect assumption. the
rest are all misguided optimizations, which optimize for the case
where an operation will fail. we'd rather optimize for operations
succeeding, in which case we should just attempt the access and handle
failures due to insufficient permissions the same way we handle i/o
errors. since there appear to be no good uses of uvm_useracc(), we'll
just remove it.
swapent, or as seen in userland, is dbtob(1), which turns to be 512 for all
arch for now.
In struct swapdev, there is another field for block size. This value is private
to uvm_swap.c and is only used for swap I/O on regular files. It is equal to
the underlying device block size and it is not necessarily 512.
- Added two more swapctl commands: GETFREESWAP and GETSWAPVIRT.
There is a problem in the way swap block size are found here. See comment
in get_block_size().
sys_swapctl(SWAP_STATS). This enable the use of a kernel based
buffer instead of using some temporary memory in the stackgap,
whereas we cannot make sure that the size os the struct swapent array
will fit in it. (it is not known at build time, but the stackgap len
is set at build time).
perry