macros, __BIT, __BITS, SHIFTIN, SHIFTOUT, and __arraycount() from
lib/libkern/libkern.h to sys/cdefs.h. Add a __-prefix to SHIFTIN
and SHIFTOUT, and add a manual page for the bit-twiddling macros,
bits(3).
Make the __BIT and __BITS macros "widthless," as best I can, by
changing their type to uintmax_t from uint32_t. XXX The manual
page lags this change by a bit.
Define __PRIxBIT and __PRIxBITS printf(3) format strings.
counting the number of elements in a static array, using the idiom,
sizeof(array)/sizeof(array[0]).
XXX This may move in the future, but this is a safe place to put
XXX it for use in the kernel.
FROMBCD()/TOBCD() macros into wrappers around it, resulting in both
smaller code footprint and elimination of possible issues due to
multiple evaluation of macro arguments.
Suggested by Simon Burge and Anders Gavare on tech-kern.
I had duplicated them. Improve the macros' names. Simplify their
implementation.
A brief description of each macro is below.
BIT(n): Return a bitmask with bit m set, where the least
significant bit is bit 0.
BITS(m, n): Return a bitmask with bits m through n, inclusive,
set. It does not matter whether m>n or m<=n.
The least significant bit is bit 0.
A "bitfield" is a span of consecutive bits defined by a
bitmask, where 1s select the bits in the bitfield. SHIFTIN,
SHIFTOUT, and SHIFTOUT_MASK help read and write bitfields
from device registers.
SHIFTIN(v, mask): Left-shift bits `v' into the bitfield
defined by `mask', and return them. No
side-effects.
SHIFTOUT(v, mask): Extract and return the bitfield selected
by `mask' from `v', right-shifting the
bits so that the rightmost selected bit
is at bit 0. No side-effects.
SHIFTOUT_MASK(mask): Right-shift the bits in `mask' so that
the rightmost non-zero bit is at bit
0. This is useful for finding the
greatest unsigned value that a bitfield
can hold. No side-effects. Note that
SHIFTOUT_MASK(m) = SHIFTOUT(m, m).
Examples:
/*
* Register definitions taken from the RFMD RF3000 manual.
*/
#define RF3000_GAINCTL 0x11 /* TX variable gain control */
#define RF3000_GAINCTL_TXVGC_MASK BITS(7, 2)
#define RF3000_GAINCTL_SCRAMBLER BIT(1)
/*
* Shift the transmit power into the transmit-power field of the
* gain-control register and write it to the baseband processor.
*/
atw_rf3000_write(sc, RF3000_GAINCTL,
SHIFTIN(txpower, RF3000_GAINCTL_TXVGC_MASK));
/*
* Register definitions taken from the ADMtek ADM8211 manual.
*
*/
#define ATW_RXSTAT_OWN BIT(31) /* 1: NIC may fill descriptor */
/* ... */
#define ATW_RXSTAT_DA1 BIT(17) /* DA bit 1, admin'd address */
#define ATW_RXSTAT_DA0 BIT(16) /* DA bit 0, group address */
#define ATW_RXSTAT_RXDR_MASK BITS(15,12) /* RX data rate */
#define ATW_RXSTAT_FL_MASK BITS(11,0) /* RX frame length, last
* descriptor only
*/
/* Extract the frame length from the Rx descriptor's
* status field.
*/
len = SHIFTOUT(rxstat, ATW_RXSTAT_FL_MASK);
particular problem on hosts with only wireless interfaces that are
definitely not safe to use as entropy sources.
Add arc4randbytes() which hands out bytes from the same source used
by arc4random(). This is intended to be a _temporary_ interface
until we can design and implement a better general PRNG interface
that is decoupled from the entropy-pool implementation.
Modify key_randomfill() (used only for initialization vectors on
SA creation and via key_sa_stir_iv(), which does not "stir",
despite its name) to use arc4randbytes() instead of pulling bits
directly from the entropy pool. It is my hope that this change
will pose minimal integration problems for the KAME folks as the
random-pool interface is *already* different between each BSD
variant; this just simplifies the NetBSD case and solves a
fairly serious problem.
Note that it is generally considered acceptable cryptographic
practice to use a fast stream cipher to generate IVs for encryption
with stronger block ciphers. For example, the use of "non-Approved"
PRNGs to generate IVs for "Approved" block ciphers is explicitly
sanctioned by FIPS 140-2.
