Improve performance and functionality of the bitstring(3) api

Two new functions are provided, bit_ffs_at() and bit_ffc_at(), which allow
for efficient searching of set or cleared bits starting from any bit offset
within the bit string.

Performance is improved by operating on longs instead of bytes and using
ffsl() for searches within a long. ffsl() is a compiler builtin in both
clang and gcc for most architectures, converting what was a brute force
while loop search into a couple of instructions.

All of the bitstring(3) API continues to be contained in the header file.
Some of the functions are large enough that perhaps they should be uninlined
and moved to a library, but that is beyond the scope of this commit.

sys/sys/bitstring.h:
        Convert the majority of the existing bit string implementation from
        macros to inline functions.

        Properly protect the implementation from inadvertant macro expansion
        when included in a user's program by prefixing all private
        macros/functions and local variables with '_'.

        Add bit_ffs_at() and bit_ffc_at(). Implement bit_ffs() and
        bit_ffc() in terms of their "at" counterparts.

        Provide a kernel implementation of bit_alloc(), making the full API
        usable in the kernel.

        Improve code documenation.

share/man/man3/bitstring.3:
        Add pre-exisiting API bit_ffc() to the synopsis.

        Document new APIs.

        Document the initialization state of the bit strings
        allocated/declared by bit_alloc() and bit_decl().

        Correct documentation for bitstr_size(). The original code comments
        indicate the size is in bytes, not "elements of bitstr_t". The new
        implementation follows this lead. Only hastd assumed "elements"
        rather than bytes and it has been corrected.

etc/mtree/BSD.tests.dist:
tests/sys/Makefile:
tests/sys/sys/Makefile:
tests/sys/sys/bitstring.c:
        Add tests for all existing and new functionality.

include/bitstring.h
	Include all headers needed by sys/bitstring.h

lib/libbluetooth/bluetooth.h:
usr.sbin/bluetooth/hccontrol/le.c:
        Include bitstring.h instead of sys/bitstring.h.

sbin/hastd/activemap.c:
        Correct usage of bitstr_size().

sys/dev/xen/blkback/blkback.c
        Use new bit_alloc.

sys/kern/subr_unit.c:
        Remove hard-coded assumption that sizeof(bitstr_t) is 1.  Get rid of
        unrb.busy, which caches the number of bits set in unrb.map.  When
        INVARIANTS are disabled, nothing needs to know that information.
        callapse_unr can be adapted to use bit_ffs and bit_ffc instead.
        Eliminating unrb.busy saves memory, simplifies the code, and
        provides a slight speedup when INVARIANTS are disabled.

sys/net/flowtable.c:
        Use the new kernel implementation of bit-alloc, instead of hacking
        the old libc-dependent macro.

sys/sys/param.h
        Update __FreeBSD_version to indicate availability of new API

Submitted by:   gibbs, asomers
Reviewed by:    gibbs, ngie
MFC after:      4 weeks
Sponsored by:   Spectra Logic Corp
Differential Revision:  https://reviews.freebsd.org/D6004

1 files changed, 95 insertions, 19 deletions

diff --git a/share/man/man3/bitstring.3 b/share/man/man3/bitstring.3
index 89a9524..f2dbb81 100644
--- a/share/man/man3/bitstring.3
+++ b/share/man/man3/bitstring.3
@@ -27,23 +27,54 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
+.\" Copyright (c) 2014 Spectra Logic Corporation
+.\" All rights reserved.
+.\"
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice, this list of conditions, and the following disclaimer,
+.\"    without modification.
+.\" 2. Redistributions in binary form must reproduce at minimum a disclaimer
+.\"    substantially similar to the "NO WARRANTY" disclaimer below
+.\"    ("Disclaimer") and any redistribution must be conditioned upon
+.\"    including a substantially similar Disclaimer requirement for further
+.\"    binary redistribution.
+.\"
+.\" NO WARRANTY
+.\" THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+.\" "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+.\" LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR
+.\" A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+.\" HOLDERS OR CONTRIBUTORS BE LIABLE FOR SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+.\" STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
+.\" IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+.\" POSSIBILITY OF SUCH DAMAGES.
+.\"
 .\"     @(#)bitstring.3	8.1 (Berkeley) 7/19/93
 .\" $FreeBSD$
 .\"
-.Dd October 17, 2015
+.Dd May 4, 2016
 .Dt BITSTRING 3
 .Os
 .Sh NAME
 .Nm bit_alloc ,
 .Nm bit_clear ,
 .Nm bit_decl ,
+.Nm bit_ffc ,
 .Nm bit_ffs ,
+.Nm bit_ffc_at ,
+.Nm bit_ffs_at ,
 .Nm bit_nclear ,
 .Nm bit_nset ,
 .Nm bit_set ,
-.Nm bitstr_size ,
-.Nm bit_test
-.Nd bit-string manipulation macros
+.Nm bit_test ,
+.Nm bitstr_size
+.Nd bit-string manipulation functions and macros
 .Sh SYNOPSIS
 .In bitstring.h
 .Ft bitstr_t *
@@ -57,6 +88,10 @@
 .Ft void
 .Fn bit_ffs "bitstr_t *name" "int nbits" "int *value"
 .Ft void
+.Fn bit_ffc_at "bitstr_t *name" "int start" "int nbits" "int *value"
+.Ft void
+.Fn bit_ffs_at "bitstr_t *name" "int start" "int nbits" "int *value"
+.Ft void
 .Fn bit_nclear "bitstr_t *name" "int start" "int stop"
 .Ft void
 .Fn bit_nset "bitstr_t *name" "int start" "int stop"
@@ -69,7 +104,7 @@
 .Sh DESCRIPTION
 These macros operate on strings of bits.
 .Pp
-The macro
+The function
 .Fn bit_alloc
 returns a pointer of type
 .Dq Fa "bitstr_t *"
@@ -78,23 +113,31 @@ to sufficient space to store
 bits, or
 .Dv NULL
 if no space is available.
+If successful, the returned bit string is initialized with all bits cleared.
 .Pp
 The macro
 .Fn bit_decl
-allocates sufficient space to store
+declares a bit string with sufficient space to store
 .Fa nbits
-bits on the stack.
+bits.
+.Fn bit_decl
+may be used to include statically sized bit strings in structure
+definitions or to create bit strings on the stack.
+Users of this macro are responsible for initialization of the bit string,
+typically via a global initialization of the containing struct or use of the
+.Fn bit_nset
+or
+.Fn bin_nclear
+functions.
 .Pp
 The macro
 .Fn bitstr_size
-returns the number of elements of type
-.Fa bitstr_t
-necessary to store
+returns the number of bytes necessary to store
 .Fa nbits
 bits.
 This is useful for copying bit strings.
 .Pp
-The macros
+The functions
 .Fn bit_clear
 and
 .Fn bit_set
@@ -107,7 +150,7 @@ The
 .Fn bit_nset
 and
 .Fn bit_nclear
-macros
+functions
 set or clear the zero-based numbered bits from
 .Fa start
 through
@@ -117,16 +160,28 @@ in the bit string
 .Pp
 The
 .Fn bit_test
-macro
+function
 evaluates to non-zero if the zero-based numbered bit
 .Fa bit
 of bit string
 .Fa name
 is set, and zero otherwise.
 .Pp
+The function
+.Fn bit_ffc
+stores in the location referenced by
+.Fa value
+the zero-based number of the first bit not set in the array of
+.Fa nbits
+bits referenced by
+.Fa name .
+If all bits are set, the location referenced by
+.Fa value
+is set to \-1.
+.Pp
 The
 .Fn bit_ffs
-macro
+function
 stores in the location referenced by
 .Fa value
 the zero-based number of the first bit set in the array of
@@ -137,19 +192,40 @@ If no bits are set, the location referenced by
 .Fa value
 is set to \-1.
 .Pp
-The macro
-.Fn bit_ffc
+The function
+.Fn bit_ffc_at
 stores in the location referenced by
 .Fa value
 the zero-based number of the first bit not set in the array of
 .Fa nbits
 bits referenced by
-.Fa name .
-If all bits are set, the location referenced by
+.Fa name ,
+at or after the zero-based bit index
+.Fa start .
+If all bits at or after
+.Fa start
+are set, the location referenced by
+.Fa value
+is set to \-1.
+.Pp
+The
+.Fn bit_ffs_at
+function
+stores in the location referenced by
+.Fa value
+the zero-based number of the first bit set in the array of
+.Fa nbits
+bits referenced by
+.Fa name ,
+at or after the zero-based bit index
+.Fa start .
+If no bits are set after
+.Fa start ,
+the location referenced by
 .Fa value
 is set to \-1.
 .Pp
-The arguments to these macros are evaluated only once and may safely
+The arguments in bit string macros are evaluated only once and may safely
 have side effects.
 .Sh EXAMPLES
 .Bd -literal -offset indent