bitmask_snprintf(9) - NetBSD Manual Pages

BITMASK_SNPRINTF(9)    NetBSD Kernel Developer's Manual    BITMASK_SNPRINTF(9)


NAME

     bitmask_snprintf -- bitmask output conversion


SYNOPSIS

     #include <sys/systm.h>

     char *
     bitmask_snprintf(u_quad_t val, const char *fmt, char *buf,
         size_t buflen);


DESCRIPTION

     The bitmask_snprintf() function formats a bitmask into a mnemonic form
     suitable for printing.

     This conversion is useful for decoding bit fields in device registers.
     It formats the integer val into the buffer buf, of size buflen, using a
     specified radix and an interpretation of the bits within that integer as
     though they were flags.

     The decoding directive string fmt describes how the bitfield is to be
     interpreted and displayed.  It follows two possible syntaxes, referred to
     as ``old'' and ``new''.  The main advantage of the ``new'' formatting is
     that it is capable of handling multi-bit fields.

     The first character of fmt may be \177, indicating that the remainder of
     the format string follows the ``new'' syntax.  The second character (the
     first for the old format) is a binary character representation of the
     output numeral base in which the bitfield will be printed before it is
     decoded.  Recognized radix values (in C escape-character format) are \10
     (octal), \12 (decimal), and \20 (hexadecimal).

     The remaining characters in fmt are interpreted as a list of bit-posi-
     tion-description pairs.  From here the syntaxes diverge.

     The ``old'' format syntax is series of bit-position-description pairs.
     Each begins with a binary character value that represents the position of
     the bit being described.  A bit position value of one describes the least
     significant bit.  Whereas a position value of 32 (octal 40, hexadecimal
     20, the ASCII space character) describes the most significant bit.

     The remaining characters in a bit-position-description pair are the char-
     acters to print should the bit being described be set.  Description
     strings are delimited by the next bit position value character encoun-
     tered (distinguishable by its value being <= 32), or the end of the
     decoding directive string itself.

     For the ``new'' format syntax, a bit-position-description begins with a
     field type followed by a binary bit-position and possibly a field length.
     The least significant bit is bit-position zero, unlike the ``old'' syntax
     where it is one.

     b\B    Describes a bit position.  The bit-position B indicates the corre-
            sponding bit, as in the ``old'' format.

     f\B\L  Describes a multi-bit field beginning at bit-position B and having
            a bit-length of L.  The remaining characters are printed as a
            description of the field followed by `=' and the value of the
            field.  The value of the field is printed in the base specified as
            the second character of the decoding directive string fmt.

     F\B\L  Describes a multi-bit field like `f', but just extracts the value
            for use with the `=' and `:' formatting directives described
            below.

     =\V    The field previously extracted by the last `f' or `F' operator is
            compared to the byte `V' (for values 0 through 255).  If they are
            equal, `=' followed by the string following `V' is printed.  This
            and the `:' operator may be repeated to annotate multiple possible
            values.

     :\V    Operates like the `=' operator, but omits the leading `='.

     Finally, each field is delimited by a NUL (`\0') character.  By conven-
     tion, the format string has an additional NUL character at the end, fol-
     lowing that delimiting the last bit-position-description pair.

     The buffer buf passed to bitmask_snprintf must be at least
     KPRINTF_BUFSIZE bytes in length.  See the source code for the definition
     of this macro.


RETURN VALUES

     The bitmask_snprintf() function returns the buffer buf.  The returned
     string is always NULL-terminated.


EXAMPLES

     Two examples of the old formatting style:

           bitmask_snprintf(3, "\10\2BITTWO\1BITONE", buf, buflen)
           => "3<BITTWO,BITONE>"

           bitmask_snprintf(0xe860,
                  "\20\x10NOTBOOT\x0fFPP\x0eSDVMA\x0cVIDEO"
                  "\x0bLORES\x0aFPA\x09DIAG\x07CACHE"
                  "\x06IOCACHE\x05LOOPBACK\x04DBGCACHE",
                   buf, buflen)
           => "e860<NOTBOOT,FPP,SDVMA,VIDEO,CACHE,IOCACHE>"

     An example of the new formatting style:

           bitmask_snprintf(0x800f0701,
                  "\177\020b\0LSB\0b\1_BITONE\0f\4\4NIBBLE2\0"
                  "f\x10\4BURST\0=\4FOUR\0=\xfSIXTEEN\0"
                  "b\x1fMSB\0\0",
                   buf, buflen)
           => "800f0701<LSB,NIBBLE2=0,BURST=f=SIXTEEN,MSB>"


ERRORS

     If the buffer buf is too small to hold the formatted output,
     bitmask_snprintf() will still return the buffer, containing a truncated
     string.


SEE ALSO

     printf(9)


CODE REFERENCES

     sys/kern/subr_prf_bitmask.c


HISTORY

     The bitmask_snprintf() function was originally implemented as a non-stan-
     dard %b format string for the kernel printf() function in NetBSD 1.5 and
     earlier releases.


AUTHORS

     The ``new'' format was the invention of Chris Torek.

NetBSD 5.0                       July 29, 2007                      NetBSD 5.0