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Annotation of src/lib/libc/gen/getcap.3, Revision 1.3

1.1       cgd         1: .\" Copyright (c) 1992 The Regents of the University of California.
                      2: .\" All rights reserved.
                      3: .\"
                      4: .\" This code is derived from software contributed to Berkeley by
                      5: .\" Casey Leedom of Lawrence Livermore National Laboratory.
                      6: .\"
                      7: .\" Redistribution and use in source and binary forms, with or without
                      8: .\" modification, are permitted provided that the following conditions
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                     10: .\" 1. Redistributions of source code must retain the above copyright
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                     12: .\" 2. Redistributions in binary form must reproduce the above copyright
                     13: .\"    notice, this list of conditions and the following disclaimer in the
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                     15: .\" 3. All advertising materials mentioning features or use of this software
                     16: .\"    must display the following acknowledgement:
                     17: .\"    This product includes software developed by the University of
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                     23: .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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1.2       mycroft    35: .\"    from: @(#)getcap.3      5.4 (Berkeley) 8/11/92
1.3     ! jtc        36: .\"    $Id: getcap.3,v 1.2 1993/07/30 08:36:09 mycroft Exp $
1.1       cgd        37: .\"
                     38: .Dd "August 11, 1992"
                     39: .Dt GETCAP 3
                     40: .Os
                     41: .Sh NAME
                     42: .Nm cgetent ,
                     43: .Nm cgetset ,
                     44: .Nm cgetmatch ,
                     45: .Nm cgetcap ,
                     46: .Nm cgetnum ,
                     47: .Nm cgetstr ,
                     48: .Nm cgetustr ,
                     49: .Nm cgetfirst ,
                     50: .Nm cgetnext ,
                     51: .Nm cgetclose
                     52: .Nd capability database access routines
                     53: .Sh SYNOPSIS
                     54: .Fd #include <stdlib.h>
                     55: .Ft int
                     56: .Fn cgetent "char **buf" "char **db_array" "char *name"
                     57: .Ft int
                     58: .Fn cgetset "char *ent"
                     59: .Ft int
                     60: .Fn cgetmatch "char *buf" "char *name"
                     61: .Ft char *
                     62: .Fn cgetcap "char *buf" "char *cap" "char type"
                     63: .Ft int
                     64: .Fn cgetnum "char *buf" "char *cap" "long *num"
                     65: .Ft int
                     66: .Fn cgetstr "char *buf" "char *cap" "char **str"
                     67: .Ft int
                     68: .Fn cgetustr "char *buf" "char *cap" "char **str"
                     69: .Ft int
                     70: .Fn cgetfirst "char **buf" "char **db_array"
                     71: .Ft int
                     72: .Fn cgetnext "char **buf" "char **db_array"
                     73: .Ft int
                     74: .Fn cgetclose "void"
                     75: .Sh DESCRIPTION
                     76: .Fn Cgetent
                     77: extracts the capability rec
                     78: .Fa name
                     79: from the database specified by the
                     80: .Dv NULL
                     81: terminated file array
                     82: .Fa db_array
                     83: and returns a pointer to a
                     84: .Xr malloc Ns \&'d
                     85: copy of it in
                     86: .Fa buf .
                     87: .Nm Cgetent
                     88: will first look for files ending in
                     89: .Nm .db
                     90: (see
                     91: .Xr cap_mkdb 1)
                     92: before accessing the ASCII file.
                     93: .Fa Buf
                     94: must be retained through all subsequent calls to
                     95: .Fn cgetmatch ,
                     96: .Fn cgetcap ,
                     97: .Fn cgetnum ,
                     98: .Fn cgetstr ,
                     99: and
                    100: .Fn cgetustr ,
                    101: but may then be
                    102: .Xr free Ns \&'d.
                    103: On success 0 is returned, 1 if the returned
                    104: record contains an unresolved
                    105: .Nm tc
                    106: expansion,
                    107: \-1 if the requested record couldn't be found,
                    108: \-2 if a system error was encountered (couldn't open/read a file, etc.) also
                    109: setting
                    110: .Va errno ,
                    111: and \-3 if a potential reference loop is detected (see
                    112: .Ic tc=
                    113: comments below).
                    114: .Pp
                    115: .Nm Cgetset
                    116: enables the addition of a character buffer containing a single capability
                    117: record entry
                    118: to the capability database.
                    119: Conceptually, the entry is added as the first ``file'' in the database, and
                    120: is therefore searched first on the call to
                    121: .Nm cgetent .
                    122: The entry is passed in
                    123: .Fa ent .
                    124: If
                    125: .Fa ent
                    126: is
                    127: .Dv NULL ,
                    128: the current entry is removed from the database.
                    129: .Nm Cgetset
                    130: must precede the database traversal.  It must be called before the
                    131: .Nm cgetent
                    132: call. If a sequential access is being performed (see below), it must be called
                    133: before the first sequential access call (
                    134: .Nm cgetfirst
                    135: or
                    136: .Nm cgetnext
                    137: ), or be directly preceded by a
                    138: .Nm cgetclose
                    139: call.
                    140: On success 0 is returned and \-1 on failure.
                    141: .Pp
                    142: .Nm Cgetmatch
                    143: will return 0 if
                    144: .Fa name
                    145: is one of the names of the capability record
                    146: .Fa buf ,
                    147: \-1 if
                    148: not.
                    149: .Pp
                    150: .Nm Cgetcap
                    151: searches the capability record
                    152: .Fa buf
                    153: for the capability
                    154: .Fa cap
                    155: with type
                    156: .Fa type .
                    157: A
                    158: .Fa type
                    159: is specified using any single character.  If a colon (`:') is used, an
                    160: untyped capability will be searched for (see below for explanation of
                    161: types).  A pointer to the value of
                    162: .Fa cap
                    163: in
                    164: .Fa buf
                    165: is returned on success,
                    166: .Dv NULL
                    167: if the requested capability couldn't be
                    168: found.  The end of the capability value is signaled by a `:' or
                    169: .Tn ASCII
                    170: .Dv NUL
                    171: (see below for capability database syntax).
                    172: .Pp
                    173: .Nm Cgetnum
                    174: retrieves the value of the numeric capability
                    175: .Fa cap
                    176: from the capability record pointed to by
                    177: .Fa buf .
                    178: The numeric value is returned in the
                    179: .Ft long
                    180: pointed to by
                    181: .Fa num .
                    182: 0 is returned on success, \-1 if the requested numeric capability couldn't
                    183: be found.
                    184: .Pp
                    185: .Nm Cgetstr
                    186: retrieves the value of the string capability
                    187: .Fa cap
                    188: from the capability record pointed to by
                    189: .Fa buf .
                    190: A pointer to a decoded,
                    191: .Dv NUL
                    192: terminated,
                    193: .Xr malloc Ns \&'d
                    194: copy of the string is returned in the
                    195: .Ft char *
                    196: pointed to by
                    197: .Fa str .
                    198: The number of characters in the decoded string not including the trailing
                    199: .Dv NUL
                    200: is returned on success, \-1 if the requested string capability couldn't
                    201: be found, \-2 if a system error was encountered (storage allocation
                    202: failure).
                    203: .Pp
                    204: .Nm Cgetustr
                    205: is identical to
                    206: .Nm cgetstr
                    207: except that it does not expand special characters, but rather returns each
                    208: character of the capability string literally.
                    209: .Pp
                    210: .Nm Cgetfirst ,
                    211: .Nm cgetnext ,
                    212: comprise a function group that provides for sequential
                    213: access of the
                    214: .Dv NULL
                    215: pointer terminated array of file names,
                    216: .Fa db_array .
                    217: .Nm Cgetfirst
                    218: returns the first record in the database and resets the access
                    219: to the first record.
                    220: .Nm Cgetnext
                    221: returns the next record in the database with respect to the
                    222: record returned by the previous
                    223: .Nm cgetfirst
                    224: or
                    225: .Nm cgetnext
                    226: call.  If there is no such previous call, the first record in the database is
                    227: returned.
                    228: Each record is returned in a
                    229: .Xr malloc Ns \&'d
                    230: copy pointed to by
                    231: .Fa buf .
                    232: .Ic Tc
                    233: expansion is done (see
                    234: .Ic tc=
                    235: comments below).
                    236: Upon completion of the database 0 is returned,  1 is returned upon successful
                    237: return of record with possibly more remaining (we haven't reached the end of
                    238: the database yet), 2 is returned if the record contains an unresolved
                    239: .Nm tc
1.3     ! jtc       240: expansion, \-1 is returned if an system error occurred, and \-2
1.1       cgd       241: is returned if a potential reference loop is detected (see
                    242: .Ic tc=
                    243: comments below).
                    244: Upon completion of database (0 return) the database is closed.
                    245: .Pp
                    246: .Nm Cgetclose
                    247: closes the sequential access and frees any memory and file descriptors
                    248: being used.  Note that it does not erase the buffer pushed by a call to
                    249: .Nm cgetset .
                    250: .Sh CAPABILITY DATABASE SYNTAX
                    251: Capability databases are normally
                    252: .Tn ASCII
                    253: and may be edited with standard
                    254: text editors.  Blank lines and lines beginning with a `#' are comments
                    255: and are ignored.  Lines ending with a `\|\e' indicate that the next line
                    256: is a continuation of the current line; the `\|\e' and following newline
                    257: are ignored.  Long lines are usually continued onto several physical
                    258: lines by ending each line except the last with a `\|\e'.
                    259: .Pp
                    260: Capability databases consist of a series of records, one per logical
                    261: line.  Each record contains a variable number of `:'-separated fields
                    262: (capabilities).  Empty fields consisting entirely of white space
                    263: characters (spaces and tabs) are ignored.
                    264: .Pp
                    265: The first capability of each record specifies its names, separated by `|'
                    266: characters.  These names are used to reference records in the database.
                    267: By convention, the last name is usually a comment and is not intended as
                    268: a lookup tag.  For example, the
                    269: .Em vt100
                    270: record from the
                    271: .Nm termcap
                    272: database begins:
                    273: .Pp
                    274: .Dl "d0\||\|vt100\||\|vt100-am\||\|vt100am\||\|dec vt100:"
                    275: .Pp
                    276: giving four names that can be used to access the record.
                    277: .Pp
                    278: The remaining non-empty capabilities describe a set of (name, value)
                    279: bindings, consisting of a names optionally followed by a typed values:
                    280: .Bl -column "nameTvalue"
                    281: .It name Ta "typeless [boolean] capability"
                    282: .Em name No "is present [true]"
                    283: .It name Ns Em \&T Ns value Ta capability
                    284: .Pq Em name , \&T
                    285: has value
                    286: .Em value
                    287: .It name@ Ta "no capability" Em name No exists
                    288: .It name Ns Em T Ns \&@ Ta capability
                    289: .Pq Em name , T
                    290: does not exist
                    291: .El
                    292: .Pp
                    293: Names consist of one or more characters.  Names may contain any character
                    294: except `:', but it's usually best to restrict them to the printable
                    295: characters and avoid use of graphics like `#', `=', `%', `@', etc.  Types
                    296: are single characters used to separate capability names from their
                    297: associated typed values.  Types may be any character except a `:'.
                    298: Typically, graphics like `#', `=', `%', etc. are used.  Values may be any
                    299: number of characters and may contain any character except `:'.
                    300: .Sh CAPABILITY DATABASE SEMANTICS
                    301: Capability records describe a set of (name, value) bindings.  Names may
                    302: have multiple values bound to them.  Different values for a name are
                    303: distinguished by their
                    304: .Fa types .
                    305: .Nm Cgetcap
                    306: will return a pointer to a value of a name given the capability name and
                    307: the type of the value.
                    308: .Pp
                    309: The types `#' and `=' are conventionally used to denote numeric and
                    310: string typed values, but no restriction on those types is enforced.  The
                    311: functions
                    312: .Nm cgetnum
                    313: and
                    314: .Nm cgetstr
                    315: can be used to implement the traditional syntax and semantics of `#'
                    316: and `='.
                    317: Typeless capabilities are typically used to denote boolean objects with
                    318: presence or absence indicating truth and false values respectively.
                    319: This interpretation is conveniently represented by:
                    320: .Pp
                    321: .Dl "(getcap(buf, name, ':') != NULL)"
                    322: .Pp
                    323: A special capability,
                    324: .Ic tc= name ,
                    325: is used to indicate that the record specified by
                    326: .Fa name
                    327: should be substituted for the
                    328: .Ic tc
                    329: capability.
                    330: .Ic Tc
                    331: capabilities may interpolate records which also contain
                    332: .Ic tc
                    333: capabilities and more than one
                    334: .Ic tc
                    335: capability may be used in a record.  A
                    336: .Ic tc
                    337: expansion scope (i.e., where the argument is searched for) contains the
                    338: file in which the
                    339: .Ic tc
                    340: is declared and all subsequent files in the file array.
                    341: .Pp
                    342: When a database is searched for a capability record, the first matching
                    343: record in the search is returned.  When an record is scanned for a
                    344: capability, the first matching capability is returned; the capability
                    345: .Ic :nameT@:
                    346: will hide any following definition of a value of type
                    347: .Em T
                    348: for
                    349: .Fa name ;
                    350: and the capability
                    351: .Ic :name@:
                    352: will prevent any following values of
                    353: .Fa name
                    354: from being seen.
                    355: .Pp
                    356: These features combined with
                    357: .Ic tc
                    358: capabilities can be used to generate variations of other databases and
                    359: records by either adding new capabilities, overriding definitions with new
                    360: definitions, or hiding following definitions via `@' capabilities.
                    361: .Sh EXAMPLES
                    362: .Bd -unfilled -offset indent
                    363: example\||\|an example of binding multiple values to names:\e
                    364:        :foo%bar:foo^blah:foo@:\e
                    365:        :abc%xyz:abc^frap:abc$@:\e
                    366:        :tc=more:
                    367: .Ed
                    368: .Pp
                    369: The capability foo has two values bound to it (bar of type `%' and blah of
                    370: type `^') and any other value bindings are hidden.  The capability abc
                    371: also has two values bound but only a value of type `$' is prevented from
                    372: being defined in the capability record more.
                    373: .Pp
                    374: .Bd -unfilled -offset indent
                    375: file1:
                    376:        new\||\|new_record\||\|a modification of "old":\e
                    377:                :fript=bar:who-cares@:tc=old:blah:tc=extensions:
                    378: file2:
                    379:        old\||\|old_record\||\|an old database record:\e
                    380:                :fript=foo:who-cares:glork#200:
                    381: .Ed
                    382: .Pp
                    383: The records are extracted by calling
                    384: .Nm cgetent
                    385: with file1 preceding file2.
                    386: In the capability record new in file1, fript=bar overrides the definition
                    387: of fript=foo interpolated from the capability record old in file2,
                    388: who-cares@ prevents the definition of any who-cares definitions in old
                    389: from being seen, glork#200 is inherited from old, and blah and anything
                    390: defined by the record extensions is added to those definitions in old.
                    391: Note that the position of the fript=bar and who-cares@ definitions before
                    392: tc=old is important here.  If they were after, the definitions in old
                    393: would take precedence.
                    394: .Sh CGETNUM AND CGETSTR SYNTAX AND SEMANTICS
                    395: Two types are predefined by
                    396: .Nm cgetnum
                    397: and
                    398: .Nm cgetstr :
                    399: .Bl -column "nameXnumber"
                    400: .Sm off
                    401: .It Em name No \&# Em number Ta numeric
                    402: capability
                    403: .Em name
                    404: has value
                    405: .Em number
                    406: .It Em name No = Em string Ta "string capability"
                    407: .Em name
                    408: has value
                    409: .Em string
                    410: .It Em name No \&#@ Ta "the numeric capability"
                    411: .Em name
                    412: does not exist
                    413: .It Em name No \&=@ Ta "the string capability"
                    414: .Em name
                    415: does not exist
                    416: .El
                    417: .Pp
                    418: Numeric capability values may be given in one of three numeric bases.
                    419: If the number starts with either
                    420: .Ql 0x
                    421: or
                    422: .Ql 0X
                    423: it is interpreted as a hexadecimal number (both upper and lower case a-f
                    424: may be used to denote the extended hexadecimal digits).
                    425: Otherwise, if the number starts with a
                    426: .Ql 0
                    427: it is interpreted as an octal number.
                    428: Otherwise the number is interpreted as a decimal number.
                    429: .Pp
                    430: String capability values may contain any character.  Non-printable
                    431: .Dv ASCII
                    432: codes, new lines, and colons may be conveniently represented by the use
                    433: of escape sequences:
                    434: .Bl -column "\e\|X,X\e\|X" "(ASCII octal nnn)"
                    435: ^X     ('\fIX\fP' & 037)       control-\fIX\fP
                    436: \e\|b, \e\|B   (ASCII 010)     backspace
                    437: \e\|t, \e\|T   (ASCII 011)     tab
                    438: \e\|n, \e\|N   (ASCII 012)     line feed (newline)
                    439: \e\|f, \e\|F   (ASCII 014)     form feed
                    440: \e\|r, \e\|R   (ASCII 015)     carriage return
                    441: \e\|e, \e\|E   (ASCII 027)     escape
                    442: \e\|c, \e\|C   (:)     colon
                    443: \e\|\e (\e\|)  back slash
                    444: \e\|^  (^)     caret
                    445: \e\|\fInnn\fP  (ASCII octal \fInnn\fP)
                    446: .El
                    447: .Pp
                    448: A `\|\e' may be followed by up to three octal digits directly specifies
                    449: the numeric code for a character.  The use of
                    450: .Tn ASCII
                    451: .Dv NUL Ns s ,
                    452: while easily
                    453: encoded, causes all sorts of problems and must be used with care since
                    454: .Dv NUL Ns s
                    455: are typically used to denote the end of strings; many applications
                    456: use `\e\|200' to represent a
                    457: .Dv NUL .
                    458: .Sh DIAGNOSTICS
                    459: .Nm Cgetent ,
                    460: .Nm cgetset ,
                    461: .Nm cgetmatch ,
                    462: .Nm cgetnum ,
                    463: .Nm cgetstr ,
                    464: .Nm cgetustr ,
                    465: .Nm cgetfirst ,
                    466: and
                    467: .Nm cgetnext
                    468: return a a value greater than or equal to 0 on success and a value less
                    469: than 0 on failure.
                    470: .Nm Cgetcap
                    471: returns a character pointer on success and a
                    472: .Dv NULL
                    473: on failure.
                    474: .Pp
                    475: .Nm Cgetent ,
                    476: and
                    477: .Nm cgetseq
                    478: may fail and set
                    479: .Va errno
                    480: for any of the errors specified for the library functions:
                    481: .Xr fopen 2 ,
                    482: .Xr fclose 2 ,
                    483: .Xr open 2 ,
                    484: and
                    485: .Xr close 2 .
                    486: .Pp
                    487: .Nm Cgetent ,
                    488: .Nm cgetset ,
                    489: .Nm cgetstr ,
                    490: and
                    491: .Nm cgetustr
                    492: may fail and set
                    493: .Va errno
                    494: as follows:
                    495: .Bl -tag -width Er
                    496: .It Bq Er ENOMEM
                    497: No memory to allocate.
                    498: .El
                    499: .Sh SEE ALSO
                    500: .Xr cap_mkdb 1 ,
                    501: .Xr malloc 3
                    502: .Sh BUGS
                    503: Colons (`:') can't be used in names, types, or values.
                    504: .Pp
                    505: There are no checks for
                    506: .Ic tc= name
                    507: loops in
                    508: .Nm cgetent .
                    509: .Pp
                    510: The buffer added to the database by a call to
                    511: .Nm cgetset
                    512: is not unique to the database but is rather prepended to any database used.

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