gen/FreeBSD/getcap.3

   1 .\" Copyright (c) 1992, 1993
   2 .\"     The Regents of the University of California.  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
   9 .\" are met:
  10 .\" 1. Redistributions of source code must retain the above copyright
  11 .\"    notice, this list of conditions and the following disclaimer.
  12 .\" 2. Redistributions in binary form must reproduce the above copyright
  13 .\"    notice, this list of conditions and the following disclaimer in the
  14 .\"    documentation and/or other materials provided with the distribution.
  15 .\" 4. Neither the name of the University nor the names of its contributors
  16 .\"    may be used to endorse or promote products derived from this software
  17 .\"    without specific prior written permission.
  18 .\"
  19 .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  20 .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  21 .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  22 .\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  23 .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  24 .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  25 .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  26 .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  27 .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  28 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  29 .\" SUCH DAMAGE.
  30 .\"
  31 .\"     @(#)getcap.3    8.4 (Berkeley) 5/13/94
  32 .\" $FreeBSD: src/lib/libc/gen/getcap.3,v 1.30 2007/02/11 18:14:49 maxim Exp $
  33 .\"
  34 .Dd March 22, 2002
  35 .Dt GETCAP 3
  36 .Os
  37 .Sh NAME
  38 .Nm cgetent ,
  39 .Nm cgetset ,
  40 .Nm cgetmatch ,
  41 .Nm cgetcap ,
  42 .Nm cgetnum ,
  43 .Nm cgetstr ,
  44 .Nm cgetustr ,
  45 .Nm cgetfirst ,
  46 .Nm cgetnext ,
  47 .Nm cgetclose
  48 .Nd capability database access routines
  49 .Sh LIBRARY
  50 .Lb libc
  51 .Sh SYNOPSIS
  52 .In stdlib.h
  53 .Ft int
  54 .Fn cgetent "char **buf" "char **db_array" "const char *name"
  55 .Ft int
  56 .Fn cgetset "const char *ent"
  57 .Ft int
  58 .Fn cgetmatch "const char *buf" "const char *name"
  59 .Ft char *
  60 .Fn cgetcap "char *buf" "const char *cap" "int type"
  61 .Ft int
  62 .Fn cgetnum "char *buf" "const char *cap" "long *num"
  63 .Ft int
  64 .Fn cgetstr "char *buf" "const char *cap" "char **str"
  65 .Ft int
  66 .Fn cgetustr "char *buf" "const char *cap" "char **str"
  67 .Ft int
  68 .Fn cgetfirst "char **buf" "char **db_array"
  69 .Ft int
  70 .Fn cgetnext "char **buf" "char **db_array"
  71 .Ft int
  72 .Fn cgetclose "void"
  73 .Sh DESCRIPTION
  74 The
  75 .Fn cgetent
  76 function extracts the capability
  77 .Fa name
  78 from the database specified by the
  79 .Dv NULL
  80 terminated file array
  81 .Fa db_array
  82 and returns a pointer to a
  83 .Xr malloc 3 Ns \&'d
  84 copy of it in
  85 .Fa buf .
  86 The
  87 .Fn cgetent
  88 function will first look for files ending in
  89 .Pa .db
  90 (see
  91 .Xr cap_mkdb 1 )
  92 before accessing the ASCII file.
  93 The
  94 .Fa buf
  95 argument
  96 must be retained through all subsequent calls to
  97 .Fn cgetmatch ,
  98 .Fn cgetcap ,
  99 .Fn cgetnum ,
 100 .Fn cgetstr ,
 101 and
 102 .Fn cgetustr ,
 103 but may then be
 104 .Xr free 3 Ns \&'d .
 105 On success 0 is returned, 1 if the returned
 106 record contains an unresolved
 107 .Ic tc
 108 expansion,
 109 \-1 if the requested record could not be found,
 110 \-2 if a system error was encountered (could not open/read a file, etc.) also
 111 setting
 112 .Va errno ,
 113 and \-3 if a potential reference loop is detected (see
 114 .Ic tc=
 115 comments below).
 116 .Pp
 117 The
 118 .Fn cgetset
 119 function enables the addition of a character buffer containing a single capability
 120 record entry
 121 to the capability database.
 122 Conceptually, the entry is added as the first ``file'' in the database, and
 123 is therefore searched first on the call to
 124 .Fn cgetent .
 125 The entry is passed in
 126 .Fa ent .
 127 If
 128 .Fa ent
 129 is
 130 .Dv NULL ,
 131 the current entry is removed from the database.
 132 A call to
 133 .Fn cgetset
 134 must precede the database traversal.
 135 It must be called before the
 136 .Fn cgetent
 137 call.
 138 If a sequential access is being performed (see below), it must be called
 139 before the first sequential access call
 140 .Fn ( cgetfirst
 141 or
 142 .Fn cgetnext ) ,
 143 or be directly preceded by a
 144 .Fn cgetclose
 145 call.
 146 On success 0 is returned and \-1 on failure.
 147 .Pp
 148 The
 149 .Fn cgetmatch
 150 function will return 0 if
 151 .Fa name
 152 is one of the names of the capability record
 153 .Fa buf ,
 154 \-1 if
 155 not.
 156 .Pp
 157 The
 158 .Fn cgetcap
 159 function searches the capability record
 160 .Fa buf
 161 for the capability
 162 .Fa cap
 163 with type
 164 .Fa type .
 165 A
 166 .Fa type
 167 is specified using any single character.
 168 If a colon (`:') is used, an
 169 untyped capability will be searched for (see below for explanation of
 170 types).
 171 A pointer to the value of
 172 .Fa cap
 173 in
 174 .Fa buf
 175 is returned on success,
 176 .Dv NULL
 177 if the requested capability could not be
 178 found.
 179 The end of the capability value is signaled by a `:' or
 180 .Tn ASCII
 181 .Dv NUL
 182 (see below for capability database syntax).
 183 .Pp
 184 The
 185 .Fn cgetnum
 186 function retrieves the value of the numeric capability
 187 .Fa cap
 188 from the capability record pointed to by
 189 .Fa buf .
 190 The numeric value is returned in the
 191 .Ft long
 192 pointed to by
 193 .Fa num .
 194 0 is returned on success, \-1 if the requested numeric capability could not
 195 be found.
 196 .Pp
 197 The
 198 .Fn cgetstr
 199 function retrieves the value of the string capability
 200 .Fa cap
 201 from the capability record pointed to by
 202 .Fa buf .
 203 A pointer to a decoded,
 204 .Dv NUL
 205 terminated,
 206 .Xr malloc 3 Ns \&'d
 207 copy of the string is returned in the
 208 .Ft char *
 209 pointed to by
 210 .Fa str .
 211 The number of characters in the decoded string not including the trailing
 212 .Dv NUL
 213 is returned on success, \-1 if the requested string capability could not
 214 be found, \-2 if a system error was encountered (storage allocation
 215 failure).
 216 .Pp
 217 The
 218 .Fn cgetustr
 219 function is identical to
 220 .Fn cgetstr
 221 except that it does not expand special characters, but rather returns each
 222 character of the capability string literally.
 223 .Pp
 224 The
 225 .Fn cgetfirst
 226 and
 227 .Fn cgetnext
 228 functions comprise a function group that provides for sequential
 229 access of the
 230 .Dv NULL
 231 pointer terminated array of file names,
 232 .Fa db_array .
 233 The
 234 .Fn cgetfirst
 235 function returns the first record in the database and resets the access
 236 to the first record.
 237 The
 238 .Fn cgetnext
 239 function returns the next record in the database with respect to the
 240 record returned by the previous
 241 .Fn cgetfirst
 242 or
 243 .Fn cgetnext
 244 call.
 245 If there is no such previous call, the first record in the database is
 246 returned.
 247 Each record is returned in a
 248 .Xr malloc 3 Ns \&'d
 249 copy pointed to by
 250 .Fa buf .
 251 .Ic Tc
 252 expansion is done (see
 253 .Ic tc=
 254 comments below).
 255 Upon completion of the database 0 is returned, 1 is returned upon successful
 256 return of record with possibly more remaining (we have not reached the end of
 257 the database yet), 2 is returned if the record contains an unresolved
 258 .Ic tc
 259 expansion, \-1 is returned if a system error occurred, and \-2
 260 is returned if a potential reference loop is detected (see
 261 .Ic tc=
 262 comments below).
 263 Upon completion of database (0 return) the database is closed.
 264 .Pp
 265 The
 266 .Fn cgetclose
 267 function closes the sequential access and frees any memory and file descriptors
 268 being used.
 269 Note that it does not erase the buffer pushed by a call to
 270 .Fn cgetset .
 271 .Sh CAPABILITY DATABASE SYNTAX
 272 Capability databases are normally
 273 .Tn ASCII
 274 and may be edited with standard
 275 text editors.
 276 Blank lines and lines beginning with a `#' are comments
 277 and are ignored.
 278 Lines ending with a `\|\e' indicate that the next line
 279 is a continuation of the current line; the `\|\e' and following newline
 280 are ignored.
 281 Long lines are usually continued onto several physical
 282 lines by ending each line except the last with a `\|\e'.
 283 .Pp
 284 Capability databases consist of a series of records, one per logical
 285 line.
 286 Each record contains a variable number of `:'-separated fields
 287 (capabilities).
 288 Empty fields consisting entirely of white space
 289 characters (spaces and tabs) are ignored.
 290 .Pp
 291 The first capability of each record specifies its names, separated by `|'
 292 characters.
 293 These names are used to reference records in the database.
 294 By convention, the last name is usually a comment and is not intended as
 295 a lookup tag.
 296 For example, the
 297 .Em vt100
 298 record from the
 299 .Xr termcap 5
 300 database begins:
 301 .Pp
 302 .Dl "d0\||\|vt100\||\|vt100-am\||\|vt100am\||\|dec vt100:"
 303 .Pp
 304 giving four names that can be used to access the record.
 305 .Pp
 306 The remaining non-empty capabilities describe a set of (name, value)
 307 bindings, consisting of a names optionally followed by a typed value:
 308 .Bl -column "nameTvalue"
 309 .It name Ta "typeless [boolean] capability"
 310 .Em name No "is present [true]"
 311 .It name Ns Em \&T Ns value Ta capability
 312 .Pq Em name , \&T
 313 has value
 314 .Em value
 315 .It name@ Ta "no capability" Em name No exists
 316 .It name Ns Em T Ns \&@ Ta capability
 317 .Pq Em name , T
 318 does not exist
 319 .El
 320 .Pp
 321 Names consist of one or more characters.
 322 Names may contain any character
 323 except `:', but it is usually best to restrict them to the printable
 324 characters and avoid use of graphics like `#', `=', `%', `@', etc.
 325 Types
 326 are single characters used to separate capability names from their
 327 associated typed values.
 328 Types may be any character except a `:'.
 329 Typically, graphics like `#', `=', `%', etc.\& are used.
 330 Values may be any
 331 number of characters and may contain any character except `:'.
 332 .Sh CAPABILITY DATABASE SEMANTICS
 333 Capability records describe a set of (name, value) bindings.
 334 Names may
 335 have multiple values bound to them.
 336 Different values for a name are
 337 distinguished by their
 338 .Fa types .
 339 The
 340 .Fn cgetcap
 341 function will return a pointer to a value of a name given the capability
 342 name and the type of the value.
 343 .Pp
 344 The types `#' and `=' are conventionally used to denote numeric and
 345 string typed values, but no restriction on those types is enforced.
 346 The
 347 functions
 348 .Fn cgetnum
 349 and
 350 .Fn cgetstr
 351 can be used to implement the traditional syntax and semantics of `#'
 352 and `='.
 353 Typeless capabilities are typically used to denote boolean objects with
 354 presence or absence indicating truth and false values respectively.
 355 This interpretation is conveniently represented by:
 356 .Pp
 357 .Dl "(getcap(buf, name, ':') != NULL)"
 358 .Pp
 359 A special capability,
 360 .Ic tc= name ,
 361 is used to indicate that the record specified by
 362 .Fa name
 363 should be substituted for the
 364 .Ic tc
 365 capability.
 366 .Ic Tc
 367 capabilities may interpolate records which also contain
 368 .Ic tc
 369 capabilities and more than one
 370 .Ic tc
 371 capability may be used in a record.
 372 A
 373 .Ic tc
 374 expansion scope (i.e., where the argument is searched for) contains the
 375 file in which the
 376 .Ic tc
 377 is declared and all subsequent files in the file array.
 378 .Pp
 379 When a database is searched for a capability record, the first matching
 380 record in the search is returned.
 381 When a record is scanned for a
 382 capability, the first matching capability is returned; the capability
 383 .Ic :nameT@:
 384 will hide any following definition of a value of type
 385 .Em T
 386 for
 387 .Fa name ;
 388 and the capability
 389 .Ic :name@:
 390 will prevent any following values of
 391 .Fa name
 392 from being seen.
 393 .Pp
 394 These features combined with
 395 .Ic tc
 396 capabilities can be used to generate variations of other databases and
 397 records by either adding new capabilities, overriding definitions with new
 398 definitions, or hiding following definitions via `@' capabilities.
 399 .Sh EXAMPLES
 400 .Bd -unfilled -offset indent
 401 example\||\|an example of binding multiple values to names:\e
 402         :foo%bar:foo^blah:foo@:\e
 403         :abc%xyz:abc^frap:abc$@:\e
 404         :tc=more:
 405 .Ed
 406 .Pp
 407 The capability foo has two values bound to it (bar of type `%' and blah of
 408 type `^') and any other value bindings are hidden.
 409 The capability abc
 410 also has two values bound but only a value of type `$' is prevented from
 411 being defined in the capability record more.
 412 .Pp
 413 .Bd -unfilled -offset indent
 414 file1:
 415         new\||\|new_record\||\|a modification of "old":\e
 416                 :fript=bar:who-cares@:tc=old:blah:tc=extensions:
 417 file2:
 418         old\||\|old_record\||\|an old database record:\e
 419                 :fript=foo:who-cares:glork#200:
 420 .Ed
 421 .Pp
 422 The records are extracted by calling
 423 .Fn cgetent
 424 with file1 preceding file2.
 425 In the capability record new in file1, fript=bar overrides the definition
 426 of fript=foo interpolated from the capability record old in file2,
 427 who-cares@ prevents the definition of any who-cares definitions in old
 428 from being seen, glork#200 is inherited from old, and blah and anything
 429 defined by the record extensions is added to those definitions in old.
 430 Note that the position of the fript=bar and who-cares@ definitions before
 431 tc=old is important here.
 432 If they were after, the definitions in old
 433 would take precedence.
 434 .Sh CGETNUM AND CGETSTR SYNTAX AND SEMANTICS
 435 Two types are predefined by
 436 .Fn cgetnum
 437 and
 438 .Fn cgetstr :
 439 .Bl -column "nameXnumber"
 440 .Sm off
 441 .It Em name No \&# Em number Ta numeric
 442 .Sm on
 443 capability
 444 .Em name
 445 has value
 446 .Em number
 447 .Sm off
 448 .It Em name No = Em string Ta "string capability"
 449 .Sm on
 450 .Em name
 451 has value
 452 .Em string
 453 .Sm off
 454 .It Em name No \&#@ Ta "the numeric capability"
 455 .Sm on
 456 .Em name
 457 does not exist
 458 .Sm off
 459 .It Em name No \&=@ Ta "the string capability"
 460 .Sm on
 461 .Em name
 462 does not exist
 463 .El
 464 .Pp
 465 Numeric capability values may be given in one of three numeric bases.
 466 If the number starts with either
 467 .Ql 0x
 468 or
 469 .Ql 0X
 470 it is interpreted as a hexadecimal number (both upper and lower case a-f
 471 may be used to denote the extended hexadecimal digits).
 472 Otherwise, if the number starts with a
 473 .Ql 0
 474 it is interpreted as an octal number.
 475 Otherwise the number is interpreted as a decimal number.
 476 .Pp
 477 String capability values may contain any character.
 478 Non-printable
 479 .Dv ASCII
 480 codes, new lines, and colons may be conveniently represented by the use
 481 of escape sequences:
 482 .Bl -column "\e\|X,X\e\|X" "(ASCII octal nnn)"
 483 ^X      ('X' & 037)     control-X
 484 \e\|b, \e\|B    (ASCII 010)     backspace
 485 \e\|t, \e\|T    (ASCII 011)     tab
 486 \e\|n, \e\|N    (ASCII 012)     line feed (newline)
 487 \e\|f, \e\|F    (ASCII 014)     form feed
 488 \e\|r, \e\|R    (ASCII 015)     carriage return
 489 \e\|e, \e\|E    (ASCII 027)     escape
 490 \e\|c, \e\|C    (:)     colon
 491 \e\|\e  (\e\|)  back slash
 492 \e\|^   (^)     caret
 493 \e\|nnn (ASCII octal nnn)
 494 .El
 495 .Pp
 496 A `\|\e' may be followed by up to three octal digits directly specifies
 497 the numeric code for a character.
 498 The use of
 499 .Tn ASCII
 500 .Dv NUL Ns s ,
 501 while easily
 502 encoded, causes all sorts of problems and must be used with care since
 503 .Dv NUL Ns s
 504 are typically used to denote the end of strings; many applications
 505 use `\e\|200' to represent a
 506 .Dv NUL .
 507 .Sh DIAGNOSTICS
 508 The
 509 .Fn cgetent ,
 510 .Fn cgetset ,
 511 .Fn cgetmatch ,
 512 .Fn cgetnum ,
 513 .Fn cgetstr ,
 514 .Fn cgetustr ,
 515 .Fn cgetfirst ,
 516 and
 517 .Fn cgetnext
 518 functions
 519 return a value greater than or equal to 0 on success and a value less
 520 than 0 on failure.
 521 The
 522 .Fn cgetcap
 523 function returns a character pointer on success and a
 524 .Dv NULL
 525 on failure.
 526 .Pp
 527 The
 528 .Fn cgetent ,
 529 and
 530 .Fn cgetset
 531 functions may fail and set
 532 .Va errno
 533 for any of the errors specified for the library functions:
 534 .Xr fopen 3 ,
 535 .Xr fclose 3 ,
 536 .Xr open 2 ,
 537 and
 538 .Xr close 2 .
 539 .Pp
 540 The
 541 .Fn cgetent ,
 542 .Fn cgetset ,
 543 .Fn cgetstr ,
 544 and
 545 .Fn cgetustr
 546 functions
 547 may fail and set
 548 .Va errno
 549 as follows:
 550 .Bl -tag -width Er
 551 .It Bq Er ENOMEM
 552 No memory to allocate.
 553 .El
 554 .Sh SEE ALSO
 555 .Xr cap_mkdb 1 ,
 556 .Xr malloc 3
 557 .Sh BUGS
 558 Colons (`:') cannot be used in names, types, or values.
 559 .Pp
 560 There are no checks for
 561 .Ic tc Ns = Ns Ic name
 562 loops in
 563 .Fn cgetent .
 564 .Pp
 565 The buffer added to the database by a call to
 566 .Fn cgetset
 567 is not unique to the database but is rather prepended to any database used.