Skip site navigation (1)Skip section navigation (2)

FreeBSD Manual Pages

  
 
  

home | help
GETCAP(3)                 OpenBSD Programmer's Manual                GETCAP(3)

NAME
     cgetent, cgetset, cgetmatch, cgetcap, cgetnum, cgetstr, cgetustr,
     cgetfirst, cgetnext, cgetclose, cgetusedb - capability database access
     routines

SYNOPSIS
     #include <stdlib.h>

     int
     cgetent(char **buf, char **db_array, const char *name);

     int
     cgetset(const char *ent);

     int
     cgetmatch(char *buf, const char *name);

     char *
     cgetcap(char *buf, const char *cap, int type);

     int
     cgetnum(char *buf, const char *cap, long *num);

     int
     cgetstr(char *buf, const char *cap, char **str);

     int
     cgetustr(char *buf, const char *cap, char **str);

     int
     cgetfirst(char **buf, char **db_array);

     int
     cgetnext(char **buf, char **db_array);

     int
     cgetclose(void);

     int
     cgetusedb(int usedb);

DESCRIPTION
     The cgetent() function extracts the capability record name from the
     database specified by the null-terminated file array db_array and returns
     a pointer to a copy of it in buf. cgetent() will first look for files
     ending in ``.db'' (see cap_mkdb(1)) before accessing the ASCII version of
     the capability database.  buf must be retained through all subsequent
     calls to cgetmatch(), cgetcap(), cgetnum(), cgetstr(), and cgetustr(),
     but may then be free'd. On success 0 is returned, 1 if the returned
     record contains an unresolved tc expansion, -1 if the requested record
     couldn't be found, -2 if a system error occurred (couldn't open or read a
     file, for example) also setting errno, and -3 if a potential reference
     loop is detected (see tc= comments below).

     cgetset() enables the addition of a character buffer containing a single
     capability record entry to the capability database.  Conceptually, the
     entry is added as the first ``file'' in the database, and is therefore
     searched first on the call to cgetent().  The entry is passed in ent. If
     ent is NULL, the current entry is removed from the database.  cgetset()
     must precede the database traversal.  It must be called before cgetent().
     If a sequential access is being performed (see below), it must be called
     before the first sequential access call (cgetfirst() or cgetnext()), or
     be directly preceded by a cgetclose() call.  On success 0 is returned and
     -1 on failure.

     cgetmatch() will return 0 if name is one of the names of the capability
     record buf, -1 if not.

     cgetcap() searches the capability record buf for the capability cap with
     type type. A type is specified using any single character.  If a colon
     (`:') is used, an untyped capability will be searched for (see below for
     explanation of types).  A pointer to the value of cap in buf is returned
     on success or NULL if the requested capability couldn't be found.  The
     end of the capability value is signaled by a `:' or ASCII NUL (see below
     for capability database syntax).

     cgetnum() retrieves the value of the numeric capability cap from the ca-
     pability record pointed to by buf. The numeric value is returned in the
     long pointed to by num. On success 0 is returned, -1 if the requested nu-
     meric capability couldn't be found.

     cgetstr() retrieves the value of the string capability cap from the capa-
     bility record pointed to by buf. A pointer to a decoded, null-terminated,
     malloc'd copy of the string is returned in the char * pointed to by str.
     The number of characters in the decoded string (not including the trail-
     ing NUL) is returned on success, -1 if the requested string capability
     couldn't be found, or -2 if a system error was encountered (storage allo-
     cation failure).

     cgetustr() is identical to cgetstr() except that it does not expand spe-
     cial characters, but rather returns each character of the capability
     string literally.

     cgetfirst() and cgetnext() comprise a function group that provides for
     sequential access of the null-terminated array of file names, db_array.
     cgetfirst() returns the first record in the database and resets the ac-
     cess to the first record.  cgetnext() returns the next record in the
     database with respect to the record returned by the previous cgetfirst()
     or cgetnext() call.  If there is no such previous call, the first record
     in the database is returned.  Each record is returned in a malloc'd copy
     pointed to by buf. tc expansion is done (see tc= comments below).  Upon
     completion of the database 0 is returned, 1 is returned upon successful
     return of record with possibly more remaining (we haven't reached the end
     of the database yet), 2 is returned if the record contains an unresolved
     tc expansion, -1 is returned if an system error occurred, and -2 is re-
     turned if a potential reference loop is detected (see tc= comments be-
     low).  Upon completion of database (0 return) the database is closed.

     cgetclose() closes the sequential access and frees any memory and file
     descriptors being used.  Note that it does not erase the buffer pushed by
     a call to cgetset().

     cgetusedb() allows the user to specify whether use or ignore database
     files ending in ``.db''. If usedb is zero, files ending in ``.db'' will
     be ignored.  If usedb is non-zero, files ending in ``.db'' will be used
     in preference to the text version.  The default is to process ``.db''
     files.  cgetusedb() returns the previous setting.

   Capability database syntax
     Capability databases are normally ASCII and may be edited with standard
     text editors.  Blank lines and lines beginning with a `#' are comments
     and are ignored.  Lines ending with a `\' indicate that the next line is
     a continuation of the current line; the `\' and following newline are ig-
     nored.  Long lines are usually continued onto several physical lines by
     ending each line except the last with a `\'.

     Capability databases consist of a series of records, one per logical
     line.  Each record contains a variable number of colon-separated fields
     (capabilities).  Empty fields consisting entirely of whitespace charac-
     ters (spaces and tabs) are ignored.

     The first capability of each record specifies its names, separated by `|'
     characters.  These names are used to reference records in the database.
     By convention, the last name is usually a comment and is not intended as
     a lookup tag.  For example, the ``vt100'' record from the termcap
     database begins:

           d0|vt100|vt100-am|vt100am|dec vt100:

     giving four names that can be used to access the record.

     The remaining non-empty capabilities describe a set of (name, value)
     bindings, consisting of a names optionally followed by a typed values:

     name          typeless [boolean] capability name is present [true]
     nameTvalue    capability (name, T) has value value
     name@         no capability name exists
     nameT@        capability (name, T) does not exist

     Names consist of one or more characters.  Names may contain any character
     except `:', but it's usually best to restrict them to the printable char-
     acters and avoid use of graphics like `#', `=', `%', `@', etc.  Types are
     single characters used to separate capability names from their associated
     typed values.  Types may be any character except a `:'. Typically, graph-
     ics like `#', `=', `%', etc. are used.  Values may be any number of char-
     acters and may contain any character except `:'.

   Capability database semantics
     Capability records describe a set of (name, value) bindings.  Names may
     have multiple values bound to them.  Different values for a name are dis-
     tinguished by their types. cgetcap() will return a pointer to a value of
     a name given the capability name and the type of the value.

     The types `#' and `=' are conventionally used to denote numeric and
     string typed values, but no restriction on those types is enforced.  The
     functions cgetnum() and cgetstr() can be used to implement the tradition-
     al syntax and semantics of `#' and `='. Typeless capabilities are typi-
     cally used to denote boolean objects with presence or absence indicating
     truth and false values respectively.  This interpretation is conveniently
     represented by:

           (getcap(buf, name, ':') != NULL)

     A special capability, tc= name, is used to indicate that the record spec-
     ified by name should be substituted for the tc capability.  tc capabili-
     ties may interpolate records which also contain tc capabilities and more
     than one tc capability may be used in a record.  A tc expansion scope
     (i.e., where the argument is searched for) contains the file in which the
     tc is declared and all subsequent files in the file array.

     When a database is searched for a capability record, the first matching
     record in the search is returned.  When a record is scanned for a capa-
     bility, the first matching capability is returned; the capability
     :nameT@: will hide any following definition of a value of type T for
     name; and the capability :name@: will prevent any following values of
     name from being seen.

     These features combined with tc capabilities can be used to generate
     variations of other databases and records by either adding new capabili-
     ties, overriding definitions with new definitions, or hiding following
     definitions via `@' capabilities.

   cgetnum() and cgetstr() syntax and semantics
     Two types are predefined by cgetnum() and cgetstr():

     name#number    numeric capability name has value number
     name=string    string capability name has value string
     name#@         the numeric capability name does not exist
     name=@         the string capability name does not exist

     Numeric capability values may be given in one of three numeric bases.  If
     the number starts with either `0x' or `0X' it is interpreted as a hex-
     adecimal number (both upper and lower case a-f may be used to denote the
     extended hexadecimal digits).  Otherwise, if the number starts with a `0'
     it is interpreted as an octal number.  Otherwise the number is interpret-
     ed as a decimal number.

     String capability values may contain any character.  Non-printable ASCII
     codes, new lines, and colons may be conveniently represented by the use
     of escape sequences:

     ^X        ('X' & 037)          control-X
     \b, \B    (ASCII 010)          backspace
     \t, \T    (ASCII 011)          tab
     \n, \N    (ASCII 012)          line feed (newline)
     \f, \F    (ASCII 014)          form feed
     \r, \R    (ASCII 015)          carriage return
     \e, \E    (ASCII 027)          escape
     \c, \C    (:)                  colon
     \\        (\)                  back slash
     \^        (^)                  caret
     \nnn      (ASCII octal nnn)

     A `\' may be followed by up to three octal digits directly specifies the
     numeric code for a character.  The use of ASCII NULs, while easily encod-
     ed, causes all sorts of problems and must be used with care since NULs
     are typically used to denote the end of strings; many applications use
     `\200' to represent a NUL.

EXAMPLES
           example|an example of binding multiple values to names:\
                :foo%bar:foo^blah:foo@:\
                :abc%xyz:abc^frap:abc$@:\
                :tc=more:

     The capability foo has two values bound to it (bar of type `%' and blah
     of type `^') and any other value bindings are hidden.  The capability abc
     also has two values bound but only a value of type `$' is prevented from
     being defined in the capability record more.

           file1:
                new|new_record|a modification of "old":\
                     :fript=bar:who-cares@:tc=old:blah:tc=extensions:
           file2:
                old|old_record|an old database record:\
                     :fript=foo:who-cares:glork#200:

     The records are extracted by calling cgetent() with file1 preceding
     file2.  In the capability record new in file1, fript=bar overrides the
     definition of fript=foo interpolated from the capability record old in
     file2, who-cares@ prevents the definition of any who-cares definitions in
     old from being seen, glork#200 is inherited from old, and blah and any-
     thing defined by the record extensions is added to those definitions in
     old.  Note that the position of the fript=bar and who-cares@ definitions
     before tc=old is important here.  If they were after, the definitions in
     old would take precedence.

DIAGNOSTICS
     cgetent(), cgetset(), cgetmatch(), cgetnum(), cgetstr(), cgetustr(),
     cgetfirst(), and cgetnext() return a value greater than or equal to 0 on
     success and a value less than 0 on failure.  cgetcap() returns a charac-
     ter pointer on success and a NULL on failure.

     cgetent() and cgetset() may fail and set errno for any of the errors
     specified for the library functions fopen(3), fclose(3), open(2), and
     close(2).

     cgetent(), cgetset(), cgetstr(), and cgetustr() may fail and set errno as
     follows:

     [ENOMEM]      No memory to allocate.

SEE ALSO
     cap_mkdb(1), malloc(3)

BUGS
     Colon (`:') characters cannot be used in names, types, or values.

     There are no checks for tc=name loops in cgetent().

     The buffer added to the database by a call to cgetset() is not unique to
     the database but is rather prepended to any database used.

OpenBSD 3.1                     April 19, 1994                               5

NAME | SYNOPSIS | DESCRIPTION | EXAMPLES | DIAGNOSTICS | SEE ALSO | BUGS

Want to link to this manual page? Use this URL:
<https://www.freebsd.org/cgi/man.cgi?query=getcap&sektion=3&manpath=OpenBSD+3.1>

home | help