GETCAP(3) 386BSD Programmer's Manual GETCAP(3)
NAME
cgetent, cgetset, cgetmatch, cgetcap, cgetnum, cgetstr, cgetustr,
cgetfirst, cgetnext, cgetclose - capability database access routines
SYNOPSIS
#include <stdlib.h>
int
cgetent(char **buf, char **db_array, char *name)
int
cgetset(char *ent)
int
cgetmatch(char *buf, char *name)
char *
cgetcap(char *buf, char *cap, char type)
int
cgetnum(char *buf, char *cap, long *num)
int
cgetstr(char *buf, char *cap, char **str)
int
cgetustr(char *buf, char *cap, char **str)
int
cgetfirst(char **buf, char **db_array)
int
cgetnext(char **buf, char **db_array)
int
cgetclose(void)
DESCRIPTION
Cgetent() extracts the capability rec name from the database specified by
the NULL terminated file array db_array and returns a pointer to a
malloc'd copy of it in buf. Cgetent will first look for files ending in
.db (see cap_mkdb(1)) before accessing the ASCII file. 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 was encountered (couldn't open/read a file, etc.) 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 the cgetent
call. 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, 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
capability record pointed to by buf. The numeric value is returned in the
long pointed to by num. 0 is returned on success, -1 if the requested
numeric capability couldn't be found.
Cgetstr retrieves the value of the string capability cap from the
capability record pointed to by buf. A pointer to a decoded, NUL
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 trailing NUL is returned on success, -1 if the requested
string capability couldn't be found, -2 if a system error was encountered
(storage allocation failure).
Cgetustr is identical to cgetstr except that it does not expand special
characters, but rather returns each character of the capability string
literally.
Cgetfirst, cgetnext, comprise a function group that provides for
sequential access of the NULL pointer terminated array of file names,
db_array. Cgetfirst returns the first record in the database and resets
the access 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 occured, and -2 is
returned if a potential reference loop is detected (see tc= comments
below). 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.
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
ignored. 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 `:'-separated fields
(capabilities). Empty fields consisting entirely of white space
characters (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
characters 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, graphics like `#', `=', `%', etc. are used. Values may be any
number of characters 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
distinguished 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 traditional
syntax and semantics of `#' and `='. Typeless capabilities are typically
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
specified by name should be substituted for the tc capability. Tc
capabilities 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 an record is scanned for a
capability, 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
capabilities, overriding definitions with new definitions, or hiding
following definitions via `@' capabilities.
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 anything
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.
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
hexadecimal 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
interpreted 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
encoded, 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.
DIAGNOSTICS
Cgetent, cgetset, cgetmatch, cgetnum, cgetstr, cgetustr, cgetfirst, and
cgetnext return a a value greater than or equal to 0 on success and a
value less than 0 on failure. Cgetcap returns a character pointer on
success and a NULL on failure.
Cgetent, and cgetseq may fail and set errno for any of the errors
specified for the library functions: fopen(2), fclose(2), 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
Colons (`:') can't 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.
BSD Experimental August 11, 1992 5