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[minix3.git] / lib / libc / gen / cgetcap.3

.\"     $NetBSD: cgetcap.3,v 1.8 2012/04/22 10:13:52 wiz Exp $
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.\" This code is derived from software contributed to Berkeley by
.\" Casey Leedom of Lawrence Livermore National Laboratory.
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.\"     @(#)getcap.3    8.4 (Berkeley) 5/13/94
.\"
.Dd April 5, 2012
.Dt CGETCAP 3
.Os
.Sh NAME
.Nm cgetent ,
.Nm cgetset ,
.Nm cgetmatch ,
.Nm cgetcap ,
.Nm cgetnum ,
.Nm cgetstr ,
.Nm cgetustr ,
.Nm cgetfirst ,
.Nm cgetnext ,
.Nm cgetclose ,
.Nm cexpandtc
.Nd capability database access routines
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In stdlib.h
.Ft int
.Fn cgetent "char **buf" "const char * const *db_array" "const char *name"
.Ft int
.Fn cgetset "const char *ent"
.Ft int
.Fn cgetmatch "const char *buf" "const char *name"
.Ft char *
.Fn cgetcap "char *buf" "const char *cap" "int type"
.Ft int
.Fn cgetnum "char *buf" "const char *cap" "long *num"
.Ft int
.Fn cgetstr "char *buf" "const char *cap" "char **str"
.Ft int
.Fn cgetustr "char *buf" "const char *cap" "char **str"
.Ft int
.Fn cgetfirst "char **buf" "const char * const *db_array"
.Ft int
.Fn cgetnext "char **buf" "const char * const *db_array"
.Ft int
.Fn cgetclose "void"
.Ft void
.Fn csetexpandtc "int expandtc"
.Sh DESCRIPTION
.Fn cgetent
extracts the capability
.Fa name
from the database specified by the
.Dv NULL
terminated file array
.Fa db_array
and returns a pointer to a
.Xr malloc 3 Ap d
copy of it in
.Fa buf .
.Fn cgetent
will first look for files ending in
.Pa .db
(see
.Xr cap_mkdb 1 )
before accessing the
.Tn ASCII
file.
.Pp
.Fa buf
must be retained through all subsequent calls to
.Fn cgetmatch ,
.Fn cgetcap ,
.Fn cgetnum ,
.Fn cgetstr ,
and
.Fn cgetustr ,
but may then be
.Xr free 3 Ap d .
.Pp
On success 0 is returned, 1 if the returned record contains an unresolved
.Qq 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
.Va errno ,
and \-3 if a potential reference loop is detected (see
.Qq tc=name
comments below).
.Pp
.Fn 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
.Dq file
in the database, and
is therefore searched first on the call to
.Fn cgetent .
The entry is passed in
.Fa ent .
If
.Fa ent
is
.Dv NULL ,
the current entry is removed from the database.
.Pp
.Fn cgetset
must precede the database traversal.
It must be called before the
.Fn cgetent
call.
If a sequential access is being performed (see below), it must be called
before the first sequential access call
.Po
.Fn cgetfirst
or
.Fn cgetnext
.Pc ,
or be directly preceded by a
.Fn cgetclose
call.
On success 0 is returned and \-1 on failure.
.Pp
.Fn cgetmatch
will return 0 if
.Fa name
is one of the names of the capability record
.Fa buf ,
\-1 if not.
.Pp
.Fn cgetcap
searches the capability record
.Fa buf
for the capability
.Fa cap
with type
.Fa type .
A
.Fa type
is specified using any single character.
If a colon
.Pq Sq \&:
is used, an untyped capability will be searched
for (see below for explanation of types).
A pointer to the value of
.Fa cap
in
.Fa buf
is returned on success,
.Dv NULL
if the requested capability couldn't be found.
The end of the capability value is signaled by a
.Sq \&: .
See
.Xr capfile 5
for a description of the capability syntax.
.Pp
.Fn cgetnum
retrieves the value of the numeric capability
.Fa cap
from the capability record pointed to by
.Fa buf .
The numeric value is returned in the
.Ft long
pointed to by
.Fa num .
0 is returned on success,
\-1 if the requested numeric capability couldn't be found.
.Pp
.Fn cgetstr
retrieves the value of the string capability
.Fa cap
from the capability record pointed to by
.Fa buf .
A pointer to a decoded,
.Dv NUL
terminated,
.Xr malloc 3 Ap d
copy of the string is returned in the
.Ft char *
pointed to by
.Fa str .
The number of characters in the decoded string not including the trailing
.Dv 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).
.Pp
.Fn cgetustr
is identical to
.Fn cgetstr
except that it does not expand special characters, but rather returns each
character of the capability string literally.
.Pp
.Fn cgetfirst ,
.Fn cgetnext ,
comprise a function group that provides for sequential access of the
.Dv NULL
pointer terminated array of file names,
.Fa db_array .
.Fn cgetfirst
returns the first record in the database and resets the access
to the first record.
.Fn cgetnext
returns the next record in the database with respect to the
record returned by the previous
.Fn cgetfirst
or
.Fn cgetnext
call.
If there is no such previous call,
the first record in the database is returned.
Each record is returned in a
.Xr malloc 3 Ap d
copy pointed to by
.Fa buf .
.Qq tc
expansion is done (see
.Qq tc=name
comments below).
.Pp
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
.Qq tc
expansion, \-1 is returned if an system error occurred, and \-2
is returned if a potential reference loop is detected (see
.Qq tc=name
comments below).
Upon completion of database (0 return) the database is closed.
.Pp
.Fn 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
.Fn cgetset .
.Sh 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
.Fa types .
.Fn cgetcap
will return a pointer to a value of a name given the capability name and
the type of the value.
.Pp
The types
.Sq #
and
.Sq =
are conventionally used to denote numeric and
string typed values, but no restriction on those types is enforced.
The functions
.Fn cgetnum
and
.Fn cgetstr
can be used to implement the traditional syntax and semantics of
.Sq #
and
.Sq = .
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:
.Pp
.Dl "(getcap(buf, name, ':') != NULL)"
.Pp
A special capability,
.Qq tc=name ,
is used to indicate that the record specified by
.Fa name
should be substituted for the
.Qq tc
capability.
.Qq tc
capabilities may interpolate records which also contain
.Qq tc
capabilities and more than one
.Qq tc
capability may be used in a record.
A
.Qq tc
expansion scope (i.e. where the argument is searched for) contains the
file in which the
.Qq tc
is declared and all subsequent files in the file array.
.Pp
.Fn csetexpandtc
can be used to control if
.Qq tc
expansion is performed or not.
.Sh DIAGNOSTICS
.Fn cgetent ,
.Fn cgetset ,
.Fn cgetmatch ,
.Fn cgetnum ,
.Fn cgetstr ,
.Fn cgetustr ,
.Fn cgetfirst ,
and
.Fn cgetnext
return a value greater than or equal to 0 on success and a value less
than 0 on failure.
.Fn cgetcap
returns a character pointer on success and a
.Dv NULL
on failure.
.Pp
.Fn cgetclose ,
.Fn cgetent ,
.Fn cgetfirst ,
and
.Fn cgetnext
may fail and set
.Va errno
for any of the errors specified for the library functions:
.Xr fopen 3 ,
.Xr fclose 3 ,
.Xr open 2 ,
and
.Xr close 2 .
.Pp
.Fn cgetent ,
.Fn cgetset ,
.Fn cgetstr ,
and
.Fn cgetustr
may fail and set
.Va errno
as follows:
.Bl -tag -width Er
.It Bq Er ENOMEM
No memory to allocate.
.El
.Sh SEE ALSO
.Xr cap_mkdb 1 ,
.Xr malloc 3 ,
.Xr capfile 5
.Sh BUGS
There are no checks for
.Qq tc=name
loops in
.Fn cgetent .
.Pp
The buffer added to the database by a call to
.Fn cgetset
is not unique to the database but is rather prepended to any database used.