1CAP_FROM_TEXT(3) Linux Programmer's Manual CAP_FROM_TEXT(3)
2
6 cap_from_text, cap_to_text, _cap_names - capability state textual rep‐
7 resentation translation
8
10 #include <sys/capability.h>
11 cap_t cap_from_text(const char *buf_p);
13 char *cap_to_text(cap_t caps, ssize_t *length_p);
15 extern char const *_cap_names[];
17
19 cc ... -lcap
20
22 These functions translate a capability state from an internal represen‐
23 tation into a textual one. The internal representation is managed by
24 the capability functions in working storage. The textual representation
25 is a structured, human-readable, string suitable for display.
26 cap_from_text allocates and initializes a capability state in working
28 storage. It then sets the contents of this newly-created capability
29 state to the state represented by human-readable, null terminated char‐
30 acter string pointed to by buf_p. It returns a pointer to the newly
31 created capability state. The caller should free any releasable mem‐
32 ory, when the capability state in working storage is no longer
33 required, by calling cap_free with cap_t as an argument. The function
34 returns an error if it cannot parse the contents of the string pointed
35 to by buf_p or does not recognize any capability_name or flag character
36 as valid. The function also returns an error if any flag is both set
37 and cleared within a single clause.
38 cap_to_text converts the capability state in working storage identified
40 by cap_p into a null terminated human-readable string. This function
41 allocates any memory necessary to contain the string, and returns a
42 pointer to the string. If the pointer len_p is not NULL, the function
43 shall also return the full length of the string (not including the null
44 terminator) in the location pointed to by len_p. The capability state
45 in working storage, identified by cap_p, is completely represented in
46 the character string. The caller should free any releasable memory,
47 when the capability state in working storage is no longer required, by
48 calling cap_free with cap_p as an argument.
49 _cap_names is an array of textual names for capability numbers.
51 Unnamed capabilities have a NULL entry. (This array is not defined by
52 POSIX.1e.)
53
55 A textual representation of capability sets consists of one or more
56 whitespace-separated clauses. Each clause specifies some operations to
57 a capability set; the set starts out with all capabilities lowered, and
58 the meaning of the string is the state of the capability set after all
59 the clauses have been applied in order.
60 Each clause consists of a list of comma-separated capability names (or
62 the word `all'), followed by an action-list. An action-list consists
63 of a sequence of operator flag pairs. Legal operators are: `=', '+',
64 and `-'. Legal flags are: `e', `i', and `p'. These flags are case-
65 sensitive and specify the Effective, Inheritable and Permitted sets
66 respectively.
67 In the capability name lists, all names are case-insensitive. The spe‐
69 cial name `all' specifies all capabilities; it is equivalent to a list
70 naming every capability individually.
71 Although not defined by POSIX, unnamed capabilities can be specified by
73 number.
74 The `=' operator indicates that the listed capabilities are first reset
76 in all three capability sets. The subsequent flags (which are optional
77 when associated with this operator) indicate that the listed capabili‐
78 ties for the corresponding set are to be raised. For example: "all=p"
79 means lower every capability in the Effective and Inheritable sets but
80 raise all of the Permitted capabilities; or, "cap_fowner=ep" means
81 raise the Effective and Permitted override-file-ownership capability,
82 while lowering this Inheritable capability.
83 In the case that the leading operator is `=', and no list of capabili‐
85 ties is provided, the action-list is assumed to refer to `all' capabil‐
86 ities. For example, the following three clauses are equivalent to each
87 other (and indicate a completely empty capability set): "all="; "=";
88 "cap_chown,<every-other-capability>=".
89 The operators, `+' and `-' both require an explicit preceding capabil‐
91 ity list and one or more explicit trailing flags. The `+' operator
92 will raise all of the listed capabilities in the flagged capability
93 sets. The `-' operator will lower all of the listed capabilities in
94 the flagged capability sets. For example: "all+p" will raise all of
95 the Permitted capabilities; "cap_fowner+p-i" will raise the override-
96 file-ownership capability in the Permitted capability set and lower
97 this Inheritable capability; "cap_fowner+pe-i" and "cap_fowner=+pe" are
98 equivalent.
99
101 cap_from_text and cap_to_text return a non-NULL value on success, and
102 NULL on failure.
103 On failure, errno(3) is set to EINVAL, or ENOMEM.
105
107 cap_from_text and cap_to_text are specified by POSIX.1e. _cap_names is
108 a Linux extension.
109
111 cap_clear(3), cap_copy_ext(3), cap_get_file(3), cap_get_proc(3),
112 cap_init(3)
113 26th May 1997 CAP_FROM_TEXT(3)