CAP_FROM_TEXT(3)

NAME
cap_from_text, cap_to_text, cap_to_name, cap_from_name - capability state textual representation translation

SYNOPSIS
#include <sys/capability.h>

cap_t cap_from_text(const char *buf_p);
char *cap_to_text(cap_t caps, ssize_t *len_p);
int cap_from_name(const char *name, cap_value_t *cap_p);
char *cap_to_name(cap_value_t cap);

Link with -lcap.

DESCRIPTION
These functions translate a capability state between an internal representation and a textual one. The internal representation is managed by the capability functions in working storage. The textual representation is a structured, human-readable string suitable for display.

cap_from_text() allocates and initializes a capability state in working storage. It then sets the contents of this newly created capability state to the state represented by a human-readable, nul-terminated character string pointed to by buf_p. It returns a pointer to the newly created capability state. When the capability state in working storage is no longer required, the caller should free any releasable memory by calling cap_free() with cap_t as an argument. The function returns an error if it cannot parse the contents of the string pointed to by buf_p or does not recognize any capability_name or flag character as valid. The function also returns an error if any flag is both set and cleared within a single clause.

cap_to_text() converts the capability state in working storage identified by caps into a nul-terminated human-readable string. This function allocates any memory necessary to contain the string, and returns a pointer to the string. If the pointer len_p is not NULL, the function shall also return the full length of the string (not including the nul terminator) in the location pointed to by len_p. The capability state in working storage, identified by caps, is completely represented in the character string. When the capability state in working storage is no longer required, the caller should free any releasable memory by calling cap_free() with the returned string pointer as an argument.

cap_from_name() converts a text representation of a capability, such as "cap_chown", to its numerical representation (CAP_CHOWN=0), writing the decoded value into *cap_p. If cap_p is NULL no result is written, but the return code of the function indicates whether or not the specified capability can be represented by the library.

cap_to_name() converts a capability index value, cap, to a libcap-allocated textual string. This string should be deallocated with cap_free().

TEXTUAL REPRESENTATION
The text format is described in the cap_text_formats(7) man page.

RETURN VALUE
cap_from_text(), cap_to_text() and cap_to_name() return a non-NULL value on success, and NULL on failure. cap_from_name() returns 0 for success, and -1 on failure (unknown capability).

On failure, errno is set to EINVAL, or ENOMEM.

CONFORMING TO
cap_from_text() and cap_to_text() are specified by the withdrawn POSIX.1e draft specification. cap_from_name() and cap_to_name() are Linux extensions.

EXAMPLE
The example program below demonstrates the use of cap_from_text() and cap_to_text(). The following shell session shows some example runs:

$ ./a.out "cap_chown=p cap_chown+e"
caps_to_text() returned "cap_chown=ep"
$ ./a.out "all=pe cap_chown-e cap_kill-pe"
caps_to_text() returned "=ep cap_chown-e cap_kill-ep"

The source code of the program is as follows:

#include <stdlib.h>
#include <stdio.h>
#include <sys/capability.h>

#define handle_error(msg) \
    do { perror(msg); exit(EXIT_FAILURE); } while (0)

int
main(int argc, char *argv[])
{
    cap_t caps;
    char *txt_caps;

    if (argc != 2) {
        fprintf(stderr, "%s <textual-cap-set>\n", argv[0]);
        exit(EXIT_FAILURE);
    }

    caps = cap_from_text(argv[1]);
    if (caps == NULL)
        handle_error("cap_from_text");

    txt_caps = cap_to_text(caps, NULL);
    if (txt_caps == NULL)
        handle_error("cap_to_text");

    printf("caps_to_text() returned \"%s\"\n", txt_caps);

    if (cap_free(txt_caps) != 0 || cap_free(caps) != 0)
        handle_error("cap_free");

    exit(EXIT_SUCCESS);
}

SEE ALSO
libcap(3), cap_clear(3), cap_copy_ext(3), cap_get_file(3), cap_get_proc(3), cap_init(3), cap_text_formats(7), capabilities(7)