NAME

       aa_features - an opaque object representing a set of AppArmor kernel features

       aa_features_new - create a new aa_features object based on a path

       aa_features_new_from_string - create a new aa_features object based on a string

       aa_features_new_from_kernel - create a new aa_features object based on the current kernel

       aa_features_ref - increments the ref count of an aa_features object

       aa_features_unref - decrements the ref count and frees the aa_features object when 0

       aa_features_write_to_fd - write a string representation of an aa_features object to a file
       descriptor

       aa_features_write_to_file - write a string representation of an aa_features object to a
       file

       aa_features_is_equal - equality test for two aa_features objects

       aa_features_supports - provides aa_features object support status

       aa_features_id - provides unique identifier for an aa_features object

       aa_features_value - the value associated with a given feature.

SYNOPSIS

       #include <sys/apparmor.h>

       typedef struct aa_features aa_features;

       int aa_features_new(aa_features **features, int dirfd, const char *path);

       int aa_features_new_from_file(aa_features **features, int fd);

       int aa_features_new_from_string(aa_features **features, const char *string, size_t size);

       int aa_features_new_from_kernel(aa_features **features);

       aa_features *aa_features_ref(aa_features *features);

       void aa_features_unref(aa_features *features);

       int aa_features_write_to_fd(aa_features *features, int fd);

       int aa_features_write_to_file(aa_features *features, int dirfd, const char *path);

       bool aa_features_is_equal(aa_features *features1, aa_features *features2);

       bool aa_features_supports(aa_features *features, const char *str);

       char *aa_features_id(aa_features *features);

       char *aa_features_value(aa_features *features, const char *str, size_t *len);

       Link with -lapparmor when compiling.

DESCRIPTION

       The aa_features object contains information about the AppArmor features supported by a
       kernel. The feature support information is based upon the files AppArmor represents in
       securityfs, which is typically found at /sys/kernel/security/apparmor/features/. That
       information may be parsed and turned into a string or flat file in order to represent a
       set of features of a kernel that is not currently running.

       The aa_features_new() function creates an aa_features object based upon a directory file
       descriptor and path. The path can point to a file or directory. See the openat(2) man page
       for examples of dirfd and path. The allocated features object must be freed using
       aa_features_unref().

       The aa_features_new_from_file() function is similar except that it accepts an open file as
       the argument. The allocated features object must be freed using aa_features_unref().

       The aa_features_new_from_string() function is similar except that it accepts a NUL-
       terminated string representation of the AppArmor features as the string argument. The
       length of the features string, not counting the NUL-terminator, must be specified as the
       size argument. The allocated features object must be freed using aa_features_unref().

       The aa_features_new_from_kernel() function creates an aa_features object from the current
       running kernel. The allocated features object must be freed using aa_features_unref().

       aa_features_ref() increments the reference count on the features object.

       aa_features_unref() decrements the reference count on the features object and releases all
       corresponding resources when the reference count reaches zero.

       The aa_features_write_to_fd() function writes a string representation of the features
       object to the file descriptor specified by the fd.

       The aa_features_write_to_file() function writes a string representation of the features
       object to the file specified by the dirfd and path combination.

       aa_features_is_equal() can be used to detect if the features1 and features2 objects are
       equal. The definition of equality is private to libapparmor and may be changed in ways
       that do not break backward compatibility.

       The aa_features_supports() function can be used to query the features object to determine
       if a feature is supported. The str argument should be equal to the path, relative to the
       "apparmor/features/" directory of securityfs, of the feature to query. For example, to
       test if policy version 6 is supported, str would be "policy/versions/v6".

       The aa_features_id() function returns a string representation of an identifier that can be
       used to uniquely identify an aa_features object.  The mechanism for generating the string
       representation is internal to libapparmor and subject to change but an example
       implementation is applying a hash function to the features string.

RETURN VALUE

       The aa_features_new() family of functions return 0 on success and *features will point to
       an aa_features object that must be freed by aa_features_unref(). -1 is returned on error,
       with errno set appropriately, and *features will be set to NULL.

       aa_features_ref() returns the value of features.

       aa_features_write_to_file() returns 0 on success. -1 is returned on error, with errno set
       appropriately.

       aa_features_is_equal() returns true if features1 and features2 are equal and false if they
       are not equal.

       aa_features_supports() returns true if the feature represented by str is supported and
       false if it is not supported.

       aa_features_id() returns a string identifying features which must be freed by the caller.
       NULL is returned on error, with errno set appropriately.

       aa_features_value() returns a null terminated string with is associated length which must
       be freed by the caller. NULL is returned on error, with errno set to ENOENT if the feature
       was not found, ENODIR if the specified feature does not resolve to a leaf feature.

ERRORS

       The errno value will be set according to the underlying error in the aa_features family of
       functions that return -1 or NULL on error.

NOTES

       The aa_features_id() function can be found in libapparmor version 2.13. All the other
       aa_feature functions described above are present in libapparmor version 2.10.

       aa_features_unref() saves the value of errno when called and restores errno before exiting
       in libapparmor version 2.12 and newer.

BUGS

       None known. If you find any, please report them at
       <https://gitlab.com/apparmor/apparmor/-/issues>.

SEE ALSO

       openat(2), aa-features-abi(1) and <https://wiki.apparmor.net>.