chsmack: using linux constants for Smack's names

It is better to rely on the centralisation of names in a
single file: it can avoid errors.

The declarations of <linux/xattr.h> contains the definitions
of the names of the Smack's security attributes.

As Smack only runs on Linux and libsmack doesn't provides
a centralized version of the names of the security attributes
(because it were not needed), using the linux header seems
to be a good choice.

Signed-off-by: José Bollo <jose.bollo@open.eurogiciel.org>
chsmack: put usage string at head

Setting it at head is a reading improvement for
developpers that can quickly show the usage of the
program. It also makes the main function more readable.

Signed-off-by: José Bollo <jose.bollo@open.eurogiciel.org>
chsmack: validation of labels

To prepare to the future of libsmack (that will include the
validation function 'smack_label_length'), the validation
of the smack labels is separated from the main function.

Signed-off-by: José Bollo <jose.bollo@open.eurogiciel.org>
chsmack: use of 'smack_new_label_from_path'

The library libsmack offer a function for reading
Smack labels. It is better to use the function of the
library.

Signed-off-by: José Bollo <jose.bollo@open.eurogiciel.org>
chsmack: use of 'smack_set_label_for_path'

To prepare to the future libsmack that will have a function
for writing Smack labels and to prepare to the handling of
symbolic links, the write of the labels is put in the
function 'smack_set_label_for_path'.

Signed-off-by: José Bollo <jose.bollo@open.eurogiciel.org>
chsmack: exchanging order of nested blocks if/for

Prepare to add the removing of labels and also reduce
the count of tests.

Signed-off-by: José Bollo <jose.bollo@open.eurogiciel.org>
chsmack: add dereference option

Add the options that allow to follow the symbolic
links instead of modifying it. There is no really
need but it may help.

The text of the short option is moved.
It prepares to scan options in two passes. It also
centralize the definition of options, avoiding to have
many lines between the definitions.

Signed-off-by: José Bollo <jose.bollo@open.eurogiciel.org>
chsmack: checking transmute on directories

The transmute flag is meaningfull only on directories.
The program now check that the transmute flag is set
only on directories.

Signed-off-by: José Bollo <jose.bollo@open.eurogiciel.org>
chsmack: using flags for labels

That modification prepare the addition of the option
to remove Smack labels. It seems also best to be agnostic
on what are valid smack labels (and rely on libsmack in the
futur) that maybe one day could be empty strings!

Signed-off-by: José Bollo <jose.bollo@open.eurogiciel.org>
chsmack: split option scan in two parts

It prepares the futur option to remove smack labels.
It also separate the validation of the labels what can
improve the readability of the code.

Also add a check that the option transmute isn't repeated.

Signed-off-by: José Bollo <jose.bollo@open.eurogiciel.org>
chsmack: add option to remove labels

Adding that option allow chsmack to remove the smack labels.
It is really important to have it.

Signed-off-by: José Bollo <jose.bollo@open.eurogiciel.org>
chsmack: refusing repeated labels

Refusing to set many time a label is important for
security. If a label is set more than one time, wich
label is to use? Wich is the good?

Signed-off-by: José Bollo <jose.bollo@open.eurogiciel.org>
chsmack: update of the manual

This new version of the manual includes the options
the dereferencing symbolic links and for removing
smack's labels.

Signed-off-by: José Bollo <jose.bollo@open.eurogiciel.org>