Re: parted is ALMOST suitable

[Reco <recoverym4n@gmail.com>]

	Hi.

On Mon, Nov 07, 2016 at 04:05:17PM +0100, tomas@tuxteam.de wrote:
> On Mon, Nov 07, 2016 at 09:35:32AM -0500, Greg Wooledge wrote:
> > I started writing that in my previous message, but then I actually
> > tested it on my own system.  Good thing I did, because I got the
> > same result as Richard: being in group disk, which has read/write
> > access on /dev/sda*, does NOT give you output in the FSTYPE and other
> > fields of lsblk -f.  It certainly surprised me.
> 
> Indeed. I suspect lsblk is checking the user ID itself instead of
> letting the OS do its thing. For whatever reasons I can't fathom.

According to the source (util-linux-2.25.2), '-f' flag should add these
to the output:

add_column(columns, ncolumns++, COL_NAME);
add_column(columns, ncolumns++, COL_FSTYPE);
add_column(columns, ncolumns++, COL_LABEL);
add_column(columns, ncolumns++, COL_UUID);
add_column(columns, ncolumns++, COL_TARGET);


To determine COL_FSTYPE, probe_device function is used.
The definition of this function contains this little gem (getuid call):

static void probe_device(struct blkdev_cxt *cxt)
{
...

    /* try udev DB */
    if (get_udev_properties(cxt) == 0)
        return;             /* success */

    cxt->probed = 1;

    /* try libblkid (fallback) */
    if (getuid() != 0)
        return;             /* no permissions to read from the device */

    pr = blkid_new_probe_from_filename(cxt->filename);
    if (!pr)
        return;

So whoever wrote this was either lazy or too smart or both, as
blkid_new_probe_from_filename does this:

blkid_probe blkid_new_probe_from_filename(const char *filename)
{
...

    fd = open(filename, O_RDONLY|O_CLOEXEC);
    if (fd < 0)
        return NULL;

I.e. insufficient device permissions will return NULL anyway, so there's
little point of checking whenever the calling user is root or not.

Reco