QStorageInfo/Linux: use FS_IOC_GETFSLABEL to get the labels

This ioctl was introduced in kernel version 4.18 and before that it was
used for btrfs alone. It is currently (kernel v6.7) supported by:
 * btrfs
 * ext2/ext4
 * f2fs
 * gfs2
 * xfs
See man ioctl_fslabel(2)

This means we won't need to list the /dev/disks/by-label directory if
you only have mounted filesystems like the above or tmpfs (which doesn't
support labels).

On my system, there are still two cases that cause the listing:
 * a mount point not readable by my user, such as /.snapshots and /root
 * a FAT32 filesystem mounted on /boot/efi

Pick-to: 6.7
Change-Id: I76ffba14ece04f24b43efffd17ab3dced74ffd2c
Reviewed-by: Ahmad Samir <a.samirh78@gmail.com>
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>

0 files changed, 0 insertions, 0 deletions