[$] listmount() and statmount()

Years ago, the list of mounted filesystems on a Unix or Linux machine was
relatively short and static. Adding a filesystem, which typically involved
buying a new drive, happened rarely. In contrast, contemporary systems
with a large number of containers can have a long and dynamic list of
mounted filesystems. As was discussed at
the 2023 LSFMM+BPF Summit, the Linux
kernel's mechanism for providing information about mounted filesystems has
not kept up with this change, leading to system-management headaches. Now,
two new system calls proposed
by Miklos Szeredi look set to provide some much-needed pain relief.