When getting mount information for all filesystems, mount uses the
getfsstat(2) system call using the MNT_NOWAIT flag to indicate that
it wants to use the statfs information cached in the mount structure.
When the -v (verbose) flag is specified, we need to use the MNT_WAIT
flag to getfsstat(2) so that kernel will call VFS_STATFS to get the
current statfs statistics from each filesystem.

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