Thanks to references from Brad Smith, BSDs use getmntinfo as
a system call for mounted filesystems.
Most BSDs return statfs structures, (and we use OSX's statfs64),
but NetBSD uses a statvfs structure.
Simplify Linux getmntent_r to just use getmntent.
AIX uses getmntent.
An attempt at writing Solaris compatibility with
a small bit of HPUX compatibility was made based on man page
entries only. Fixes welcome.
statvfs structures now use f_bsize for consistency with statfs
Test case adjusted as PATH_MAX is OS defined (e.g. 1023 on AIX)
Fixes: 0ee5cf837e
also fixes:
MDEV-27818: Disk plugin does not show zpool mounted devices
This is because zpool mounted point don't begin with /.
Due to the proliferation of multiple filesystem types since this
was written, we restrict the entries listed in the disks plugin
to excude:
* read only mount points (no point monitoring, and
includes squash, snaps, sysfs, procfs, cgroups...)
* mount points that aren't directories (excludes /etc/hostname and
similar mounts in containers). (getmntent (Linux/AIX) only)
* exclude systems where there is no capacity listed (excludes various
virtual filesystem types).
Reviewer: Sergei Golubchik
