toollib: override the PV device with duplicates

toollib: override the PV device with duplicates

When multiple duplicate devices are specified on the
command line, the PV is processed once for each of them,
but pv->dev is the device used each time.

This overrides the PV device to reflect the duplicate
device that was specified on the command line.  This is
done by hacking the lvmcache to replace pv->dev with the
device of the duplicate being processed.  (It would be
preferable to override pv->dev without munging the content
of the cache, and without sprinkling special cases throughout
the code.)

This override only applies when multiple duplicate devices are
specified on the command line.  When only a single duplicate
device of pv->dev is specified, the priority is to display the
cached pv->dev, so pv->dev is not overridden by the named
duplicate device.

In the examples below, loop3 is the cached device referenced
by pv->dev, and is given priority for processing.  Only after
loop3 is processed/displayed, will other duplicate devices
loop0/loop1 appear (when requested on the command line.)

With two duplicate devices, loop0 and loop3:

  # pvs
  Found duplicate PV XhLbpVo0hmuwrMQLjfxuAvPFUFZqD4vr: using /dev/loop3 not /dev/loop0
  PV         VG           Fmt  Attr PSize   PFree
  /dev/loop3 loopa        lvm2 a--   12.00m  12.00m

  # pvs /dev/loop3
  Found duplicate PV XhLbpVo0hmuwrMQLjfxuAvPFUFZqD4vr: using /dev/loop3 not /dev/loop0
  PV         VG    Fmt  Attr PSize  PFree
  /dev/loop3 loopa lvm2 a--  12.00m 12.00m

  # pvs /dev/loop0
  Found duplicate PV XhLbpVo0hmuwrMQLjfxuAvPFUFZqD4vr: using /dev/loop3 not /dev/loop0
  PV         VG    Fmt  Attr PSize  PFree
  /dev/loop3 loopa lvm2 a--  12.00m 12.00m

  # pvs -o+dev_size /dev/loop0 /dev/loop3
  Found duplicate PV XhLbpVo0hmuwrMQLjfxuAvPFUFZqD4vr: using /dev/loop3 not /dev/loop0
  PV         VG    Fmt  Attr PSize  PFree  DevSize
  /dev/loop0 loopa lvm2 a--  12.00m 12.00m  16.00m
  /dev/loop3 loopa lvm2 a--  12.00m 12.00m  32.00m

With three duplicate devices, loop0, loop1, loop3:

  # pvs -o+dev_size
  Found duplicate PV XhLbpVo0hmuwrMQLjfxuAvPFUFZqD4vr: using /dev/loop1 not /dev/loop0
  Found duplicate PV XhLbpVo0hmuwrMQLjfxuAvPFUFZqD4vr: using /dev/loop3 not /dev/loop1
  PV         VG           Fmt  Attr PSize   PFree   DevSize
  /dev/loop3 loopa        lvm2 a--   12.00m  12.00m  32.00m

  # pvs -o+dev_size /dev/loop3
  Found duplicate PV XhLbpVo0hmuwrMQLjfxuAvPFUFZqD4vr: using /dev/loop1 not /dev/loop0
  Found duplicate PV XhLbpVo0hmuwrMQLjfxuAvPFUFZqD4vr: using /dev/loop3 not /dev/loop1
  PV         VG    Fmt  Attr PSize  PFree  DevSize
  /dev/loop3 loopa lvm2 a--  12.00m 12.00m  32.00m

  # pvs -o+dev_size /dev/loop0
  Found duplicate PV XhLbpVo0hmuwrMQLjfxuAvPFUFZqD4vr: using /dev/loop1 not /dev/loop0
  Found duplicate PV XhLbpVo0hmuwrMQLjfxuAvPFUFZqD4vr: using /dev/loop3 not /dev/loop1
  PV         VG    Fmt  Attr PSize  PFree  DevSize
  /dev/loop3 loopa lvm2 a--  12.00m 12.00m  32.00m

  # pvs -o+dev_size /dev/loop1
  Found duplicate PV XhLbpVo0hmuwrMQLjfxuAvPFUFZqD4vr: using /dev/loop1 not /dev/loop0
  Found duplicate PV XhLbpVo0hmuwrMQLjfxuAvPFUFZqD4vr: using /dev/loop3 not /dev/loop1
  PV         VG    Fmt  Attr PSize  PFree  DevSize
  /dev/loop3 loopa lvm2 a--  12.00m 12.00m  32.00m

  # pvs -o+dev_size /dev/loop3 /dev/loop0
  Found duplicate PV XhLbpVo0hmuwrMQLjfxuAvPFUFZqD4vr: using /dev/loop1 not /dev/loop0
  Found duplicate PV XhLbpVo0hmuwrMQLjfxuAvPFUFZqD4vr: using /dev/loop3 not /dev/loop1
  PV         VG    Fmt  Attr PSize  PFree  DevSize
  /dev/loop0 loopa lvm2 a--  12.00m 12.00m  16.00m
  /dev/loop3 loopa lvm2 a--  12.00m 12.00m  32.00m

  # pvs -o+dev_size /dev/loop3 /dev/loop1
  Found duplicate PV XhLbpVo0hmuwrMQLjfxuAvPFUFZqD4vr: using /dev/loop1 not /dev/loop0
  Found duplicate PV XhLbpVo0hmuwrMQLjfxuAvPFUFZqD4vr: using /dev/loop3 not /dev/loop1
  PV         VG    Fmt  Attr PSize  PFree  DevSize
  /dev/loop1 loopa lvm2 a--  12.00m 12.00m  32.00m
  /dev/loop3 loopa lvm2 a--  12.00m 12.00m  32.00m

  # pvs -o+dev_size /dev/loop0 /dev/loop1
  Found duplicate PV XhLbpVo0hmuwrMQLjfxuAvPFUFZqD4vr: using /dev/loop1 not /dev/loop0
  Found duplicate PV XhLbpVo0hmuwrMQLjfxuAvPFUFZqD4vr: using /dev/loop3 not /dev/loop1
  PV         VG    Fmt  Attr PSize  PFree  DevSize
  /dev/loop1 loopa lvm2 a--  12.00m 12.00m  32.00m
  /dev/loop3 loopa lvm2 a--  12.00m 12.00m  32.00m

  # pvs -o+dev_size /dev/loop0 /dev/loop1 /dev/loop3
  Found duplicate PV XhLbpVo0hmuwrMQLjfxuAvPFUFZqD4vr: using /dev/loop1 not /dev/loop0
  Found duplicate PV XhLbpVo0hmuwrMQLjfxuAvPFUFZqD4vr: using /dev/loop3 not /dev/loop1
  PV         VG    Fmt  Attr PSize  PFree  DevSize
  /dev/loop0 loopa lvm2 a--  12.00m 12.00m  16.00m
  /dev/loop1 loopa lvm2 a--  12.00m 12.00m  32.00m
  /dev/loop3 loopa lvm2 a--  12.00m 12.00m  32.00m