ubi-tests: mkvol test: Checks return value 'ENOSPC' for 'ubi_mkvol'

ubi-tests: mkvol test: Checks return value 'ENOSPC' for 'ubi_mkvol'

UBI tests try to create too many volumes in mkvol_bad and mkvol_basic.
Currently mtd-utils allows return value 'ENFILE' from 'ubi_mkvol', that
works fine in most situations. But what if the number of PEBs equals to
the maximum count of volumes? For example, mkvol_basic test will fail in
a 64MiB flash with 512KiB PEB size.
Following is the output of mkvol_basic test:

  ======================================================================
  ======================================================================
  ======================================================================
  Test on mtdram, fastmap enabled, VID header offset factor 1
  ======================================================================
  ======================================================================
  ======================================================================
  mtdram: 64MiB, PEB size 512KiB, fastmap enabled
  Running mkvol_basic /dev/ubi0
  [mkvol_basic] mkvol_multiple():182: function ubi_mkvol() failed with
  error 28 (No space left on device)
  [mkvol_basic] mkvol_multiple():183: vol_id 122
  Error: mkvol_basic failed
  FAILURE

The reason is that there is no available PEB to support a new volume. We
can see following verbose in dmesg:

  ubi0: attached mtd0 (name "mtdram test device", size 64 MiB)
  ubi0: user volume: 0, internal volumes: 1, max. volumes count: 128
  ubi0: available PEBs: 122, total reserved PEBs: 6, PEBs reserved for
  bad PEB handling: 0

The maximum count of volumes is 128, so we can create 128 volumes
theoretically. But there are 122 available PEBs becauese of existence of
reserved PEBs. In addition, a volume occupies at least one PEB. Actually,
we can only create 122 volumes, Therefore, 'ubi_mkvol' returns 'ENOSPC'
when mkvol_basic tries to create 123rd volume. And we can see
corresponding error message in dmesg:

  ubi0 error: ubi_create_volume [ubi]: not enough PEBs, only 0 available
  ubi0 error: ubi_create_volume [ubi]: cannot create volume 122, error -28

So, 'ENOSPC' can happen before 'ENFILE' in flash with a small amount of
PEBs. This patch checks return value 'ENOSPC' for 'ubi_mkvol' when mkvol
test is trying to create too many volumes.

----------------------------------------

Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>
Signed-off-by: David Oberhollenzer <david.oberhollenzer@sigma-star.at>