The -n option tells how many blocks to read from the block source.
The following example will read 3 blocks from zio-zero, channel 0

./zio-dump -n 3 /dev/zio/zzero-0000-0-0-*
Signed-off-by: Federico Vaga <federico.vaga@gmail.com>
Acked-by: Alessandro Rubini <rubini@gnudd.com>