mkfs: validate all input values

mkfs: validate all input values

Right now, mkfs does a poor job of input validation of values. Many
parameters do not check for trailing garbage and so will pass
obviously invalid values as OK. Some don't even detect completely
invalid values, leaving it for other checks later on to fail due to
a bad value conversion - these tend to rely on atoi() implicitly
returning a sane value when it is passed garbage, and atoi gives no
guarantee of the return value when passed garbage.

Clean all this up by passing all strings that need to be converted
into values into a common function that is called regardless of
whether unit conversion is needed or not. Further, make sure every
conversion is checked for a valid result, and abort the moment an
invalid value is detected.

Get rid of the silly "isdigits(), cvtnum()" calls which don't use
any of the conversion capabilities of cvtnum() because we've already
ensured that there are no conversion units in the string via the
isdigits() call. These can simply be replaced by a standard
strtoll() call followed by checking for no trailing bytes.

Finally, the block size of the filesystem is not known until all
the options have been parsed and we can determine if the default is
to be used. This means any parameter that relies on using conversion
from filesystem block size (the "NNNb" format) requires the block
size to first be specified on the command line so it is known.

Similarly, we make the same rule for specifying counts in sectors.
This is a change from the existing behaviour that assumes sectors
are 512 bytes unless otherwise changed on the command line. This,
unfortunately, leads to complete silliness where you can specify the
sector size as a count of sectors. It also means that you can do
some conversions with 512 byte sector sizes, and others with
whatever was specified on the command line, meaning the mkfs
behaviour changes depending in where in the command line the sector
size is changed....

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Jan Tulak <jtulak@redhat.com>
Reviewed-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>