The mountinfo parser implemented via `fmt.Sscanf()` is slower than the one
using `strings.Split()` and `strconv.Atoi()`. This rewrite helps to speed it
up to a factor of 8x, here is a result from go bench:
> BenchmarkParsingScanf-4 300 22294112 ns/op
> BenchmarkParsingSplit-4 3000 2780703 ns/op
I tried other approaches, such as using `fmt.Sscanf()` for the first
three (integer) fields and `strings.Split()` for the rest, but it slows
things down considerably:
> BenchmarkParsingMixed-4 1000 8827058 ns/op
Note the old code uses `fmt.Sscanf`, when a linear search for '-' field,
when a split for the last 3 fields. The new code relies on a single
split.
I have also added more comments to aid in future development.
Finally, the test data is fixed to now have white space before the first field.
Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
c611f18a7f