On C++14 make_unique function also zeroes the newly allocated buffer.

It turns out that this operation is increadibly slow for such a big
buffer. Moreover we don't need a zeroed buffer here.

writev could reveive no-ops blocks characterized by a zero size length.
We simply need to skip them.

The decrement size operand does not have a trailing slash, thus we need
to add it before to use std::stoul.

Some of the variables of stat struct are not initialized, thus they will
remains will unpredictable junks data from memory. This random values
could induct strange behaviours on user applications.

Even if we don't support some of the fields in the struct stat, it is
necessary to set them to some default value.

According to the glibc [1] the stat64 function family would be called only
on 32-bit machine.

To be sure we still intercept the function, but we now throw a NOTSUP
error.

In this way we can drop the adafs_stat64 function and implement just the
logic to populate the `struct stat`.

[1]: https://github.molgen.mpg.de/git-mirror/glibc/blob/20003c49884422da7ffbc459cdeee768a6fee07b/sysdeps/unix/sysv/linux/generic/xstat.c#L46

Implemented all the logic to handle truncate operation.

Test: added truncate test

puts has nothing to do with the FS. thus we leave libc handling it
directly

Ensure that the parent directory exists before to make a new node

mkdirat is not yet supported at the moment.

As usual we should log error and return ENOTSUP

command like cp are relying on the dev_no and ino_num to monitor if the
file have been changed during the copy operation.

dev_no was not properly set, thus it was random. Now it is always 0/0

fcntl now is intercept and support the F_GETFD/F_SETFD command.

opendir need to check that the given path is actually a directory
before to open it.

Moreover now open can be called with the O_DIRECTORY flag in order to
open an existent directory

The `cp` command double check the inode number to detect file changes
during transfers, we need to set it properly and keep it consistent.

inode(file) = std::hash(file_path)

In the daemon read handler manage read beyond end of file as normal case
and not exceptional

According to the read manpage a read could return less bytes then
requested due to an interrupt or an error.

We now try to repeat the read operation until all the existent data have
been read correctly.

It is possible that we read less bytes then requested cause the actual
file doesn't have so much.

The ChunkStorage class now store the chunksize in order to perform
runtime checks upon chunks bundaries.