[Linux-NTFS-Dev] Portability of NTFS userspace code

[Richard R. <nt...@fl...>]

Hi all,

I've just committed a few changes to the ntfsprogs.

I've added compat.[ch] to hide a host of minor tweaks that will be
needed to get things to compile on Windows.  This is enough to get
around most of the GCCisms of the code, e.g. __attribute__.

One thing I've had to change is the reliance on void * arithmetic.
I was quite alarmed when I realised that gcc allows:

  void *v = "abc";
  v++;

It seems that they've decided to define sizeof (void) == 1.  Sensible,
but I don't think it's a standard.  At the moment, I've just cast the
pointers to (u8*).  A warning for this can be turned on using
-Wpointer-arith

We also seem to be relying on the size of __packed__ enums.  It's a
nice feature, but it's another gcc extension.  In our code we can:

  typedef enum {
    ABC = 4,
  } RICH __attribute__ ((__packed__));

The size of the type for the enum will be minimised, in this case to
1 byte.  Then we can use it in a struct, e.g.:

  struct x {
    int a;
    RICH r;
    int b;
  };

We rely on the enum being just one byte, but that's not portable.
One solution is to create and use the enumeration, but create a
strictly sized type for the struct, e.g.

  enum rich {
    ABC = 4,
  };
  typedef u8	RICH;

  struct x {
    int a;
    RICH r;
    int b;
  };

The next problem is the casting of parameters for Dprintf.  At the
moment a lot of variables are cast to long long.  Windows doesn't
like "long long" and prefers "__int64".  Being two words, I can't
#define my way out of this.

I remember some reason (in kernel space) for this casting.  Some reason
why we couldn't use the pre-defined types.  Anton?  Now we're in
userspace, can we change:

  Dprintf ("Big number %Lu\n", (unsigned long long) num);

to:

  Dprintf ("Big number %Lu\n", (u64) num);

If not, can we not simply #define our types instead of typedef'ing them?

Cheers,
  FlatCap (Rich)
  nt...@fl...

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