[Bug 243178] newfs_msdos: wrong FAT type determination

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=243178

--- Comment #4 from Damjan Jovanovic <damjan.jov@gmail.com> ---
newfs_msdos: 65503 clusters too few clusters for FAT32, need 65525

---snip---
    593     if (cls < mincls(fat)) {
    594         warnx("%u clusters too few clusters for FAT%u, need %u", cls,
fat,
    595             mincls(fat));
    596         goto done;
    597     }
---snip---

so cls=65503, fat=32, mincls(fat)=65525.

---snip---
     71 #define MINCLS12  1U            /* minimum FAT12 clusters */
     72 #define MINCLS16  0xff5U        /* minimum FAT16 clusters */
     73 #define MINCLS32  0xfff5U       /* minimum FAT32 clusters */
     74 #define MAXCLS12  0xff4U        /* maximum FAT12 clusters */
     75 #define MAXCLS16  0xfff4U       /* maximum FAT16 clusters */
     76 #define MAXCLS32  0xffffff4U    /* maximum FAT32 clusters */
     77 
     78 #define mincls(fat)  ((fat) == 12 ? MINCLS12 :  \
     79                       (fat) == 16 ? MINCLS16 :  \
     80                                     MINCLS32)
---snip---

Note how these form consecutive non-overlapping ranges:

0x1 - 0xff4|0xff5 - 0xfff4|0xfff5 - 0xffffff4
 FAT12     |    FAT16     |     FAT32

So the wrong kind of FAT was chosen for that number of clusters, it should have
used FAT16, and when FAT16 is manually forced, it works.

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