Add FAT size calculation

git-svn-id: svn://svn.code.sf.net/p/nuttx/code/trunk@803 42af7a65-404d-4744-a932-0658087f49c3

fs/fat/fs_configfat.c

@@ -56,15 +56,198 @@
  ****************************************************************************/
 
 /****************************************************************************
- * Name: 
+ * Name:  mkfatfs_nfatsect12
  *
  * Description:
+ *   Calculate the number of sectors need for the fat in a FAT12 file system.
  *
  * Input:
+ *   fmt - Caller specified format parameters
+ *   var - Other format parameters that are not caller specifiable. (Most
+ *     set by mkfatfs_configfatfs()).
+ *   navailsects - The number of sectors available for both FAT and data.
+ *     This is a precalculated value equal to the total number of sectors
+ *     minus the number of root directory sectors and minus the number of
+ *     reserved sectors.
  *
  * Return:
+ *   0: That calculation would have overflowed
+ *  >0: The total size of the FAT in sectors.
  *
  ****************************************************************************/
+static inline uint32 mkfatfs_nfatsect12(FAR struct fat_format_s *fmt,
+                                        FAR struct fat_var_s *var,
+                                        uint32 navailsects)
+{
+   uint32 denom ;
+   uint32 numer;
+
+  /* For FAT12, the cluster number is held in a 12-bit number or 1.5 bytes per
+   * cluster reference.  So each FAT sector will hold sectorsize/1.5 cluster
+   * references (except for the first sector of each FAT which has two reserved
+   * 12-bit values).  And the total number of FAT sectors needed is:
+   *
+   *   nfatsects = nfats * (1.5 * (ndataclust + 2) / sectorsize)
+   *
+   * where:
+   *
+   *   ndataclust = ndatasect / clustsize
+   *   nvailsects = nfatsects + ndatasect
+   *
+   * The solution to this set of linear equations is:
+   *
+   *   nfatsects  = nfats * (3 * navailsects + 6 * clustersize) / 
+   *                        (3 * nfats + 2 * sectorsize * clustersize)
+   *
+   * The numerator would overflow uint32 if:
+   *
+   *   3 * navailsects + 6 * clustersize > 0xffffffff
+   *
+   * Or 
+   *
+   *   navailsects > 0x55555555 - 2 * clustersize
+   */
+
+  if (navailsects <= (0x55555555 - (1 << (fmt->ff_clustshift + 1))))
+    {
+      denom = (fmt->ff_nfats << 1) + fmt->ff_nfats
+            + (var->fv_sectorsize << (fmt->ff_clustshift + 1));
+      numer = (navailsects << 1) + navailsects
+            + (1 << (fmt->ff_clustshift + 2)) + (1 << (fmt->ff_clustshift + 1));
+      return fmt->ff_nfats * (numer + denom - 1) / denom;
+    }
+  else
+    {
+      return 0;
+    }
+}
+
+/****************************************************************************
+ * Name:  mkfatfs_nfatsect16
+ *
+ * Description:
+ *   Calculate the number of sectors need for the fat in a FAT16 file system.
+ *
+ * Input:
+ *   fmt - Caller specified format parameters
+ *   var - Other format parameters that are not caller specifiable. (Most
+ *     set by mkfatfs_configfatfs()).
+ *   navailsects - The number of sectors available for both FAT and data.
+ *     This is a precalculated value equal to the total number of sectors
+ *     minus the number of root directory sectors and minus the number of
+ *     reserved sectors.
+ *
+ * Return:
+ *    The total size of the FAT in sectors.
+ *
+ ****************************************************************************/
+static inline uint32 mkfatfs_nfatsect16(FAR struct fat_format_s *fmt,
+                                        FAR struct fat_var_s *var,
+                                        uint32 navailsects)
+{
+   uint32 denom;
+   uint32 numer;
+
+  /* For FAT16, the cluster number is held in a 16-bit number or 2 bytes per
+   * cluster reference.  So each FAT sector will hold sectorsize/2 cluster
+   * references (except for the first sector of each FAT which has two reserved
+   * 16-bit values).  And the total number of FAT sectors needed is:
+   *
+   *   nfatsects = nfats * (2 * (ndataclust + 2) / sectorsize)
+   *
+   * where:
+   *
+   *   ndataclust = ndatasect / clustsize
+   *   nvailsects = nfatsects + ndatasect
+   *
+   * The solution to this set of linear equations is:
+   *
+   *   nfatsects  = nfats * (navailsects + 2 * clustersize) / 
+   *                        (nfats + sectorsize * clustersize / 2)
+   *
+   * Overflow in the calculation of the numerator could occur if:
+   *
+   *   navailsects > 0xffffffff - 2 * clustersize
+   */
+
+  if (fmt->ff_clustshift == 0)
+    {
+      denom = fmt->ff_nfats + (var->fv_sectorsize >> 1);
+      numer = navailsects + 2;
+    }
+  else
+    {
+      denom = fmt->ff_nfats + (var->fv_sectorsize << (fmt->ff_clustshift - 1));
+      numer = navailsects + (1 << (fmt->ff_clustshift + 1));
+    }
+  return fmt->ff_nfats * (numer + denom - 1) / denom;
+}
+
+/****************************************************************************
+ * Name:  mkfatfs_nfatsect32
+ *
+ * Description:
+ *   Calculate the number of sectors need for the fat in a FAT32 file system.
+ *
+ * Input:
+ *   fmt - Caller specified format parameters
+ *   var - Other format parameters that are not caller specifiable. (Most
+ *     set by mkfatfs_configfatfs()).
+ *   navailsects - The number of sectors available for both FAT and data.
+ *     This is a precalculated value equal to the total number of sectors
+ *     minus the number of root directory sectors and minus the number of
+ *     reserved sectors.
+ *
+ * Return:
+ *   The total size of the FAT in sectors.
+ *
+ ****************************************************************************/
+static inline uint32 mkfatfs_nfatsect32(FAR struct fat_format_s *fmt,
+                                        FAR struct fat_var_s *var,
+                                        uint32 navailsects)
+{
+   uint32 denom;
+   uint32 numer;
+
+  /* For FAT32, the cluster number is held in a 32-bit number or 4 bytes per
+   * cluster reference.  So each FAT sector will hold sectorsize/4 cluster
+   * references (except for the first sector of each FAT which has three reserved
+   * 32-bit values).  And the total number of FAT sectors needed is:
+   *
+   *   nfatsects = nfats * (4 * (ndataclust + 3) / sectorsize)
+   *
+   * where:
+   *
+   *   ndataclust = ndatasect / clustsize
+   *   nvailsects = nfatsects + ndatasect
+   *
+   * The solution to this set of linear equations is:
+   *
+   *   nfatsects  = nfats * (navailsects + 3 * clustersize) / 
+   *                        (nfats + sectorsize * clustersize / 4)
+   *
+   * Overflow in the calculation of the numerator could occur if:
+   *
+   *   navailsects > 0xffffffff - 3 * clustersize
+   */
+
+  if (fmt->ff_clustshift == 0)
+    {
+      denom = fmt->ff_nfats + (var->fv_sectorsize >> 2);
+      numer = navailsects + 3;
+    }
+  else if (fmt->ff_clustshift == 1)
+    {
+      denom = fmt->ff_nfats + (var->fv_sectorsize >> 1);
+      numer = navailsects + 6;
+    }
+  else
+    {
+      denom = fmt->ff_nfats + (var->fv_sectorsize << (fmt->ff_clustshift - 2));
+      numer = navailsects + (1 << (fmt->ff_clustshift + 1)) + (1 << fmt->ff_clustshift);
+    }
+   return fmt->ff_nfats * (numer + denom - 1) / denom;
+}
 
 /****************************************************************************
  * Global Functions

fs/fat/fs_mkfatfs.h

@@ -99,12 +99,13 @@ struct fat_var_s
    ubyte         fv_jump[3];        /* 3-byte boot jump instruction */
    ubyte         fv_sectshift;      /* Log2 of fv_sectorsize */
    ubyte         fv_nrootdirsects;  /* Number of root directory sectors */
+   ubyte         fv_fatsize;        /* FAT size: 0 (not determined), 12, 16, or 32 */
    uint16        fv_bootcodesize;   /* Size of array at fv_bootcode */
    uint32        fv_createtime;     /* Creation time */
    uint32        fv_sectorsize;     /* Size of one hardware sector */
    uint32        fv_nsectors;       /* Number of sectors */
    uint32        fv_nfatsects;      /* Number of sectors in each FAT */
-   uint32        fv_clustcount;     /* Number of clusters */
+   uint32        fv_nclusters;      /* Number of clusters */
    ubyte        *fv_sect;           /* Allocated working sector buffer */
    const ubyte  *fv_bootcode;       /* Points to boot code to put into MBR */
 };

fs/fat/fs_writefat.c

@@ -88,7 +88,7 @@ static inline void mkfatfs_initmbr(FAR struct fat_format_s *fmt,
 
   /* 1@13: Sectors per allocation unit: 2**n, n=0..7 */
 
-  MBR_PUTSECPERCLUS(var->fv_sect, fmt->ff_clustsize);
+  MBR_PUTSECPERCLUS(var->fv_sect, (1 << fmt->ff_clustshift));
 
   /* 2@14: Reserved sector count: Usually 32 */
 
@@ -250,7 +250,7 @@ static inline void mkfatfs_initfsinfo(FAR struct fat_format_s *fmt,
 
   /* 4@488: Last free cluster count on volume */
 
-  FSI_PUTFREECOUNT(var->fv_sect, var->fv_clustcount - 1);
+  FSI_PUTFREECOUNT(var->fv_sect, var->fv_nclusters - 1);
 
   /* 4@492: Cluster number of 1st free cluster */
 

include/nuttx/mkfatfs.h

@@ -49,7 +49,7 @@
 
 #define MKFATFS_DEFAULT_BBCHECK      FALSE /* FALSE: No bad block check */
 #define MKFATFS_DEFAULT_NFATS        2     /* 2: Default number of FATs */
-#define MKFATFS_DEFAULT_FATSIZE      0     /* 0: Autoselect FAT size */
+#define MKFATFS_DEFAULT_FATSIZE      0xff  /* 0: Autoselect FAT size */
 #define MKFATFS_DEFAULT_CLUSTSIZE    0     /* 0: Autoselect cluster size */
 #define MKFATFS_DEFAULT_VOLUMELABEL  { ' ', ' ', ' ', ' ', ' ', ' ', ' ', ' ', ' ', ' ', ' ' }
 #define MKFATFS_DEFAULT_BKUPBOOT     0     /* 0: Determine sector number of the backup boot sector */
@@ -86,7 +86,7 @@ struct fat_format_s
 {
    ubyte   ff_nfats;           /* Number of FATs */
    ubyte   ff_fatsize;         /* FAT size: 0 (autoselect), 12, 16, or 32 */
-   ubyte   ff_clustsize;       /* Number of sectors per cluster: 0 (autoselect) */
+   ubyte   ff_clustshift;      /* Log2 of sectors per cluster: 0-5, 0xff (autoselect) */
    ubyte   ff_volumelabel[11]; /* Volume label */
    uint16  ff_backupboot;      /* Sector number of the backup boot sector (0=use default)*/
    uint16  ff_rootdirentries;  /* Number of root directory entries */