fatfs/doc/img/app3.c

   1 /*----------------------------------------------------------------------/
   2 / Allocate a contiguous area to the file
   3 /-----------------------------------------------------------------------/
   4 / This function checks if the file is contiguous with desired size.
   5 / If not, a block of contiguous sectors is allocated to the file.
   6 / If the file has been opened without FA_WRITE flag, it only checks if
   7 / the file is contiguous and returns the resulut. */
   8
   9 #if _FATFS != 80367 /* Check if R0.10c */
  10 #error This function may not be compatible with this revision of FatFs module.
  11 #endif
  12
  13 /* Declarations of FatFs internal functions accessible from applications.
  14 /  This is intended to be used for disk checking/fixing or dirty hacks :-) */
  15 DWORD clust2sect (FATFS* fs, DWORD clst);
  16 DWORD get_fat (FATFS* fs, DWORD clst);
  17 FRESULT put_fat (FATFS* fs, DWORD clst, DWORD val);
  18
  19
  20 DWORD allocate_contiguous_clusters (    /* Returns the first sector in LBA (0:error or not contiguous) */
  21     FIL* fp,    /* Pointer to the open file object */
  22     DWORD len   /* Number of bytes to allocate */
  23 )
  24 {
  25     DWORD csz, tcl, ncl, ccl, cl;
  26
  27
  28     if (f_lseek(fp, 0) || !len)     /* Check if the given parameters are valid */
  29         return 0;
  30     csz = 512UL * fp->fs->csize;    /* Cluster size in unit of byte (assuming 512 bytes/sector) */
  31     tcl = (len + csz - 1) / csz;    /* Total number of clusters required */
  32     len = tcl * csz;                /* Round-up file size to the cluster boundary */
  33
  34     /* Check if the existing cluster chain is contiguous */
  35     if (len == fp->fsize) {
  36         ncl = 0; ccl = fp->sclust;
  37         do {
  38             cl = get_fat(fp->fs, ccl);  /* Get the cluster status */
  39             if (cl + 1 < 3) return 0;   /* Hard error? */
  40             if (cl != ccl + 1 &&; cl < fp->fs->n_fatent) break;  /* Not contiguous? */
  41             ccl = cl;
  42         } while (++ncl < tcl);
  43         if (ncl == tcl)             /* Is the file contiguous? */
  44             return clust2sect(fp->fs, fp->sclust);  /* Return file start sector */
  45     }
  46 #if _FS_READONLY
  47     return 0;
  48 #else
  49     if (f_truncate(fp)) return 0;   /* Remove the existing chain */
  50
  51     /* Find a free contiguous area */
  52     ccl = cl = 2; ncl = 0;
  53     do {
  54         if (cl >= fp->fs->n_fatent) return 0;   /* No contiguous area is found. */
  55         if (get_fat(fp->fs, cl)) {  /* Encounterd a cluster in use */
  56             do {    /* Skip the block of used clusters */
  57                 cl++;
  58                 if (cl >= fp->fs->n_fatent) return 0;   /* No contiguous area is found. */
  59             } while (get_fat(fp->fs, cl));
  60             ccl = cl; ncl = 0;
  61         }
  62         cl++; ncl++;
  63     } while (ncl < tcl);
  64
  65     /* Create a contiguous cluster chain */
  66     fp->fs->last_clust = ccl - 1;
  67     if (f_lseek(fp, len)) return 0;
  68
  69     return clust2sect(fp->fs, fp->sclust);  /* Return file start sector */
  70 #endif
  71 }
  72
  73
  74 int main (void)
  75 {
  76     FRESULT fr;
  77     DRESULT dr;
  78     FATFS fs;
  79     FIL fil;
  80     DWORD org;
  81
  82
  83     /* Open or create a file */
  84     f_mount(&fs, "", 0);
  85     fr = f_open(&fil, "swapfile.sys", FA_READ | FA_WRITE | FA_OPEN_ALWAYS);
  86     if (fr) return 1;
  87
  88     /* Check if the file is 64MB in size and occupies a contiguous area.
  89     /  If not, a contiguous area will be re-allocated to the file. */
  90     org = allocate_contiguous_clusters(&fil, 0x4000000);
  91     if (!org) {
  92         printf("Function failed due to any error or insufficient contiguous area.\n");
  93         f_close(&fil);
  94         return 1;
  95     }
  96
  97     /* Now you can read/write the file with disk functions bypassing the file system layer. */
  98
  99     dr = disk_write(fil.fs->drv, Buff, org, 1024);   /* Write 512KiB from top of the file */
 100
 101     ...
 102
 103     f_close(&fil);
 104     return 0;
 105 }
 106