[uClinux-dev] Using FAT file system

From: mathias.fritzson@mecel.se
Date: Mon Sep 02 2002 - 09:46:13 EDT 

Hi list

We are by numerous reasons forced to use the FAT filesystem as one of our
filesystems..

My question is if my little fix for compiling FAT support will work or if I
need to do more..


code snippet..   from uClinux-dist/linux-2.0.x/fs/fat/mmap.c

     #ifndef NO_MM

     /*
      * Fill in the supplied page for mmap
      */
     static unsigned long fat_file_mmap_nopage(
          struct vm_area_struct * area,
          unsigned long address,
          int error_code)
     {
          struct inode * inode = area->vm_inode;
          unsigned long page;
          unsigned int clear;
          int pos;
          long gap; /* distance from eof to pos */

          page = __get_free_page(GFP_KERNEL);
          if (!page)
               return page;
          address &= PAGE_MASK;
          pos = address - area->vm_start + area->vm_offset;

          clear = 0;
          gap = inode->i_size - pos;
          if (gap <= 0){
               /* mmaping beyond end of file */
               clear = PAGE_SIZE;
          }else{
               int cur_read;
               int need_read;
               struct file filp;
               if (gap < PAGE_SIZE){
                    clear = PAGE_SIZE - gap;
               }
               filp.f_reada = 0;
               filp.f_pos = pos;
               need_read = PAGE_SIZE - clear;
               {
                    unsigned long cur_fs = get_fs();
                    set_fs (KERNEL_DS);
                    cur_read = fat_file_read (inode,&filp,(char*)page
                         ,need_read);
                    set_fs (cur_fs);
               }
               if (cur_read != need_read){
                    printk ("MSDOS: Error while reading an mmap file %d <> %d\n"
                         ,cur_read,need_read);
               }
          }
          if (clear > 0){
               memset ((char*)page+PAGE_SIZE-clear,0,clear);
          }
          return page;
     }

     struct vm_operations_struct fat_file_mmap = {
          NULL,               /* open */
          NULL,               /* close */
          NULL,               /* unmap */
          NULL,               /* protect */
          NULL,               /* sync */
          NULL,               /* advise */
          fat_file_mmap_nopage,    /* nopage */
          NULL,               /* wppage */
          NULL,               /* swapout */
          NULL,               /* swapin */
     };

     /*
      * This is used for a general mmap of an msdos file
      * Returns 0 if ok, or a negative error code if not.
      */
     int fat_mmap(struct inode * inode, struct file * file, struct vm_area_struct * vma)
     {
          if (vma->vm_flags & VM_SHARED)      /* only PAGE_COW or read-only supported now */
               return -EINVAL;
          if (vma->vm_offset & (inode->i_sb->s_blocksize - 1))
               return -EINVAL;
          if (!inode->i_sb || !S_ISREG(inode->i_mode))
               return -EACCES;
          if (!IS_RDONLY(inode)) {
               inode->i_atime = CURRENT_TIME;
               inode->i_dirt = 1;
          }

          vma->vm_inode = inode;
          inode->i_count++;
          vma->vm_ops = &fat_file_mmap;
          return 0;
     }

     #else /* NO_MM */

     int fat_mmap(struct inode * inode, struct file * file, struct vm_area_struct * vma)  <<<<<< This line was changed from "int fat_mmap()"
     {
          return -ENOSYS;
     }

     #endif /* NO_MM*/

Since I'm not really into the MMU/no MMU layer I'm not sure if this is
enough.. Will the system enter this function at all ??

Cheers

/Mathias


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This archive was generated by hypermail 2.1.4 : Thu Sep 19 2002 - 13:21:47 EDT