servers/pfs/read.c

   1 #include "fs.h"
   2 #include "buf.h"
   3 #include <minix/com.h>
   4 #include "inode.h"
   5
   6
   7 /*===========================================================================*
   8  *                              fs_readwrite                                 *
   9  *===========================================================================*/
  10 int fs_readwrite(message *fs_m_in, message *fs_m_out)
  11 {
  12   int r, rw_flag;
  13   struct buf *bp;
  14   cp_grant_id_t gid;
  15   off_t position, f_size;
  16   unsigned int nrbytes, cum_io;
  17   mode_t mode_word;
  18   struct inode *rip;
  19   ino_t inumb;
  20
  21   r = OK;
  22   cum_io = 0;
  23   inumb = (ino_t) fs_m_in->REQ_INODE_NR;
  24
  25   /* Find the inode referred */
  26   if ((rip = find_inode(inumb)) == NULL) return(EINVAL);
  27
  28   mode_word = rip->i_mode & I_TYPE;
  29   if (mode_word != I_NAMED_PIPE) return(EIO);
  30   f_size = rip->i_size;
  31
  32   /* Get the values from the request message */
  33   rw_flag = (fs_m_in->m_type == REQ_READ ? READING : WRITING);
  34   gid = (cp_grant_id_t) fs_m_in->REQ_GRANT;
  35   position = fs_m_in->REQ_SEEK_POS_LO;
  36   nrbytes = (unsigned) fs_m_in->REQ_NBYTES;
  37
  38   /* We can't read beyond the max file position */
  39   if (nrbytes > MAX_FILE_POS) return(EFBIG);
  40
  41   if (rw_flag == WRITING) {
  42           /* Check in advance to see if file will grow too big. */
  43           /* Casting nrbytes to signed is safe, because it's guaranteed not to
  44              be beyond max signed value (i.e., MAX_FILE_POS). */
  45           if (position > PIPE_BUF - (signed) nrbytes) return(EFBIG);
  46   }
  47
  48   /* Mark inode in use */
  49   if ((get_inode(rip->i_dev, rip->i_num)) == NULL) return(err_code);
  50   if ((bp = get_block(rip->i_dev, rip->i_num)) == NULL) return(err_code);
  51
  52   if (rw_flag == READING) {
  53         /* Copy a chunk from the block buffer to user space. */
  54         r = sys_safecopyto(VFS_PROC_NR, gid, (vir_bytes) 0,
  55                 (vir_bytes) (bp->b_data+position), (size_t) nrbytes);
  56   } else {
  57         /* Copy a chunk from user space to the block buffer. */
  58         r = sys_safecopyfrom(VFS_PROC_NR, gid, (vir_bytes) 0,
  59                 (vir_bytes) (bp->b_data+position), (size_t) nrbytes);
  60   }
  61
  62   if (r == OK) {
  63         position += (signed) nrbytes; /* Update position */
  64         cum_io += nrbytes;
  65   }
  66
  67   fs_m_out->RES_SEEK_POS_LO = position; /* It might change later and the VFS
  68                                            has to know this value */
  69
  70   /* On write, update file size and access time. */
  71   if (rw_flag == WRITING) {
  72           if (position > f_size) rip->i_size = position;
  73   } else {
  74         if(position >= rip->i_size) {
  75                 /* All data in the pipe is read, so reset pipe pointers */
  76                 rip->i_size = 0;        /* no data left */
  77                 position = 0;           /* reset reader(s) */
  78         }
  79   }
  80
  81   bp->b_bytes = position;
  82   if (rw_flag == READING) rip->i_update |= ATIME;
  83   if (rw_flag == WRITING) rip->i_update |= CTIME | MTIME;
  84   fs_m_out->RES_NBYTES = (size_t) cum_io;
  85   put_inode(rip);
  86   put_block(rip->i_dev, rip->i_num);
  87
  88   return(r);
  89 }