dg_unbuffered_read(2)             SDK R4.11            dg_unbuffered_read(2)


NAME
       dgunbufferedread - synchronously read data from a file without
       system buffering

SYNOPSIS
       int dgunbufferedread (fildes, buffer, startblock, numblocks)
       int       fildes;
       char      buffer[];
       unsigned  startblock;
       unsigned  numblocks;

   where:
       fildes         A valid descriptor
       buffer         User data buffer
       startblock    Starting logical block number
       numblocks     Size (in blocks) of the read

DESCRIPTION
       The dgunbufferedread system call transfers numblocks blocks of
       data from the file associated with fildes into the buffer pointed to
       by buffer.  The starting block number of the transfer is given by the
       startblock parameter.

       The file position attribute of fildes is ignored by this interface.
       The starting block position of the read must be specified in the
       call.  The file position attribute of fildes remains unchanged by the
       execution of this call.

       If mandatory record locking is enabled for the file, this call will
       fail.

ACCESS CONTROL
       The fildes must have been opened for unbuffered I/O with the
       O_DG_UNBUFFERED flag, and fildes must also have been opened for read
       access.

RETURN VALUE
       0..numblocks
              Completed successfully.  The number of blocks actually read is
              returned.  The value 0 indicates EOF (end-of-file).

       -1     An error occurred.  errno is set to indicate the error.

DIAGNOSTICS
       Errno may be set to one of the following error codes:

       EBADF     fildes is not opened for unbuffered reading.

       EFAULT    buffer points outside the allocated address space.

       EINTR     A signal was caught during the system call.

SEE ALSO
       open(2), dgunbufferedwrite(2).


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