internel implemention of file operation

[horseriver]

On Fri, Jan 11, 2013 at 12:39:26PM +0530, Rajat Sharma wrote:

> Default read/write inerfaces are better suited for sequential read/write
> within your program. Although you can seek to any location within the file,
> you still have overhead to issue system calls to get data. However mmap
> allows you to map a section of file into program address space. 

  Default read/write inerfaces does not move file's data to process address space ?

  when  r/w a file descript which returnd by open() , how do the file data move from one place to another place ?

  For each time the write function being  called  , will kernel  call filesystem's driver's write  to respond  ??
  In my opinion,kernel will passed a  buffer's head address  which is passed form user-layer into driver,then driver will fill this buffer with file's
  data which is got by filesystem's read operation ?

  Am I right?   
  
  Thanks! 
> 
> 
> -Rajat
> 
> 
> On Fri, Jan 11, 2013 at 2:44 AM, horseriver <horserivers at gmail.com> wrote:
> 
> > hi:
> >
> >   these two wayes of operating one file :
> >
> >   1.use open/write interface call .
> >
> >   2.mmap this file into memory , then access this memory area and do r/w .
> >
> >   what is the essential difference between this teo wayes?
> >
> > thanks!
> >