> Default read/write inerfaces does not move file's data to process address space ?
Yes it does, in either case, user space memory has to be in process address space. But Difference is in the access pattern. With read/write, you demand for it explicitly through a system call, hence application is more involved here. While for mmap access, all transfer happens in application-unaware mechanism, with page-fault handlers inside kernel. Application just access mapped buffers like memory array and magic happens inside kernel as you keep on accessing bytes.On Fri, Jan 11, 2013 at 3:31 AM, horseriver <horserivers@xxxxxxxxx> wrote:
On Fri, Jan 11, 2013 at 12:39:26PM +0530, Rajat Sharma wrote:Default read/write inerfaces does not move file's data to process address space ?
> 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.
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@xxxxxxxxx> 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!
> >
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