Question about do_sync_read()

Question about do_sync_read()

[Manish Katiyar]

Hi,

In the implementation of file systems for 2.6 kernels,
generic_file_read is often replaced with do_sync_read(). In this
function we call "filp->f_op->aio_read" unconditionally.
where most of the times aio_read is intialized as
generic_file_aio_read(). Wouldn't it be a good idea to change the
following code

241  for (;;) {
242   ret = filp->f_op->aio_read(&kiocb, &iov, 1, kiocb.ki_pos);
243   if (ret != -EIOCBRETRY)
244    break;
245   wait_on_retry_sync_kiocb(&kiocb);

to

241  for (;;) {
242     if(filp->f_op->aio_read)
243         ret = filp->f_op->aio_read(&kiocb, &iov, 1, kiocb.ki_pos);
244     else
245              ret = generic_file_aio_read(&kiocb, &iov, 1, kiocb.ki_pos);
246   if (ret != -EIOCBRETRY)
247    break;
248   wait_on_retry_sync_kiocb(&kiocb);

Just to have a fall back mechanism as we do at many places in the VFS layer..

-- 
Thanks & Regards,
********************************************
Manish Katiyar  ( http://mkatiyar.googlepages.com )
3rd Floor, Fair Winds Block
EGL Software Park
Off Intermediate Ring Road
Bangalore 560071, India
***********************************************

Re: Question about do_sync_read()

[Benny Halevy]

On Feb. 09, 2008, 10:52 +0200, "Manish Katiyar" <mkatiyar@gmail.com> wrote:
> Hi,
> 
> In the implementation of file systems for 2.6 kernels,
> generic_file_read is often replaced with do_sync_read(). In this
> function we call "filp->f_op->aio_read" unconditionally.
> where most of the times aio_read is intialized as
> generic_file_aio_read(). Wouldn't it be a good idea to change the
> following code
> 
> 241  for (;;) {
> 242   ret = filp->f_op->aio_read(&kiocb, &iov, 1, kiocb.ki_pos);
> 243   if (ret != -EIOCBRETRY)
> 244    break;
> 245   wait_on_retry_sync_kiocb(&kiocb);
> 
> to
> 
> 241  for (;;) {
> 242     if(filp->f_op->aio_read)
> 243         ret = filp->f_op->aio_read(&kiocb, &iov, 1, kiocb.ki_pos);
> 244     else
> 245              ret = generic_file_aio_read(&kiocb, &iov, 1, kiocb.ki_pos);
> 246   if (ret != -EIOCBRETRY)
> 247    break;
> 248   wait_on_retry_sync_kiocb(&kiocb);
> 
> Just to have a fall back mechanism as we do at many places in the VFS layer..
> 

FWIW, it's a bit more efficient to set aio_read to generic_file_aio_read and
call it unconditionally.

Benny