Question about do_sync_read()

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
***********************************************
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Re: Question about do_sync_read()

On Feb. 09, 2008, 10:52 +0200, "Manish Katiyar" 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

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