Re: A problem about DIRECT IO on ext3

[li nux <lnxluv@yahoo.com>]

--- Jens Axboe <axboe@suse.de> wrote:

> On Mon, Oct 17 2005, Grzegorz Kulewski wrote:
> > On Mon, 17 Oct 2005, Jens Axboe wrote:
> > >>how to correct this problem ?
> > >
> > >See your buffer address, it's not aligned. You
> need to align that as
> > >well. This is needed because the hardware will
> dma directly to the user
> > >buffer, and to be on the safe side we require the
> same alignment as the
> > >block layer will normally generate for file
> system io.
> > >
> > >So in short, just align your read buffer to the
> same as your block size
> > >and you will be fine. Example:
> > >
> > >#define BS      (4096)
> > >#define MASK    (BS - 1)
> > >#define ALIGN(buf)      (((unsigned long) (buf) +
> MASK) & ~(MASK))
> > >
> > >char *ptr = malloc(BS + MASK);
> > >char *buf = (char *) ALIGN(ptr);
> > >
> > >read(fd, buf, BS);
> > 
> > Shouldn't one use posix_memalign(3) for that?
> 
> Dunno if one 'should', one 'can' if one wants to. I
> prefer to do it
> manually so I don't have to jump through #define
> hoops to get at it
> (which, btw, still doesn't expose it on this
> machine).
> 
> -- 
> Jens Axboe

Thanx a lot Jens :-)
Its working now.
I did not have to make these adjustments on 2.6
Is looks to be having more relaxation.

Can somebody please throw some light on how to find
your system's hard/soft block size ?


	
		
__________________________________ 
Yahoo! Mail - PC Magazine Editors' Choice 2005 
http://mail.yahoo.com