Re: [PATCH mini-os enhancements for vtpm 2/8] add posix io to blkfront

[Samuel Thibault <samuel.thibault@ens-lyon.org>]

Matthew Fioravante, le Mon 08 Oct 2012 10:34:24 -0400, a écrit :
> Sometimes n comes out to be BLKIF_MAX_SEGEMENTS_PER_REQUEST +1.
> 
> This happens when your buffer address is sector aligned (512k), but
> not page aligned (4096k).
> So we can either optimize yet again if address is page
> aligned

Ah, right. Well, I'd say it's worth making the effort to test against
that, i.e. (untested)

else {
	if (count >= BLKIF_MAX_SEGMENTS_PER_REQUEST*PAGE_SIZE
	    && (!(buf & ~(PAGE_SIZE-1))))
	    	/* page-aligned */
		bytes = BLKIF_MAX_SEGMENTS_PER_REQUEST*PAGE_SIZE;
	else if (count >= (BLKIF_MAX_SEGMENTS_PER_REQUEST-1)*PAGE_SIZE)
	    	/* only sector-aligned, will have to realign */
		bytes = (BLKIF_MAX_SEGMENTS_PER_REQUEST-1)*PAGE_SIZE;
	else
		bytes = count & ~(blocksize - 1);
    }
}

> Is the page math being done above that assertion correct?

I believe so.

Samuel