[SOLVED] How to get an access to data has been read in the custom bi_end_io routine ?

dr.SysMan · 12-28-2017, 08:06 AM

Hello!

I developing a small block layered driver for Linux ...

I use my own bi_end_io() routine to intercept a data has been read from other block/disk device. So, my routine looks like:

Code:

static	void	__iob_xxx	(
		struct bio *	iob
			)
{
struct bio_vec	bvec = {0};
struct	bvec_iter iter = {0};
sector_t	lbn, nlbn;

	bio_for_each_segment(bvec, iob, iter)
		{
		char *	iobuf;

		iobuf = __bio_kmap_atomic(iob, iter);

		$TRACE("#%02d: page=%p, off=%u, len=%u, iobuf=%p, lbn=%lu",
			iter.bi_idx, bvec.bv_page, bvec.bv_offset, bvec.bv_len, iobuf, iter.bi_sector);


		__bio_kunmap_atomic(iob);
		}
}


static	void	dua_bio_end_io	(
			struct bio *	iob
				)
{
IOB_ARGS * iob_args;

	iob_args = iob->bi_private;

	iob->bi_end_io = iob_args->bi_end_io;
	iob->bi_private = iob_args->bi_private;

	__ret_iob_args (iob_args);

	if ( bio_data_dir(iob) == READ )
		__iob_xxx (iob);

	if ( iob->bi_end_io )
		iob->bi_end_io (iob);

}

So the bio_for_each_segment don't do anything .
What I/m need to check additionaly ?
Do I'm need to set in the make_request_fn() routine for the bio additionaly

Thanks!

dr.SysMan · 12-28-2017, 09:20 AM

Some additions, it looks like that bvecs has been cleared before calling my bi_end_io() routine.
I expects that my bi_end_io() routine is calling before original bi_end_io(), but seems that it's not so.

Code:

static blk_qc_t dua_make_request_fn	(
		struct request_queue *	ioq,
			struct bio *	iob
				)
{
int	status = 0;

	if ( bio_data_dir(iob) == WRITE )
		__iob_xxx(iob);

	/*
	 * A handling of the READ request is require 'enqueue read request' & 'wait for read completion' paradigm,
	 * so we need to allocate IOB_ARGS block to carry data to the "Read Completion I/O" routine.
	 */
	else if ( bio_data_dir(iob) == READ )
		{
		IOB_ARGS *iob_args = NULL;

		if ( __get_iob_args (&iob_args) )
			{
			printk(KERN_ERR  __MODULE__ ": Buffered I/O quota limit has been exhausted\n");

			iob->bi_error = -EBUSY;
			bio_endio(iob);
			}

		iob_args->bi_end_io = iob->bi_end_io;
		iob_args->bi_private = iob->bi_private;

		/*
		 * Replace an address of the Completion I/O routine for 'read' operation,
		 * save original address.
		 */
		iob->bi_private = iob_args;
		iob->bi_end_io = dua_bio_end_io;
		}

	/* Just for sanity check ... */
	else	{
		printk(KERN_WARNING  __MODULE__ ": Unhandled I/O request %d\n", bio_data_dir(iob) );
		}


	/* Call original make_reques_fn() to performs a main work ... */
	status = backend_make_request_fn(ioq, iob);

	return	status;
}

Thanks for any ideas!

dr.SysMan · 01-11-2018, 07:01 AM

Hi !

A solution is the replacing a dumb macro ( bio_for_each_segment(bvec, iob, iter) ) with old school "for", see follows:

Code:

...
	/* Do each segment independently. */
	for (i = 0, bvl = iob->bi_io_vec; i < iob->bi_vcnt; i++, bvl++)
		{
		void	 *kaddr = kmap_atomic(bvl->bv_page), *iobuf;

		iobuf	= kaddr + bvl->bv_offset;

		nlbn	= bvl->bv_len/DUDRV$K_SECTORSZ;


		for ( ;nlbn; nlbn--, lbn++ , iobuf += DUDRV$K_SECTORSZ)
			{
                         ...
			}

		kunmap_atomic(kaddr);
	}
}