ore: Support for raid 6

This simple patch adds support for raid6 to the ORE.
Most operations and calculations where already for the general
case. Only things left:
* call async_gen_syndrome() in the case of raid6
  (NOTE that the raid6 math is the one supported by the Linux Kernel
   see: crypto/async_tx/async_pq.c)
* call _ore_add_parity_unit() twice with only last call generating
  the redundancy pages.

* Fix couple BUGS in old code
  a. In reads when parity==2 it can happen that per_dev->length=0
     but per_dev->offset was set and adjusted by _ore_add_sg_seg().
     Don't let it be overwritten.
  b. The all 'cur_comp > starting_dev' thing to determine if:
       "per_dev->offset is in the current stripe number or the
       next one."
     Was a complete raid5/4 accident. When parity==2 this is not
     at all true usually. All we need to do is increment si->ob_offset
     once we pass by the first parity device.
     (This also greatly simplifies the code, amen)
  c. Calculation of si->dev rotation can overflow when parity==2.

* Then last enable raid6 in ore_verify_layout()

I want to deeply thank Daniel Gryniewicz who found first all the
bugs in the old raid code, and inspired these patches:
	Inspired-by Daniel Gryniewicz <dang@linuxbox.com>

Signed-off-by: Boaz Harrosh <bharrosh@panasas.com>

1 files changed, 24 insertions, 13 deletions

diff --git a/fs/exofs/ore_raid.c b/fs/exofs/ore_raid.c
index d58a952e28bc..7f20f25c232c 100644
--- a/fs/exofs/ore_raid.c
+++ b/fs/exofs/ore_raid.c
@@ -218,20 +218,28 @@ static unsigned _sp2d_max_pg(struct __stripe_pages_2d *sp2d)
 static void _gen_xor_unit(struct __stripe_pages_2d *sp2d)
 {
 	unsigned p;
+	unsigned tx_flags = ASYNC_TX_ACK;
+
+	if (sp2d->parity == 1)
+		tx_flags |= ASYNC_TX_XOR_ZERO_DST;
+
 	for (p = 0; p < sp2d->pages_in_unit; p++) {
 		struct __1_page_stripe *_1ps = &sp2d->_1p_stripes[p];
 
 		if (!_1ps->write_count)
 			continue;
 
-		init_async_submit(&_1ps->submit,
-			ASYNC_TX_XOR_ZERO_DST | ASYNC_TX_ACK,
+		init_async_submit(&_1ps->submit, tx_flags,
 			NULL, NULL, NULL, (addr_conv_t *)_1ps->scribble);
 
-		/* TODO: raid6 */
-		_1ps->tx = async_xor(_1ps->pages[sp2d->data_devs], _1ps->pages,
-				     0, sp2d->data_devs, PAGE_SIZE,
-				     &_1ps->submit);
+		if (sp2d->parity == 1)
+			_1ps->tx = async_xor(_1ps->pages[sp2d->data_devs],
+						_1ps->pages, 0, sp2d->data_devs,
+						PAGE_SIZE, &_1ps->submit);
+		else /* parity == 2 */
+			_1ps->tx = async_gen_syndrome(_1ps->pages, 0,
+						sp2d->data_devs + sp2d->parity,
+						PAGE_SIZE, &_1ps->submit);
 	}
 
 	for (p = 0; p < sp2d->pages_in_unit; p++) {
@@ -616,7 +624,7 @@ static int _read_4_write_execute(struct ore_io_state *ios)
 int _ore_add_parity_unit(struct ore_io_state *ios,
 			    struct ore_striping_info *si,
 			    struct ore_per_dev_state *per_dev,
-			    unsigned cur_len)
+			    unsigned cur_len, bool do_xor)
 {
 	if (ios->reading) {
 		if (per_dev->cur_sg >= ios->sgs_per_dev) {
@@ -641,9 +649,11 @@ int _ore_add_parity_unit(struct ore_io_state *ios,
 			/* If first stripe, Read in all read4write pages
 			 * (if needed) before we calculate the first parity.
 			 */
-			_read_4_write_first_stripe(ios);
+			if (do_xor)
+				_read_4_write_first_stripe(ios);
 		}
-		if (!cur_len) /* If last stripe r4w pages of last stripe */
+		if (!cur_len && do_xor)
+			/* If last stripe r4w pages of last stripe */
 			_read_4_write_last_stripe(ios);
 		_read_4_write_execute(ios);
 
@@ -655,7 +665,7 @@ int _ore_add_parity_unit(struct ore_io_state *ios,
 			++(ios->cur_par_page);
 		}
 
-		BUG_ON(si->cur_comp != sp2d->data_devs);
+		BUG_ON(si->cur_comp < sp2d->data_devs);
 		BUG_ON(si->cur_pg + num_pages > sp2d->pages_in_unit);
 
 		ret = _ore_add_stripe_unit(ios,  &array_start, 0, pages,
@@ -663,9 +673,10 @@ int _ore_add_parity_unit(struct ore_io_state *ios,
 		if (unlikely(ret))
 			return ret;
 
-		/* TODO: raid6 if (last_parity_dev) */
-		_gen_xor_unit(sp2d);
-		_sp2d_reset(sp2d, ios->r4w, ios->private);
+		if (do_xor) {
+			_gen_xor_unit(sp2d);
+			_sp2d_reset(sp2d, ios->r4w, ios->private);
+		}
 	}
 	return 0;
 }