[PATCH] pktcdvd: Reduce stack usage

Reduce stack usage in the pkt_start_write() function.  Even though it's not
currently a real problem, the pages and offsets arrays can be eliminated,
which saves approximately 1000 bytes of stack space.
Signed-off-by: Peter Osterlund <petero2@telia.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

drivers/block/pktcdvd.c

@@ -645,7 +645,7 @@ static void pkt_copy_bio_data(struct bio *src_bio, int seg, int offs, struct pag
  * b) The data can be used as cache to avoid read requests if we receive a
  *    new write request for the same zone.
  */
-static void pkt_make_local_copy(struct packet_data *pkt, struct page **pages, int *offsets)
+static void pkt_make_local_copy(struct packet_data *pkt, struct bio_vec *bvec)
 {
 	int f, p, offs;
 
@@ -653,15 +653,15 @@ static void pkt_make_local_copy(struct packet_data *pkt, struct page **pages, in
 	p = 0;
 	offs = 0;
 	for (f = 0; f < pkt->frames; f++) {
-		if (pages[f] != pkt->pages[p]) {
-			void *vfrom = kmap_atomic(pages[f], KM_USER0) + offsets[f];
+		if (bvec[f].bv_page != pkt->pages[p]) {
+			void *vfrom = kmap_atomic(bvec[f].bv_page, KM_USER0) + bvec[f].bv_offset;
 			void *vto = page_address(pkt->pages[p]) + offs;
 			memcpy(vto, vfrom, CD_FRAMESIZE);
 			kunmap_atomic(vfrom, KM_USER0);
-			pages[f] = pkt->pages[p];
-			offsets[f] = offs;
+			bvec[f].bv_page = pkt->pages[p];
+			bvec[f].bv_offset = offs;
 		} else {
-			BUG_ON(offsets[f] != offs);
+			BUG_ON(bvec[f].bv_offset != offs);
 		}
 		offs += CD_FRAMESIZE;
 		if (offs >= PAGE_SIZE) {
@@ -991,18 +991,17 @@ static int pkt_handle_queue(struct pktcdvd_device *pd)
 static void pkt_start_write(struct pktcdvd_device *pd, struct packet_data *pkt)
 {
 	struct bio *bio;
-	struct page *pages[PACKET_MAX_SIZE];
-	int offsets[PACKET_MAX_SIZE];
 	int f;
 	int frames_write;
+	struct bio_vec *bvec = pkt->w_bio->bi_io_vec;
 
 	for (f = 0; f < pkt->frames; f++) {
-		pages[f] = pkt->pages[(f * CD_FRAMESIZE) / PAGE_SIZE];
-		offsets[f] = (f * CD_FRAMESIZE) % PAGE_SIZE;
+		bvec[f].bv_page = pkt->pages[(f * CD_FRAMESIZE) / PAGE_SIZE];
+		bvec[f].bv_offset = (f * CD_FRAMESIZE) % PAGE_SIZE;
 	}
 
 	/*
-	 * Fill-in pages[] and offsets[] with data from orig_bios.
+	 * Fill-in bvec with data from orig_bios.
 	 */
 	frames_write = 0;
 	spin_lock(&pkt->lock);
@@ -1024,11 +1023,11 @@ static void pkt_start_write(struct pktcdvd_device *pd, struct packet_data *pkt)
 			}
 
 			if (src_bvl->bv_len - src_offs >= CD_FRAMESIZE) {
-				pages[f] = src_bvl->bv_page;
-				offsets[f] = src_bvl->bv_offset + src_offs;
+				bvec[f].bv_page = src_bvl->bv_page;
+				bvec[f].bv_offset = src_bvl->bv_offset + src_offs;
 			} else {
 				pkt_copy_bio_data(bio, segment, src_offs,
-						  pages[f], offsets[f]);
+						  bvec[f].bv_page, bvec[f].bv_offset);
 			}
 			src_offs += CD_FRAMESIZE;
 			frames_write++;
@@ -1042,7 +1041,7 @@ static void pkt_start_write(struct pktcdvd_device *pd, struct packet_data *pkt)
 	BUG_ON(frames_write != pkt->write_size);
 
 	if (test_bit(PACKET_MERGE_SEGS, &pd->flags) || (pkt->write_size < pkt->frames)) {
-		pkt_make_local_copy(pkt, pages, offsets);
+		pkt_make_local_copy(pkt, bvec);
 		pkt->cache_valid = 1;
 	} else {
 		pkt->cache_valid = 0;
@@ -1055,17 +1054,9 @@ static void pkt_start_write(struct pktcdvd_device *pd, struct packet_data *pkt)
 	pkt->w_bio->bi_bdev = pd->bdev;
 	pkt->w_bio->bi_end_io = pkt_end_io_packet_write;
 	pkt->w_bio->bi_private = pkt;
-	for (f = 0; f < pkt->frames; f++) {
-		if ((f + 1 < pkt->frames) && (pages[f + 1] == pages[f]) &&
-		    (offsets[f + 1] = offsets[f] + CD_FRAMESIZE)) {
-			if (!bio_add_page(pkt->w_bio, pages[f], CD_FRAMESIZE * 2, offsets[f]))
-				BUG();
-			f++;
-		} else {
-			if (!bio_add_page(pkt->w_bio, pages[f], CD_FRAMESIZE, offsets[f]))
-				BUG();
-		}
-	}
+	for (f = 0; f < pkt->frames; f++)
+		if (!bio_add_page(pkt->w_bio, bvec[f].bv_page, CD_FRAMESIZE, bvec[f].bv_offset))
+			BUG();
 	VPRINTK("pktcdvd: vcnt=%d\n", pkt->w_bio->bi_vcnt);
 
 	atomic_set(&pkt->io_wait, 1);