[PATCH 3/6] SQUASHME: pmem: Streamline pmem driver

[Boaz Harrosh <boaz@plexistor.com>]

remove 89 lines of code to do a single memcpy. The reason
this was so in brd (done badly BTW) is because destination
memory is page-by-page based. With pmem we have the destination
contiguous so we can do any size, in one go.

[v2]
Remove the BUG_ON checks on out of range IO.
The core already does these checks and I did not see these
checks done in other drivers.

Signed-off-by: Boaz Harrosh <boaz@plexistor.com>
---
 drivers/block/pmem.c | 112 ++++++++++-----------------------------------------
 1 file changed, 22 insertions(+), 90 deletions(-)

diff --git a/drivers/block/pmem.c b/drivers/block/pmem.c
index dcb524f..6a45fd5 100644
--- a/drivers/block/pmem.c
+++ b/drivers/block/pmem.c
@@ -44,91 +44,15 @@ struct pmem_device {
 static int pmem_major;
 static atomic_t pmem_index;
 
-/*
- * direct translation from (pmem,sector) => void*
- * We do not require that sector be page aligned.
- * The return value will point to the beginning of the page containing the
- * given sector, not to the sector itself.
- */
-static void *pmem_lookup_pg_addr(struct pmem_device *pmem, sector_t sector)
-{
-	size_t page_offset = sector >> PAGE_SECTORS_SHIFT;
-	size_t offset = page_offset << PAGE_SHIFT;
-
-	BUG_ON(offset >= pmem->size);
-	return pmem->virt_addr + offset;
-}
-
-/* sector must be page aligned */
-static unsigned long pmem_lookup_pfn(struct pmem_device *pmem, sector_t sector)
-{
-	size_t page_offset = sector >> PAGE_SECTORS_SHIFT;
-
-	BUG_ON(sector & (PAGE_SECTORS - 1));
-	return (pmem->phys_addr >> PAGE_SHIFT) + page_offset;
-}
-
-/*
- * sector is not required to be page aligned.
- * n is at most a single page, but could be less.
- */
-static void copy_to_pmem(struct pmem_device *pmem, const void *src,
-			sector_t sector, size_t n)
-{
-	void *dst;
-	unsigned int offset = (sector & (PAGE_SECTORS - 1)) << SECTOR_SHIFT;
-	size_t copy;
-
-	BUG_ON(n > PAGE_SIZE);
-
-	copy = min_t(size_t, n, PAGE_SIZE - offset);
-	dst = pmem_lookup_pg_addr(pmem, sector);
-	memcpy(dst + offset, src, copy);
-
-	if (copy < n) {
-		src += copy;
-		sector += copy >> SECTOR_SHIFT;
-		copy = n - copy;
-		dst = pmem_lookup_pg_addr(pmem, sector);
-		memcpy(dst, src, copy);
-	}
-}
-
-/*
- * sector is not required to be page aligned.
- * n is at most a single page, but could be less.
- */
-static void copy_from_pmem(void *dst, struct pmem_device *pmem,
-			  sector_t sector, size_t n)
-{
-	void *src;
-	unsigned int offset = (sector & (PAGE_SECTORS - 1)) << SECTOR_SHIFT;
-	size_t copy;
-
-	BUG_ON(n > PAGE_SIZE);
-
-	copy = min_t(size_t, n, PAGE_SIZE - offset);
-	src = pmem_lookup_pg_addr(pmem, sector);
-
-	memcpy(dst, src + offset, copy);
-
-	if (copy < n) {
-		dst += copy;
-		sector += copy >> SECTOR_SHIFT;
-		copy = n - copy;
-		src = pmem_lookup_pg_addr(pmem, sector);
-		memcpy(dst, src, copy);
-	}
-}
-
 static void pmem_do_bvec(struct pmem_device *pmem, struct page *page,
 			unsigned int len, unsigned int off, int rw,
 			sector_t sector)
 {
 	void *mem = kmap_atomic(page);
+	size_t pmem_off = sector << 9;
 
 	if (rw == READ) {
-		copy_from_pmem(mem + off, pmem, sector, len);
+		memcpy(mem + off, pmem->virt_addr + pmem_off, len);
 		flush_dcache_page(page);
 	} else {
 		/*
@@ -136,7 +60,7 @@ static void pmem_do_bvec(struct pmem_device *pmem, struct page *page,
 		 * NVDIMMs are actually durable before returning.
 		 */
 		flush_dcache_page(page);
-		copy_to_pmem(pmem, mem + off, sector, len);
+		memcpy(pmem->virt_addr + pmem_off, mem + off, len);
 	}
 
 	kunmap_atomic(mem);
@@ -152,25 +76,32 @@ static void pmem_make_request(struct request_queue *q, struct bio *bio)
 	struct bvec_iter iter;
 	int err = 0;
 
-	sector = bio->bi_iter.bi_sector;
 	if (bio_end_sector(bio) > get_capacity(bdev->bd_disk)) {
 		err = -EIO;
 		goto out;
 	}
 
-	BUG_ON(bio->bi_rw & REQ_DISCARD);
+	if (WARN_ON(bio->bi_rw & REQ_DISCARD)) {
+		err = -EINVAL;
+		goto out;
+	}
 
 	rw = bio_rw(bio);
 	if (rw == READA)
 		rw = READ;
 
+	sector = bio->bi_iter.bi_sector;
 	bio_for_each_segment(bvec, bio, iter) {
-		unsigned int len = bvec.bv_len;
-
-		BUG_ON(len > PAGE_SIZE);
-		pmem_do_bvec(pmem, bvec.bv_page, len,
-			    bvec.bv_offset, rw, sector);
-		sector += len >> SECTOR_SHIFT;
+		/* NOTE: There is a legend saying that bv_len might be
+		 * bigger than PAGE_SIZE in the case that bv_page points to
+		 * a physical contiguous PFN set. But for us it is fine because
+		 * it means the Kernel virtual mapping is also contiguous. And
+		 * on the pmem side we are always contiguous both virtual and
+		 * physical
+		 */
+		pmem_do_bvec(pmem, bvec.bv_page, bvec.bv_len, bvec.bv_offset,
+			     rw, sector);
+		sector += bvec.bv_len >> 9;
 	}
 
 out:
@@ -191,14 +122,15 @@ static long pmem_direct_access(struct block_device *bdev, sector_t sector,
 			      void **kaddr, unsigned long *pfn, long size)
 {
 	struct pmem_device *pmem = bdev->bd_disk->private_data;
+	size_t offset = sector << 9;
 
 	if (!pmem)
 		return -ENODEV;
 
-	*kaddr = pmem_lookup_pg_addr(pmem, sector);
-	*pfn = pmem_lookup_pfn(pmem, sector);
+	*kaddr = pmem->virt_addr + offset;
+	*pfn = (pmem->phys_addr + offset) >> PAGE_SHIFT;
 
-	return pmem->size - (sector * 512);
+	return pmem->size - offset;
 }
 
 static const struct block_device_operations pmem_fops = {
-- 
1.9.3