zram: make zram_bio_discard more self-contained

Derive the index and offset variables inside the function, and complete
the bio directly in preparation for cleaning up the I/O path.

Link: https://lkml.kernel.org/r/20230411171459.567614-4-hch@lst.deSigned-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

drivers/block/zram/zram_drv.c

@@ -1890,15 +1890,12 @@ static ssize_t recompress_store(struct device *dev,
 }
 #endif
 
-/*
- * zram_bio_discard - handler on discard request
- * @index: physical block index in PAGE_SIZE units
- * @offset: byte offset within physical block
- */
-static void zram_bio_discard(struct zram *zram, u32 index,
-			     int offset, struct bio *bio)
+static void zram_bio_discard(struct zram *zram, struct bio *bio)
 {
 	size_t n = bio->bi_iter.bi_size;
+	u32 index = bio->bi_iter.bi_sector >> SECTORS_PER_PAGE_SHIFT;
+	u32 offset = (bio->bi_iter.bi_sector & (SECTORS_PER_PAGE - 1)) <<
+			SECTOR_SHIFT;
 
 	/*
 	 * zram manages data in physical block size units. Because logical block
@@ -1926,6 +1923,8 @@ static void zram_bio_discard(struct zram *zram, u32 index,
 		index++;
 		n -= PAGE_SIZE;
 	}
+
+	bio_endio(bio);
 }
 
 /*
@@ -1974,8 +1973,7 @@ static void __zram_make_request(struct zram *zram, struct bio *bio)
 	switch (bio_op(bio)) {
 	case REQ_OP_DISCARD:
 	case REQ_OP_WRITE_ZEROES:
-		zram_bio_discard(zram, index, offset, bio);
-		bio_endio(bio);
+		zram_bio_discard(zram, bio);
 		return;
 	default:
 		break;