block: use an xarray for disk->part_tbl

Now that no fast path lookups in the partition table are left, there is
no point in micro-optimizing the data structure for it.  Just use a bog
standard xarray.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 6 insertions, 25 deletions

diff --git a/block/partitions/core.c b/block/partitions/core.c
index 168d5906077c..b1cdf88f96e2 100644
--- a/block/partitions/core.c
+++ b/block/partitions/core.c
@@ -287,13 +287,7 @@ struct device_type part_type = {
  */
 void delete_partition(struct block_device *part)
 {
-	struct gendisk *disk = part->bd_disk;
-	struct disk_part_tbl *ptbl =
-		rcu_dereference_protected(disk->part_tbl, 1);
-
-	rcu_assign_pointer(ptbl->part[part->bd_partno], NULL);
-	rcu_assign_pointer(ptbl->last_lookup, NULL);
-
+	xa_erase(&part->bd_disk->part_tbl, part->bd_partno);
 	kobject_put(part->bd_holder_dir);
 	device_del(&part->bd_device);
 
@@ -325,7 +319,6 @@ static struct block_device *add_partition(struct gendisk *disk, int partno,
 	struct device *ddev = disk_to_dev(disk);
 	struct device *pdev;
 	struct block_device *bdev;
-	struct disk_part_tbl *ptbl;
 	const char *dname;
 	int err;
 
@@ -347,12 +340,7 @@ static struct block_device *add_partition(struct gendisk *disk, int partno,
 		break;
 	}
 
-	err = disk_expand_part_tbl(disk, partno);
-	if (err)
-		return ERR_PTR(err);
-	ptbl = rcu_dereference_protected(disk->part_tbl, 1);
-
-	if (ptbl->part[partno])
+	if (xa_load(&disk->part_tbl, partno))
 		return ERR_PTR(-EBUSY);
 
 	bdev = bdev_alloc(disk, partno);
@@ -405,8 +393,10 @@ static struct block_device *add_partition(struct gendisk *disk, int partno,
 	}
 
 	/* everything is up and running, commence */
+	err = xa_insert(&disk->part_tbl, partno, bdev, GFP_KERNEL);
+	if (err)
+		goto out_del;
 	bdev_add(bdev, devt);
-	rcu_assign_pointer(ptbl->part[partno], bdev);
 
 	/* suppress uevent if the disk suppresses it */
 	if (!dev_get_uevent_suppress(ddev))
@@ -612,7 +602,7 @@ static bool blk_add_partition(struct gendisk *disk, struct block_device *bdev,
 int blk_add_partitions(struct gendisk *disk, struct block_device *bdev)
 {
 	struct parsed_partitions *state;
-	int ret = -EAGAIN, p, highest;
+	int ret = -EAGAIN, p;
 
 	if (!disk_part_scan_enabled(disk))
 		return 0;
@@ -660,15 +650,6 @@ int blk_add_partitions(struct gendisk *disk, struct block_device *bdev)
 	/* tell userspace that the media / partition table may have changed */
 	kobject_uevent(&disk_to_dev(disk)->kobj, KOBJ_CHANGE);
 
-	/*
-	 * Detect the highest partition number and preallocate disk->part_tbl.
-	 * This is an optimization and not strictly necessary.
-	 */
-	for (p = 1, highest = 0; p < state->limit; p++)
-		if (state->parts[p].size)
-			highest = p;
-	disk_expand_part_tbl(disk, highest);
-
 	for (p = 1; p < state->limit; p++)
 		if (!blk_add_partition(disk, bdev, state, p))
 			goto out_free_state;