[PATCH 1/8] block: split __blkdev_get

Christoph Hellwig
2021-05-25T06:13:18Z

Split __blkdev_get into one helper for the whole device, and one for
opening partitions. This removes the (bounded) recursion when opening
a partition.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
---
fs/block_dev.c | 118 ++++++++++++++++++++++++-------------------------
1 file changed, 57 insertions(+), 61 deletions(-)

diff --git a/fs/block_dev.c b/fs/block_dev.c
index 6cc4d4cfe0c2..2b5073e3c923 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -1290,78 +1290,68 @@ int bdev_disk_changed(struct block_device *bdev, bool invalidate)
*/
EXPORT_SYMBOL_GPL(bdev_disk_changed);

-/*
- * bd_mutex locking:
- *
- * mutex_lock(part->bd_mutex)
- * mutex_lock_nested(whole->bd_mutex, 1)
- */
-static int __blkdev_get(struct block_device *bdev, fmode_t mode)
+static int blkdev_get_whole(struct block_device *bdev, fmode_t mode)
{
struct gendisk *disk = bdev->bd_disk;
int ret = 0;

- if (!(disk->flags & GENHD_FL_UP))
- return -ENXIO;
+ if (disk->fops->open) {
+ ret = disk->fops->open(bdev, mode);
+ if (ret) {
+ /* avoid ghost partitions on a removed medium */
+ if (ret == -ENOMEDIUM &&
+ test_bit(GD_NEED_PART_SCAN, &disk->state))
+ bdev_disk_changed(bdev, true);
+ return ret;
+ }
+ }

if (!bdev->bd_openers) {
- if (!bdev_is_partition(bdev)) {
- ret = 0;
- if (disk->fops->open)
- ret = disk->fops->open(bdev, mode);
+ set_init_blocksize(bdev);
+ if (bdev->bd_bdi == &noop_backing_dev_info)
+ bdev->bd_bdi = bdi_get(disk->queue->backing_dev_info);
+ }
+ if (test_bit(GD_NEED_PART_SCAN, &disk->state))
+ bdev_disk_changed(bdev, false);
+ bdev->bd_openers++;
+ return 0;;
+}

- if (!ret)
- set_init_blocksize(bdev);
+static int blkdev_get_part(struct block_device *part, fmode_t mode)
+{
+ struct gendisk *disk = part->bd_disk;
+ struct block_device *whole;
+ int ret;

- /*
- * If the device is invalidated, rescan partition
- * if open succeeded or failed with -ENOMEDIUM.
- * The latter is necessary to prevent ghost
- * partitions on a removed medium.
- */
- if (test_bit(GD_NEED_PART_SCAN, &disk->state) &&
- (!ret || ret == -ENOMEDIUM))
- bdev_disk_changed(bdev, ret == -ENOMEDIUM);
+ if (part->bd_openers)
+ goto done;

- if (ret)
- return ret;
- } else {
- struct block_device *whole = bdgrab(disk->part0);
-
- mutex_lock_nested(&whole->bd_mutex, 1);
- ret = __blkdev_get(whole, mode);
- if (ret) {
- mutex_unlock(&whole->bd_mutex);
- bdput(whole);
- return ret;
- }
- whole->bd_part_count++;
- mutex_unlock(&whole->bd_mutex);
+ whole = bdgrab(disk->part0);
+ mutex_lock_nested(&whole->bd_mutex, 1);
+ ret = blkdev_get_whole(whole, mode);
+ if (ret) {
+ mutex_unlock(&whole->bd_mutex);
+ goto out_put_whole;
+ }
+ whole->bd_part_count++;
+ mutex_unlock(&whole->bd_mutex);

- if (!bdev_nr_sectors(bdev)) {
- __blkdev_put(whole, mode, 1);
- bdput(whole);
- return -ENXIO;
- }
- set_init_blocksize(bdev);
- }
+ ret = -ENXIO;
+ if (!bdev_nr_sectors(part))
+ goto out_blkdev_put;

- if (bdev->bd_bdi == &noop_backing_dev_info)
- bdev->bd_bdi = bdi_get(disk->queue->backing_dev_info);
- } else {
- if (!bdev_is_partition(bdev)) {
- if (bdev->bd_disk->fops->open)
- ret = bdev->bd_disk->fops->open(bdev, mode);
- /* the same as first opener case, read comment there */
- if (test_bit(GD_NEED_PART_SCAN, &disk->state) &&
- (!ret || ret == -ENOMEDIUM))
- bdev_disk_changed(bdev, ret == -ENOMEDIUM);
- if (ret)
- return ret;
- }
- }
- bdev->bd_openers++;
+ set_init_blocksize(part);
+ if (part->bd_bdi == &noop_backing_dev_info)
+ part->bd_bdi = bdi_get(disk->queue->backing_dev_info);
+done:
+ part->bd_openers++;
return 0;
+
+out_blkdev_put:
+ __blkdev_put(whole, mode, 1);
+out_put_whole:
+ bdput(whole);
+ return ret;
}

struct block_device *blkdev_get_no_open(dev_t dev)
@@ -1448,7 +1438,13 @@ struct block_device *blkdev_get_by_dev(dev_t dev, fmode_t mode, void *holder)
disk_block_events(disk);

mutex_lock(&bdev->bd_mutex);
- ret =__blkdev_get(bdev, mode);
+ ret = -ENXIO;
+ if (!(disk->flags & GENHD_FL_UP))
+ goto abort_claiming;
+ if (bdev_is_partition(bdev))
+ ret = blkdev_get_part(bdev, mode);
+ else
+ ret = blkdev_get_whole(bdev, mode);
if (ret)
goto abort_claiming;
if (mode & FMODE_EXCL) {
--
2.30.2