partition scan

Linux 6.18.37 LTS: block/genhd.c
Linux 6.18.37 LTS: block/partitions/core.c
Linux 6.18.37 LTS: include/linux/blkdev.h

static int blk_add_partitions(struct gendisk *disk)
{
	struct parsed_partitions *state;
	int ret = -EAGAIN, p;

	if (!disk_has_partscan(disk))
		return 0;

	state = check_partition(disk);
	if (!state)
		return 0;
	if (IS_ERR(state)) {
		/*
		 * I/O error reading the partition table.  If we tried to read
		 * beyond EOD, retry after unlocking the native capacity.
		 */
		if (PTR_ERR(state) == -ENOSPC) {
			printk(KERN_WARNING "%s: partition table beyond EOD, ",
			       disk->disk_name);
			if (disk_unlock_native_capacity(disk))
				return -EAGAIN;
		}
		return -EIO;
	}

	/*
	 * Partitions are not supported on host managed zoned block devices.
	 */
	if (bdev_is_zoned(disk->part0)) {
		pr_warn("%s: ignoring partition table on host managed zoned block device\n",
			disk->disk_name);
		ret = 0;
		goto out_free_state;
	}

	/*
	 * If we read beyond EOD, try unlocking native capacity even if the
	 * partition table was successfully read as we could be missing some
	 * partitions.
	 */
	if (state->access_beyond_eod) {
		printk(KERN_WARNING
		       "%s: partition table partially beyond EOD, ",
		       disk->disk_name);
		if (disk_unlock_native_capacity(disk))
			goto out_free_state;
	}

	/* tell userspace that the media / partition table may have changed */
	kobject_uevent(&disk_to_dev(disk)->kobj, KOBJ_CHANGE);

	for (p = 1; p < state->limit; p++)
		if (!blk_add_partition(disk, state, p))
			goto out_free_state;

	ret = 0;
out_free_state:
	free_partitions(state);
	return ret;
}

int bdev_disk_changed(struct gendisk *disk, bool invalidate)
{
	struct block_device *part;
	unsigned long idx;
	int ret = 0;

	lockdep_assert_held(&disk->open_mutex);

	if (!disk_live(disk))
		return -ENXIO;

rescan:
	if (disk->open_partitions)
		return -EBUSY;
	sync_blockdev(disk->part0);
	invalidate_bdev(disk->part0);

	xa_for_each_start(&disk->part_tbl, idx, part, 1) {
		/*
		 * Remove the block device from the inode hash, so that
		 * it cannot be looked up any more even when openers
		 * still hold references.
		 */
		bdev_unhash(part);

		/*
		 * If @disk->open_partitions isn't elevated but there's
		 * still an active holder of that block device things
		 * are broken.
		 */
		WARN_ON_ONCE(atomic_read(&part->bd_openers));
		invalidate_bdev(part);
		drop_partition(part);
	}
	clear_bit(GD_NEED_PART_SCAN, &disk->state);

	/*
	 * Historically we only set the capacity to zero for devices that
	 * support partitions (independ of actually having partitions created).
	 * Doing that is rather inconsistent, but changing it broke legacy
	 * udisks polling for legacy ide-cdrom devices.  Use the crude check
	 * below to get the sane behavior for most device while not breaking
	 * userspace for this particular setup.
	 */
	if (invalidate) {
		if (!(disk->flags & GENHD_FL_NO_PART) ||
		    !(disk->flags & GENHD_FL_REMOVABLE))
			set_capacity(disk, 0);
	}

	if (get_capacity(disk)) {
		ret = blk_add_partitions(disk);
		if (ret == -EAGAIN)
			goto rescan;
	} else if (invalidate) {
		/*
		 * Tell userspace that the media / partition table may have
		 * changed.
		 */
		kobject_uevent(&disk_to_dev(disk)->kobj, KOBJ_CHANGE);
	}

	return ret;
}
/*
 * Only exported for loop and dasd for historic reasons.  Don't use in new
 * code!
 */
EXPORT_SYMBOL_GPL(bdev_disk_changed);