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Date:   Tue, 15 Dec 2020 12:51:02 -0800
From:   "Darrick J. Wong" <darrick.wong@...cle.com>
To:     Shiyang Ruan <ruansy.fnst@...fujitsu.com>
Cc:     linux-kernel@...r.kernel.org, linux-xfs@...r.kernel.org,
        linux-nvdimm@...ts.01.org, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org, linux-raid@...r.kernel.org,
        dan.j.williams@...el.com, david@...morbit.com, hch@....de,
        song@...nel.org, rgoldwyn@...e.de, qi.fuli@...itsu.com,
        y-goto@...itsu.com, "Theodore Ts'o" <tytso@....edu>
Subject: Re: [RFC PATCH v3 8/9] md: Implement ->corrupted_range()

On Tue, Dec 15, 2020 at 08:14:13PM +0800, Shiyang Ruan wrote:
> With the support of ->rmap(), it is possible to obtain the superblock on
> a mapped device.
> 
> If a pmem device is used as one target of mapped device, we cannot
> obtain its superblock directly.  With the help of SYSFS, the mapped
> device can be found on the target devices.  So, we iterate the
> bdev->bd_holder_disks to obtain its mapped device.
> 
> Signed-off-by: Shiyang Ruan <ruansy.fnst@...fujitsu.com>
> ---
>  drivers/md/dm.c       | 66 +++++++++++++++++++++++++++++++++++++++++++
>  drivers/nvdimm/pmem.c |  9 ++++--
>  fs/block_dev.c        | 21 ++++++++++++++
>  include/linux/genhd.h |  7 +++++
>  4 files changed, 100 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/md/dm.c b/drivers/md/dm.c
> index 4e0cbfe3f14d..9da1f9322735 100644
> --- a/drivers/md/dm.c
> +++ b/drivers/md/dm.c
> @@ -507,6 +507,71 @@ static int dm_blk_report_zones(struct gendisk *disk, sector_t sector,
>  #define dm_blk_report_zones		NULL
>  #endif /* CONFIG_BLK_DEV_ZONED */
>  
> +struct dm_blk_corrupt {
> +	struct block_device *bdev;
> +	sector_t offset;
> +};
> +
> +static int dm_blk_corrupt_fn(struct dm_target *ti, struct dm_dev *dev,
> +				sector_t start, sector_t len, void *data)
> +{
> +	struct dm_blk_corrupt *bc = data;
> +
> +	return bc->bdev == (void *)dev->bdev &&
> +			(start <= bc->offset && bc->offset < start + len);
> +}
> +
> +static int dm_blk_corrupted_range(struct gendisk *disk,
> +				  struct block_device *target_bdev,
> +				  loff_t target_offset, size_t len, void *data)
> +{
> +	struct mapped_device *md = disk->private_data;
> +	struct block_device *md_bdev = md->bdev;
> +	struct dm_table *map;
> +	struct dm_target *ti;
> +	struct super_block *sb;
> +	int srcu_idx, i, rc = 0;
> +	bool found = false;
> +	sector_t disk_sec, target_sec = to_sector(target_offset);
> +
> +	map = dm_get_live_table(md, &srcu_idx);
> +	if (!map)
> +		return -ENODEV;
> +
> +	for (i = 0; i < dm_table_get_num_targets(map); i++) {
> +		ti = dm_table_get_target(map, i);
> +		if (ti->type->iterate_devices && ti->type->rmap) {
> +			struct dm_blk_corrupt bc = {target_bdev, target_sec};
> +
> +			found = ti->type->iterate_devices(ti, dm_blk_corrupt_fn, &bc);
> +			if (!found)
> +				continue;
> +			disk_sec = ti->type->rmap(ti, target_sec);

What happens if the dm device has multiple reverse mappings because the
physical storage is being shared at multiple LBAs?  (e.g. a
deduplication target)

> +			break;
> +		}
> +	}
> +
> +	if (!found) {
> +		rc = -ENODEV;
> +		goto out;
> +	}
> +
> +	sb = get_super(md_bdev);
> +	if (!sb) {
> +		rc = bd_disk_holder_corrupted_range(md_bdev, to_bytes(disk_sec), len, data);
> +		goto out;
> +	} else if (sb->s_op->corrupted_range) {
> +		loff_t off = to_bytes(disk_sec - get_start_sect(md_bdev));
> +
> +		rc = sb->s_op->corrupted_range(sb, md_bdev, off, len, data);

This "call bd_disk_holder_corrupted_range or sb->s_op->corrupted_range"
logic appears twice; should it be refactored into a common helper?

Or, should the superblock dispatch part move to
bd_disk_holder_corrupted_range?

> +	}
> +	drop_super(sb);
> +
> +out:
> +	dm_put_live_table(md, srcu_idx);
> +	return rc;
> +}
> +
>  static int dm_prepare_ioctl(struct mapped_device *md, int *srcu_idx,
>  			    struct block_device **bdev)
>  {
> @@ -3084,6 +3149,7 @@ static const struct block_device_operations dm_blk_dops = {
>  	.getgeo = dm_blk_getgeo,
>  	.report_zones = dm_blk_report_zones,
>  	.pr_ops = &dm_pr_ops,
> +	.corrupted_range = dm_blk_corrupted_range,
>  	.owner = THIS_MODULE
>  };
>  
> diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c
> index 4688bff19c20..e8cfaf860149 100644
> --- a/drivers/nvdimm/pmem.c
> +++ b/drivers/nvdimm/pmem.c
> @@ -267,11 +267,14 @@ static int pmem_corrupted_range(struct gendisk *disk, struct block_device *bdev,
>  
>  	bdev_offset = (disk_sector - get_start_sect(bdev)) << SECTOR_SHIFT;
>  	sb = get_super(bdev);
> -	if (sb && sb->s_op->corrupted_range) {
> +	if (!sb) {
> +		rc = bd_disk_holder_corrupted_range(bdev, bdev_offset, len, data);
> +		goto out;
> +	} else if (sb->s_op->corrupted_range)
>  		rc = sb->s_op->corrupted_range(sb, bdev, bdev_offset, len, data);
> -		drop_super(sb);

This is out of scope for this patch(set) but do you think that the scsi
disk driver should intercept media errors from sense data and call
->corrupted_range too?  ISTR Ted muttering that one of his employers had
a patchset to do more with sense data than the upstream kernel currently
does...

> -	}
> +	drop_super(sb);
>  
> +out:
>  	bdput(bdev);
>  	return rc;
>  }
> diff --git a/fs/block_dev.c b/fs/block_dev.c
> index 9e84b1928b94..d3e6bddb8041 100644
> --- a/fs/block_dev.c
> +++ b/fs/block_dev.c
> @@ -1171,6 +1171,27 @@ struct bd_holder_disk {
>  	int			refcnt;
>  };
>  
> +int bd_disk_holder_corrupted_range(struct block_device *bdev, loff_t off, size_t len, void *data)
> +{
> +	struct bd_holder_disk *holder;
> +	struct gendisk *disk;
> +	int rc = 0;
> +
> +	if (list_empty(&(bdev->bd_holder_disks)))
> +		return -ENODEV;
> +
> +	list_for_each_entry(holder, &bdev->bd_holder_disks, list) {
> +		disk = holder->disk;
> +		if (disk->fops->corrupted_range) {
> +			rc = disk->fops->corrupted_range(disk, bdev, off, len, data);
> +			if (rc != -ENODEV)
> +				break;
> +		}
> +	}
> +	return rc;
> +}
> +EXPORT_SYMBOL_GPL(bd_disk_holder_corrupted_range);
> +
>  static struct bd_holder_disk *bd_find_holder_disk(struct block_device *bdev,
>  						  struct gendisk *disk)
>  {
> diff --git a/include/linux/genhd.h b/include/linux/genhd.h
> index ed06209008b8..fba247b852fa 100644
> --- a/include/linux/genhd.h
> +++ b/include/linux/genhd.h
> @@ -382,9 +382,16 @@ int blkdev_ioctl(struct block_device *, fmode_t, unsigned, unsigned long);
>  long compat_blkdev_ioctl(struct file *, unsigned, unsigned long);
>  
>  #ifdef CONFIG_SYSFS
> +int bd_disk_holder_corrupted_range(struct block_device *bdev, loff_t off,
> +				   size_t len, void *data);
>  int bd_link_disk_holder(struct block_device *bdev, struct gendisk *disk);
>  void bd_unlink_disk_holder(struct block_device *bdev, struct gendisk *disk);
>  #else
> +int bd_disk_holder_corrupted_range(struct block_device *bdev, loff_t off,
> +				   size_t len, void *data)
> +{
> +	return 0;
> +}
>  static inline int bd_link_disk_holder(struct block_device *bdev,
>  				      struct gendisk *disk)
>  {
> -- 
> 2.29.2
> 
> 
> 

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