Re: [RFC ONLY 6/8] btrfs: add code to read raid extent

[Josef Bacik <josef@toxicpanda.com>]

On Mon, May 16, 2022 at 07:31:41AM -0700, Johannes Thumshirn wrote:
> Add boilerplate code to lookup the physical address from the
> raid-stripe-tree when a read on an RAID volume formatted with the
> raid-stripe-tree was attempted.
> 
> Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
> ---
>  fs/btrfs/raid-stripe-tree.c | 68 +++++++++++++++++++++++++++++++++++++
>  fs/btrfs/raid-stripe-tree.h |  3 ++
>  fs/btrfs/volumes.c          | 23 +++++++++++--
>  3 files changed, 91 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/btrfs/raid-stripe-tree.c b/fs/btrfs/raid-stripe-tree.c
> index 370ea68fe343..ecc8205be760 100644
> --- a/fs/btrfs/raid-stripe-tree.c
> +++ b/fs/btrfs/raid-stripe-tree.c
> @@ -1,10 +1,78 @@
>  // SPDX-License-Identifier: GPL-2.0
>  
> +#include <linux/btrfs_tree.h>
> +
>  #include "ctree.h"
>  #include "transaction.h"
>  #include "disk-io.h"
>  #include "raid-stripe-tree.h"
>  #include "volumes.h"
> +#include "misc.h"
> +
> +int btrfs_get_raid_extent_offset(struct btrfs_fs_info *fs_info,
> +				 u64 logical, u64 length, u64 map_type,
> +				 u64 devid, u64 *physical)
> +{
> +	struct btrfs_root *stripe_root = fs_info->stripe_root;
> +	struct btrfs_dp_stripe *raid_stripe;
> +	struct btrfs_key stripe_key;
> +	struct btrfs_key found_key;
> +	struct btrfs_path *path;
> +	struct extent_buffer *leaf;
> +	u64 offset;
> +	u64 found_logical, found_length;
> +	int num_stripes;
> +	int slot;
> +	int ret;
> +	int i;
> +
> +	stripe_key.objectid = logical;
> +	stripe_key.type = BTRFS_RAID_STRIPE_KEY;
> +	stripe_key.offset = length;
> +
> +	path = btrfs_alloc_path();
> +	if (!path)
> +		return -ENOMEM;
> +
> +	num_stripes = btrfs_bg_type_to_factor(map_type);
> +
> +	ret = btrfs_search_slot_for_read(stripe_root, &stripe_key, path, 0, 0);
> +	if (ret < 0) {
> +		goto out;
> +	}
> +
> +	if (ret == 1)
> +		ret = 0;
> +
> +	while (1) {
> +		leaf = path->nodes[0];
> +		slot = path->slots[0];
> +
> +		btrfs_item_key_to_cpu(leaf, &found_key, slot);
> +		found_logical = found_key.objectid;
> +		found_length = found_key.offset;
> +
> +		if (!in_range(logical, found_logical, found_length))
> +		    goto next;
> +		offset = logical - found_logical;
> +
> +		raid_stripe = btrfs_item_ptr(leaf, slot, struct btrfs_dp_stripe);
> +		for (i = 0; i < num_stripes; i++) {
> +			if (btrfs_stripe_extent_devid_nr(leaf, raid_stripe, i) != devid)
> +				continue;
> +			*physical = btrfs_stripe_extent_offset_nr(leaf, raid_stripe, i) + offset;
> +			goto out;
> +		}
> +next:
> +		ret = btrfs_next_item(stripe_root, path);
> +		if (ret)

This will leak 1 if we don't find a stripe, probably should do EUCLEAN if we
don't have a raid stripe for this?  Thanks,

Josef