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Date:   Thu, 7 Oct 2021 14:42:21 +0800
From:   Liu Bo <bo.liu@linux.alibaba.com>
To:     Gao Xiang <hsiangkao@linux.alibaba.com>
Cc:     linux-erofs@lists.ozlabs.org, Chao Yu <chao@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Peng Tao <tao.peng@linux.alibaba.com>,
        Yan Song <imeoer@linux.alibaba.com>,
        Changwei Ge <chge@linux.alibaba.com>,
        Liu Jiang <gerry@linux.alibaba.com>,
        Joseph Qi <joseph.qi@linux.alibaba.com>
Subject: Re: [PATCH v3 2/2] erofs: add multiple device support
Message-ID: <20211007064220.GB84859@rsjd01523.et2sqa>
Reply-To: bo.liu@linux.alibaba.com
References: <20211006194453.130447-1-hsiangkao@linux.alibaba.com>
 <20211006194453.130447-2-hsiangkao@linux.alibaba.com>
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User-Agent: Mutt/1.5.21 (2010-09-15)
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On Thu, Oct 07, 2021 at 03:44:53AM +0800, Gao Xiang wrote:
> In order to support multi-layer container images, add multiple
> device feature to EROFS. Two ways are available to use for now:
> 
>  - Devices can be mapped into 32-bit global block address space;
>  - Device ID can be specified with the chunk indexes format.
> 
> Note that it assumes no extent would cross device boundary and mkfs
> should take care of it seriously.
> 
> In the future, a dedicated device manager could be introduced then
> so extra devices can be automatically scanned by uuid as well.
>

Reviewed-by: Liu Bo <bo.liu@linux.alibaba.com>

thanks,
liubo

> Cc: Liu Bo <bo.liu@linux.alibaba.com>
> Cc: Chao Yu <chao@kernel.org>
> Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
> ---
>  Documentation/filesystems/erofs.rst |  12 ++-
>  fs/erofs/data.c                     |  73 ++++++++++---
>  fs/erofs/erofs_fs.h                 |  20 +++-
>  fs/erofs/internal.h                 |  35 ++++++-
>  fs/erofs/super.c                    | 155 ++++++++++++++++++++++++++--
>  fs/erofs/zdata.c                    |  20 +++-
>  6 files changed, 279 insertions(+), 36 deletions(-)
> 
> diff --git a/Documentation/filesystems/erofs.rst b/Documentation/filesystems/erofs.rst
> index b97579b7d8fb..01df283c7d04 100644
> --- a/Documentation/filesystems/erofs.rst
> +++ b/Documentation/filesystems/erofs.rst
> @@ -19,9 +19,10 @@ It is designed as a better filesystem solution for the following scenarios:
>     immutable and bit-for-bit identical to the official golden image for
>     their releases due to security and other considerations and
>  
> - - hope to save some extra storage space with guaranteed end-to-end performance
> -   by using reduced metadata and transparent file compression, especially
> -   for those embedded devices with limited memory (ex, smartphone);
> + - hope to minimize extra storage space with guaranteed end-to-end performance
> +   by using compact layout, transparent file compression and direct access,
> +   especially for those embedded devices with limited memory and high-density
> +   hosts with numerous containers;
>  
>  Here is the main features of EROFS:
>  
> @@ -51,7 +52,9 @@ Here is the main features of EROFS:
>   - Support POSIX.1e ACLs by using xattrs;
>  
>   - Support transparent data compression as an option:
> -   LZ4 algorithm with the fixed-sized output compression for high performance.
> +   LZ4 algorithm with the fixed-sized output compression for high performance;
> +
> + - Multiple device support for multi-layer container images.
>  
>  The following git tree provides the file system user-space tools under
>  development (ex, formatting tool mkfs.erofs):
> @@ -87,6 +90,7 @@ cache_strategy=%s      Select a strategy for cached decompression from now on:
>  dax={always,never}     Use direct access (no page cache).  See
>                         Documentation/filesystems/dax.rst.
>  dax                    A legacy option which is an alias for ``dax=always``.
> +device=%s              Specify a path to an extra device to be used together.
>  ===================    =========================================================
>  
>  On-disk details
> diff --git a/fs/erofs/data.c b/fs/erofs/data.c
> index 9db829715652..808234d9190c 100644
> --- a/fs/erofs/data.c
> +++ b/fs/erofs/data.c
> @@ -89,6 +89,7 @@ static int erofs_map_blocks(struct inode *inode,
>  	erofs_off_t pos;
>  	int err = 0;
>  
> +	map->m_deviceid = 0;
>  	if (map->m_la >= inode->i_size) {
>  		/* leave out-of-bound access unmapped */
>  		map->m_flags = 0;
> @@ -135,14 +136,8 @@ static int erofs_map_blocks(struct inode *inode,
>  		map->m_flags = 0;
>  		break;
>  	default:
> -		/* only one device is supported for now */
> -		if (idx->device_id) {
> -			erofs_err(sb, "invalid device id %u @ %llu for nid %llu",
> -				  le16_to_cpu(idx->device_id),
> -				  chunknr, vi->nid);
> -			err = -EFSCORRUPTED;
> -			goto out_unlock;
> -		}
> +		map->m_deviceid = le16_to_cpu(idx->device_id) &
> +			EROFS_SB(sb)->device_id_mask;
>  		map->m_pa = blknr_to_addr(le32_to_cpu(idx->blkaddr));
>  		map->m_flags = EROFS_MAP_MAPPED;
>  		break;
> @@ -155,11 +150,55 @@ static int erofs_map_blocks(struct inode *inode,
>  	return err;
>  }
>  
> +int erofs_map_dev(struct super_block *sb, struct erofs_map_dev *map)
> +{
> +	struct erofs_dev_context *devs = EROFS_SB(sb)->devs;
> +	struct erofs_device_info *dif;
> +	int id;
> +
> +	/* primary device by default */
> +	map->m_bdev = sb->s_bdev;
> +	map->m_daxdev = EROFS_SB(sb)->dax_dev;
> +
> +	if (map->m_deviceid) {
> +		down_read(&devs->rwsem);
> +		dif = idr_find(&devs->tree, map->m_deviceid - 1);
> +		if (!dif) {
> +			up_read(&devs->rwsem);
> +			return -ENODEV;
> +		}
> +		map->m_bdev = dif->bdev;
> +		map->m_daxdev = dif->dax_dev;
> +		up_read(&devs->rwsem);
> +	} else if (devs->extra_devices) {
> +		down_read(&devs->rwsem);
> +		idr_for_each_entry(&devs->tree, dif, id) {
> +			erofs_off_t startoff, length;
> +
> +			if (!dif->mapped_blkaddr)
> +				continue;
> +			startoff = blknr_to_addr(dif->mapped_blkaddr);
> +			length = blknr_to_addr(dif->blocks);
> +
> +			if (map->m_pa >= startoff &&
> +			    map->m_pa < startoff + length) {
> +				map->m_pa -= startoff;
> +				map->m_bdev = dif->bdev;
> +				map->m_daxdev = dif->dax_dev;
> +				break;
> +			}
> +		}
> +		up_read(&devs->rwsem);
> +	}
> +	return 0;
> +}
> +
>  static int erofs_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
>  		unsigned int flags, struct iomap *iomap, struct iomap *srcmap)
>  {
>  	int ret;
>  	struct erofs_map_blocks map;
> +	struct erofs_map_dev mdev;
>  
>  	map.m_la = offset;
>  	map.m_llen = length;
> @@ -168,8 +207,16 @@ static int erofs_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
>  	if (ret < 0)
>  		return ret;
>  
> -	iomap->bdev = inode->i_sb->s_bdev;
> -	iomap->dax_dev = EROFS_I_SB(inode)->dax_dev;
> +	mdev = (struct erofs_map_dev) {
> +		.m_deviceid = map.m_deviceid,
> +		.m_pa = map.m_pa,
> +	};
> +	ret = erofs_map_dev(inode->i_sb, &mdev);
> +	if (ret)
> +		return ret;
> +
> +	iomap->bdev = mdev.m_bdev;
> +	iomap->dax_dev = mdev.m_daxdev;
>  	iomap->offset = map.m_la;
>  	iomap->length = map.m_llen;
>  	iomap->flags = 0;
> @@ -188,15 +235,15 @@ static int erofs_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
>  
>  		iomap->type = IOMAP_INLINE;
>  		ipage = erofs_get_meta_page(inode->i_sb,
> -					    erofs_blknr(map.m_pa));
> +					    erofs_blknr(mdev.m_pa));
>  		if (IS_ERR(ipage))
>  			return PTR_ERR(ipage);
>  		iomap->inline_data = page_address(ipage) +
> -					erofs_blkoff(map.m_pa);
> +					erofs_blkoff(mdev.m_pa);
>  		iomap->private = ipage;
>  	} else {
>  		iomap->type = IOMAP_MAPPED;
> -		iomap->addr = map.m_pa;
> +		iomap->addr = mdev.m_pa;
>  	}
>  	return 0;
>  }
> diff --git a/fs/erofs/erofs_fs.h b/fs/erofs/erofs_fs.h
> index b0b23f41abc3..c2f1c2453a55 100644
> --- a/fs/erofs/erofs_fs.h
> +++ b/fs/erofs/erofs_fs.h
> @@ -21,14 +21,27 @@
>  #define EROFS_FEATURE_INCOMPAT_COMPR_CFGS	0x00000002
>  #define EROFS_FEATURE_INCOMPAT_BIG_PCLUSTER	0x00000002
>  #define EROFS_FEATURE_INCOMPAT_CHUNKED_FILE	0x00000004
> +#define EROFS_FEATURE_INCOMPAT_DEVICE_TABLE	0x00000008
>  #define EROFS_ALL_FEATURE_INCOMPAT		\
>  	(EROFS_FEATURE_INCOMPAT_LZ4_0PADDING | \
>  	 EROFS_FEATURE_INCOMPAT_COMPR_CFGS | \
>  	 EROFS_FEATURE_INCOMPAT_BIG_PCLUSTER | \
> -	 EROFS_FEATURE_INCOMPAT_CHUNKED_FILE)
> +	 EROFS_FEATURE_INCOMPAT_CHUNKED_FILE | \
> +	 EROFS_FEATURE_INCOMPAT_DEVICE_TABLE)
>  
>  #define EROFS_SB_EXTSLOT_SIZE	16
>  
> +struct erofs_deviceslot {
> +	union {
> +		u8 uuid[16];		/* used for device manager later */
> +		u8 userdata[64];	/* digest(sha256), etc. */
> +	} u;
> +	__le32 blocks;
> +	__le32 mapped_blkaddr;
> +	u8 reserved[56];
> +};
> +#define EROFS_DEVT_SLOT_SIZE	sizeof(struct erofs_deviceslot)
> +
>  /* erofs on-disk super block (currently 128 bytes) */
>  struct erofs_super_block {
>  	__le32 magic;           /* file system magic number */
> @@ -54,7 +67,9 @@ struct erofs_super_block {
>  		/* customized sliding window size instead of 64k by default */
>  		__le16 lz4_max_distance;
>  	} __packed u1;
> -	__u8 reserved2[42];
> +	__le16 extra_devices;	/* # of devices besides the primary device */
> +	__le16 devt_slotoff;	/* startoff = devt_slotoff * devt_slotsize */
> +	__u8 reserved2[38];
>  };
>  
>  /*
> @@ -384,6 +399,7 @@ static inline void erofs_check_ondisk_layout_definitions(void)
>  	/* keep in sync between 2 index structures for better extendibility */
>  	BUILD_BUG_ON(sizeof(struct erofs_inode_chunk_index) !=
>  		     sizeof(struct z_erofs_vle_decompressed_index));
> +	BUILD_BUG_ON(sizeof(struct erofs_deviceslot) != 128);
>  
>  	BUILD_BUG_ON(BIT(Z_EROFS_VLE_DI_CLUSTER_TYPE_BITS) <
>  		     Z_EROFS_VLE_CLUSTER_TYPE_MAX - 1);
> diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h
> index b1b9d1b5cb66..34f0933fd0c0 100644
> --- a/fs/erofs/internal.h
> +++ b/fs/erofs/internal.h
> @@ -47,6 +47,15 @@ typedef u64 erofs_off_t;
>  /* data type for filesystem-wide blocks number */
>  typedef u32 erofs_blk_t;
>  
> +struct erofs_device_info {
> +	char *path;
> +	struct block_device *bdev;
> +	struct dax_device *dax_dev;
> +
> +	u32 blocks;
> +	u32 mapped_blkaddr;
> +};
> +
>  struct erofs_mount_opts {
>  #ifdef CONFIG_EROFS_FS_ZIP
>  	/* current strategy of how to use managed cache */
> @@ -60,8 +69,16 @@ struct erofs_mount_opts {
>  	unsigned int mount_opt;
>  };
>  
> +struct erofs_dev_context {
> +	struct idr tree;
> +	struct rw_semaphore rwsem;
> +
> +	unsigned int extra_devices;
> +};
> +
>  struct erofs_fs_context {
>  	struct erofs_mount_opts opt;
> +	struct erofs_dev_context *devs;
>  };
>  
>  /* all filesystem-wide lz4 configurations */
> @@ -74,7 +91,6 @@ struct erofs_sb_lz4_info {
>  
>  struct erofs_sb_info {
>  	struct erofs_mount_opts opt;	/* options */
> -
>  #ifdef CONFIG_EROFS_FS_ZIP
>  	/* list for all registered superblocks, mainly for shrinker */
>  	struct list_head list;
> @@ -91,12 +107,16 @@ struct erofs_sb_info {
>  
>  	struct erofs_sb_lz4_info lz4;
>  #endif	/* CONFIG_EROFS_FS_ZIP */
> +	struct erofs_dev_context *devs;
>  	struct dax_device *dax_dev;
> -	u32 blocks;
> +	u64 total_blocks;
> +	u32 primarydevice_blocks;
> +
>  	u32 meta_blkaddr;
>  #ifdef CONFIG_EROFS_FS_XATTR
>  	u32 xattr_blkaddr;
>  #endif
> +	u16 device_id_mask;
>  
>  	/* inode slot unit size in bit shift */
>  	unsigned char islotbits;
> @@ -241,6 +261,7 @@ static inline bool erofs_sb_has_##name(struct erofs_sb_info *sbi) \
>  EROFS_FEATURE_FUNCS(lz4_0padding, incompat, INCOMPAT_LZ4_0PADDING)
>  EROFS_FEATURE_FUNCS(compr_cfgs, incompat, INCOMPAT_COMPR_CFGS)
>  EROFS_FEATURE_FUNCS(big_pcluster, incompat, INCOMPAT_BIG_PCLUSTER)
> +EROFS_FEATURE_FUNCS(device_table, incompat, INCOMPAT_DEVICE_TABLE)
>  EROFS_FEATURE_FUNCS(sb_chksum, compat, COMPAT_SB_CHKSUM)
>  
>  /* atomic flag definitions */
> @@ -359,6 +380,7 @@ struct erofs_map_blocks {
>  	erofs_off_t m_pa, m_la;
>  	u64 m_plen, m_llen;
>  
> +	unsigned int m_deviceid;
>  	unsigned int m_flags;
>  
>  	struct page *mpage;
> @@ -390,9 +412,18 @@ static inline int z_erofs_map_blocks_iter(struct inode *inode,
>  }
>  #endif	/* !CONFIG_EROFS_FS_ZIP */
>  
> +struct erofs_map_dev {
> +	struct block_device *m_bdev;
> +	struct dax_device *m_daxdev;
> +
> +	erofs_off_t m_pa;
> +	unsigned int m_deviceid;
> +};
> +
>  /* data.c */
>  extern const struct file_operations erofs_file_fops;
>  struct page *erofs_get_meta_page(struct super_block *sb, erofs_blk_t blkaddr);
> +int erofs_map_dev(struct super_block *sb, struct erofs_map_dev *dev);
>  int erofs_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
>  		 u64 start, u64 len);
>  
> diff --git a/fs/erofs/super.c b/fs/erofs/super.c
> index 25f6b8b37f28..f4dd20f76862 100644
> --- a/fs/erofs/super.c
> +++ b/fs/erofs/super.c
> @@ -252,6 +252,79 @@ static int erofs_load_compr_cfgs(struct super_block *sb,
>  }
>  #endif
>  
> +static int erofs_init_devices(struct super_block *sb,
> +			      struct erofs_super_block *dsb)
> +{
> +	struct erofs_sb_info *sbi = EROFS_SB(sb);
> +	unsigned int ondisk_extradevs;
> +	erofs_off_t pos;
> +	struct page *page = NULL;
> +	struct erofs_device_info *dif;
> +	struct erofs_deviceslot *dis;
> +	void *ptr;
> +	int id, err = 0;
> +
> +	sbi->total_blocks = sbi->primarydevice_blocks;
> +	if (!erofs_sb_has_device_table(sbi))
> +		ondisk_extradevs = 0;
> +	else
> +		ondisk_extradevs = le16_to_cpu(dsb->extra_devices);
> +
> +	if (ondisk_extradevs != sbi->devs->extra_devices) {
> +		erofs_err(sb, "extra devices don't match (ondisk %u, given %u)",
> +			  ondisk_extradevs, sbi->devs->extra_devices);
> +		return -EINVAL;
> +	}
> +	if (!ondisk_extradevs)
> +		return 0;
> +
> +	sbi->device_id_mask = roundup_pow_of_two(ondisk_extradevs + 1) - 1;
> +	pos = le16_to_cpu(dsb->devt_slotoff) * EROFS_DEVT_SLOT_SIZE;
> +	down_read(&sbi->devs->rwsem);
> +	idr_for_each_entry(&sbi->devs->tree, dif, id) {
> +		erofs_blk_t blk = erofs_blknr(pos);
> +		struct block_device *bdev;
> +
> +		if (!page || page->index != blk) {
> +			if (page) {
> +				kunmap(page);
> +				unlock_page(page);
> +				put_page(page);
> +			}
> +
> +			page = erofs_get_meta_page(sb, blk);
> +			if (IS_ERR(page)) {
> +				up_read(&sbi->devs->rwsem);
> +				return PTR_ERR(page);
> +			}
> +			ptr = kmap(page);
> +		}
> +		dis = ptr + erofs_blkoff(pos);
> +
> +		bdev = blkdev_get_by_path(dif->path,
> +					  FMODE_READ | FMODE_EXCL,
> +					  sb->s_type);
> +		if (IS_ERR(bdev)) {
> +			err = PTR_ERR(bdev);
> +			goto err_out;
> +		}
> +		dif->bdev = bdev;
> +		dif->dax_dev = fs_dax_get_by_bdev(bdev);
> +		dif->blocks = le32_to_cpu(dis->blocks);
> +		dif->mapped_blkaddr = le32_to_cpu(dis->mapped_blkaddr);
> +		sbi->total_blocks += dif->blocks;
> +		pos += sizeof(*dis);
> +	}
> +err_out:
> +	up_read(&sbi->devs->rwsem);
> +	if (page) {
> +		kunmap(page);
> +		unlock_page(page);
> +		put_page(page);
> +	}
> +	return err;
> +}
> +
>  static int erofs_read_superblock(struct super_block *sb)
>  {
>  	struct erofs_sb_info *sbi;
> @@ -303,7 +376,7 @@ static int erofs_read_superblock(struct super_block *sb)
>  			  sbi->sb_size);
>  		goto out;
>  	}
> -	sbi->blocks = le32_to_cpu(dsb->blocks);
> +	sbi->primarydevice_blocks = le32_to_cpu(dsb->blocks);
>  	sbi->meta_blkaddr = le32_to_cpu(dsb->meta_blkaddr);
>  #ifdef CONFIG_EROFS_FS_XATTR
>  	sbi->xattr_blkaddr = le32_to_cpu(dsb->xattr_blkaddr);
> @@ -330,6 +403,11 @@ static int erofs_read_superblock(struct super_block *sb)
>  		ret = erofs_load_compr_cfgs(sb, dsb);
>  	else
>  		ret = z_erofs_load_lz4_config(sb, dsb, NULL, 0);
> +	if (ret < 0)
> +		goto out;
> +
> +	/* handle multiple devices */
> +	ret = erofs_init_devices(sb, dsb);
>  out:
>  	kunmap(page);
>  	put_page(page);
> @@ -358,6 +436,7 @@ enum {
>  	Opt_cache_strategy,
>  	Opt_dax,
>  	Opt_dax_enum,
> +	Opt_device,
>  	Opt_err
>  };
>  
> @@ -381,6 +460,7 @@ static const struct fs_parameter_spec erofs_fs_parameters[] = {
>  		     erofs_param_cache_strategy),
>  	fsparam_flag("dax",             Opt_dax),
>  	fsparam_enum("dax",		Opt_dax_enum, erofs_dax_param_enums),
> +	fsparam_string("device",	Opt_device),
>  	{}
>  };
>  
> @@ -412,9 +492,10 @@ static bool erofs_fc_set_dax_mode(struct fs_context *fc, unsigned int mode)
>  static int erofs_fc_parse_param(struct fs_context *fc,
>  				struct fs_parameter *param)
>  {
> -	struct erofs_fs_context *ctx __maybe_unused = fc->fs_private;
> +	struct erofs_fs_context *ctx = fc->fs_private;
>  	struct fs_parse_result result;
> -	int opt;
> +	struct erofs_device_info *dif;
> +	int opt, ret;
>  
>  	opt = fs_parse(fc, erofs_fs_parameters, param, &result);
>  	if (opt < 0)
> @@ -456,6 +537,25 @@ static int erofs_fc_parse_param(struct fs_context *fc,
>  		if (!erofs_fc_set_dax_mode(fc, result.uint_32))
>  			return -EINVAL;
>  		break;
> +	case Opt_device:
> +		dif = kzalloc(sizeof(*dif), GFP_KERNEL);
> +		if (!dif)
> +			return -ENOMEM;
> +		dif->path = kstrdup(param->string, GFP_KERNEL);
> +		if (!dif->path) {
> +			kfree(dif);
> +			return -ENOMEM;
> +		}
> +		down_write(&ctx->devs->rwsem);
> +		ret = idr_alloc(&ctx->devs->tree, dif, 0, 0, GFP_KERNEL);
> +		up_write(&ctx->devs->rwsem);
> +		if (ret < 0) {
> +			kfree(dif->path);
> +			kfree(dif);
> +			return ret;
> +		}
> +		++ctx->devs->extra_devices;
> +		break;
>  	default:
>  		return -ENOPARAM;
>  	}
> @@ -542,6 +642,9 @@ static int erofs_fc_fill_super(struct super_block *sb, struct fs_context *fc)
>  	sb->s_fs_info = sbi;
>  	sbi->opt = ctx->opt;
>  	sbi->dax_dev = fs_dax_get_by_bdev(sb->s_bdev);
> +	sbi->devs = ctx->devs;
> +	ctx->devs = NULL;
> +
>  	err = erofs_read_superblock(sb);
>  	if (err)
>  		return err;
> @@ -617,9 +720,32 @@ static int erofs_fc_reconfigure(struct fs_context *fc)
>  	return 0;
>  }
>  
> +static int erofs_release_device_info(int id, void *ptr, void *data)
> +{
> +	struct erofs_device_info *dif = ptr;
> +
> +	fs_put_dax(dif->dax_dev);
> +	if (dif->bdev)
> +		blkdev_put(dif->bdev, FMODE_READ | FMODE_EXCL);
> +	kfree(dif->path);
> +	kfree(dif);
> +	return 0;
> +}
> +
> +static void erofs_free_dev_context(struct erofs_dev_context *devs)
> +{
> +	if (!devs)
> +		return;
> +	idr_for_each(&devs->tree, &erofs_release_device_info, NULL);
> +	idr_destroy(&devs->tree);
> +}
> +
>  static void erofs_fc_free(struct fs_context *fc)
>  {
> -	kfree(fc->fs_private);
> +	struct erofs_fs_context *ctx = fc->fs_private;
> +
> +	erofs_free_dev_context(ctx->devs);
> +	kfree(ctx);
>  }
>  
>  static const struct fs_context_operations erofs_context_ops = {
> @@ -631,13 +757,20 @@ static const struct fs_context_operations erofs_context_ops = {
>  
>  static int erofs_init_fs_context(struct fs_context *fc)
>  {
> -	fc->fs_private = kzalloc(sizeof(struct erofs_fs_context), GFP_KERNEL);
> -	if (!fc->fs_private)
> -		return -ENOMEM;
> +	struct erofs_fs_context *ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
>  
> -	/* set default mount options */
> -	erofs_default_options(fc->fs_private);
> +	if (!ctx)
> +		return -ENOMEM;
> +	ctx->devs = kzalloc(sizeof(struct erofs_dev_context), GFP_KERNEL);
> +	if (!ctx->devs) {
> +		kfree(ctx);
> +		return -ENOMEM;
> +	}
> +	fc->fs_private = ctx;
>  
> +	idr_init(&ctx->devs->tree);
> +	init_rwsem(&ctx->devs->rwsem);
> +	erofs_default_options(ctx);
>  	fc->ops = &erofs_context_ops;
>  	return 0;
>  }
> @@ -657,6 +790,8 @@ static void erofs_kill_sb(struct super_block *sb)
>  	sbi = EROFS_SB(sb);
>  	if (!sbi)
>  		return;
> +
> +	erofs_free_dev_context(sbi->devs);
>  	fs_put_dax(sbi->dax_dev);
>  	kfree(sbi);
>  	sb->s_fs_info = NULL;
> @@ -746,7 +881,7 @@ static int erofs_statfs(struct dentry *dentry, struct kstatfs *buf)
>  
>  	buf->f_type = sb->s_magic;
>  	buf->f_bsize = EROFS_BLKSIZ;
> -	buf->f_blocks = sbi->blocks;
> +	buf->f_blocks = sbi->total_blocks;
>  	buf->f_bfree = buf->f_bavail = 0;
>  
>  	buf->f_files = ULLONG_MAX;
> diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
> index e59e22852c78..8c947ed49299 100644
> --- a/fs/erofs/zdata.c
> +++ b/fs/erofs/zdata.c
> @@ -1266,8 +1266,9 @@ static void z_erofs_submit_queue(struct super_block *sb,
>  	struct z_erofs_decompressqueue *q[NR_JOBQUEUES];
>  	void *bi_private;
>  	z_erofs_next_pcluster_t owned_head = f->clt.owned_head;
> -	/* since bio will be NULL, no need to initialize last_index */
> +	/* bio is NULL initially, so no need to initialize last_{index,bdev} */
>  	pgoff_t last_index;
> +	struct block_device *last_bdev;
>  	unsigned int nr_bios = 0;
>  	struct bio *bio = NULL;
>  
> @@ -1279,6 +1280,7 @@ static void z_erofs_submit_queue(struct super_block *sb,
>  	q[JQ_SUBMIT]->head = owned_head;
>  
>  	do {
> +		struct erofs_map_dev mdev;
>  		struct z_erofs_pcluster *pcl;
>  		pgoff_t cur, end;
>  		unsigned int i = 0;
> @@ -1290,7 +1292,13 @@ static void z_erofs_submit_queue(struct super_block *sb,
>  
>  		pcl = container_of(owned_head, struct z_erofs_pcluster, next);
>  
> -		cur = pcl->obj.index;
> +		/* no device id here, thus it will always succeed */
> +		mdev = (struct erofs_map_dev) {
> +			.m_pa = blknr_to_addr(pcl->obj.index),
> +		};
> +		(void)erofs_map_dev(sb, &mdev);
> +
> +		cur = erofs_blknr(mdev.m_pa);
>  		end = cur + pcl->pclusterpages;
>  
>  		/* close the main owned chain at first */
> @@ -1306,7 +1314,8 @@ static void z_erofs_submit_queue(struct super_block *sb,
>  			if (!page)
>  				continue;
>  
> -			if (bio && cur != last_index + 1) {
> +			if (bio && (cur != last_index + 1 ||
> +				    last_bdev != mdev.m_bdev)) {
>  submit_bio_retry:
>  				submit_bio(bio);
>  				bio = NULL;
> @@ -1314,9 +1323,10 @@ static void z_erofs_submit_queue(struct super_block *sb,
>  
>  			if (!bio) {
>  				bio = bio_alloc(GFP_NOIO, BIO_MAX_VECS);
> -
>  				bio->bi_end_io = z_erofs_decompressqueue_endio;
> -				bio_set_dev(bio, sb->s_bdev);
> +
> +				bio_set_dev(bio, mdev.m_bdev);
> +				last_bdev = mdev.m_bdev;
>  				bio->bi_iter.bi_sector = (sector_t)cur <<
>  					LOG_SECTORS_PER_BLOCK;
>  				bio->bi_private = bi_private;
> -- 
> 2.24.4