[PATCH v2] erofs-utils: mkfs: support flatdev for multi-blob images

[Gao Xiang]

On 2023/9/15 16:16, Jingbo Xu wrote:
> Since kernel commit 8b465fecc35a ("erofs: support flattened block device
> for multi-blob images"), the flatdev feature has been introduced to
> support mounting multi-blobs container image as a single block device.
> 
> To enable this feature, the mapped_blkaddr of each device slot needs to
> be set properly to the offset of the device in the flat address space.
> 
> The kernel side requires a non-empty device tag to mount an image in
> flatdev mode.  The uuid of the source image is used as the corresponding
> device tag in rebuild mode.
> 
> Signed-off-by: Jingbo Xu <jefflexu at linux.alibaba.com>
> ---
> v2: drop "-Eflatdev" option; always set mapped_blkaddr in device slot
> ---
>   include/erofs/internal.h |  1 +
>   lib/blobchunk.c          |  8 ++++++--
>   lib/super.c              |  1 +
>   mkfs/main.c              | 17 +++++++++++++----
>   4 files changed, 21 insertions(+), 6 deletions(-)
> 
> diff --git a/include/erofs/internal.h b/include/erofs/internal.h
> index 19b912b..616cd3a 100644
> --- a/include/erofs/internal.h
> +++ b/include/erofs/internal.h
> @@ -54,6 +54,7 @@ extern struct erofs_sb_info sbi;
>   struct erofs_buffer_head;
>   
>   struct erofs_device_info {
> +	u8 tag[64];
>   	u32 blocks;
>   	u32 mapped_blkaddr;
>   };
> diff --git a/lib/blobchunk.c b/lib/blobchunk.c
> index aca616e..a599f3a 100644
> --- a/lib/blobchunk.c
> +++ b/lib/blobchunk.c
> @@ -410,20 +410,24 @@ int erofs_mkfs_dump_blobs(struct erofs_sb_info *sbi)
>   	}
>   
>   	if (sbi->extra_devices) {
> -		unsigned int i;
> +		unsigned int i, ret;
> +		erofs_blk_t nblocks;
>   
> +		nblocks = erofs_mapbh(NULL);
>   		pos_out = erofs_btell(bh_devt, false);
>   		i = 0;
>   		do {
>   			struct erofs_deviceslot dis = {
> +				.mapped_blkaddr = cpu_to_le32(nblocks),
>   				.blocks = cpu_to_le32(sbi->devs[i].blocks),
>   			};
> -			int ret;
>   
> +			memcpy(dis.tag, sbi->devs[i].tag, sizeof(dis.tag));
>   			ret = dev_write(sbi, &dis, pos_out, sizeof(dis));
>   			if (ret)
>   				return ret;
>   			pos_out += sizeof(dis);
> +			nblocks += sbi->devs[i].blocks;
>   		} while (++i < sbi->extra_devices);
>   		bh_devt->op = &erofs_drop_directly_bhops;
>   		erofs_bdrop(bh_devt, false);
> diff --git a/lib/super.c b/lib/super.c
> index ce97278..f952f7e 100644
> --- a/lib/super.c
> +++ b/lib/super.c
> @@ -65,6 +65,7 @@ static int erofs_init_devices(struct erofs_sb_info *sbi,
>   
>   		sbi->devs[i].mapped_blkaddr = le32_to_cpu(dis.mapped_blkaddr);
>   		sbi->devs[i].blocks = le32_to_cpu(dis.blocks);
> +		memcpy(sbi->devs[i].tag, dis.tag, sizeof(dis.tag));
>   		sbi->total_blocks += sbi->devs[i].blocks;
>   		pos += EROFS_DEVT_SLOT_SIZE;
>   	}
> diff --git a/mkfs/main.c b/mkfs/main.c
> index 4fa2d92..9327b6f 100644
> --- a/mkfs/main.c
> +++ b/mkfs/main.c
> @@ -765,8 +765,15 @@ static void erofs_mkfs_default_options(void)
>   	sbi.feature_compat = EROFS_FEATURE_COMPAT_SB_CHKSUM |
>   			     EROFS_FEATURE_COMPAT_MTIME;
>   
> -	/* generate a default uuid first */
> -	erofs_uuid_generate(sbi.uuid);
> +	/*
> +	 * Generate a default uuid first.  In rebuild mode the uuid of the
> +	 * source image is used as the device slot's tag.  The kernel will
> +	 * identify the tag as empty and fail the mount if its first byte is
> +	 * zero.  Apply this constraint to uuid to work around it.
> +	 */
> +	do {
> +		erofs_uuid_generate(sbi.uuid);
> +	} while (!sbi.uuid[0]);

I don't think we need this, since uuid need to be parsed to string.

>   }
>   
>   /* https://reproducible-builds.org/specs/source-date-epoch/ for more details */
> @@ -822,7 +829,7 @@ static int erofs_rebuild_load_trees(struct erofs_inode *root)
>   	struct erofs_sb_info *src;
>   	unsigned int extra_devices = 0;
>   	erofs_blk_t nblocks;
> -	int ret;
> +	int ret, idx;
>   
>   	list_for_each_entry(src, &rebuild_src_list, list) {
>   		ret = erofs_rebuild_load_tree(root, src);
> @@ -854,7 +861,9 @@ static int erofs_rebuild_load_trees(struct erofs_inode *root)
>   		else
>   			nblocks = src->primarydevice_blocks;
>   		DBG_BUGON(src->dev < 1);
> -		sbi.devs[src->dev - 1].blocks = nblocks;
> +		idx = src->dev - 1;
> +		sbi.devs[idx].blocks = nblocks;
> +		memcpy(sbi.devs[idx].tag, src->uuid, sizeof(src->uuid));

Should we use string conversion instead? Should we use uuid only
if sbi.devs[idx].tag is empty?

Thanks,
Gao Xiang