Re: [PATCH] erofs: support for mounting a single block device with multiple devices

[Gao Xiang <hsiangkao@linux.alibaba.com>]

Hi Jia,

On 2023/3/1 15:04, Jia Zhu wrote:
> In order to support mounting multi-layer container image as a block
> device, add single block device with multiple devices feature for EROFS.

In order to support mounting multi-blob container image as a single
flattened block device, add flattened block device feature for EROFS.

> 
> In this mode, all meta/data contents will be mapped into one block address.
> User could directly mount the block device by EROFS.
> 
> Signed-off-by: Jia Zhu <zhujia.zj@bytedance.com>
> Reviewed-by: Xin Yin <yinxin.x@bytedance.com>
> ---
>   fs/erofs/data.c  | 8 ++++++--
>   fs/erofs/super.c | 5 +++++
>   2 files changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/erofs/data.c b/fs/erofs/data.c
> index e16545849ea7..870b1f7fe1d4 100644
> --- a/fs/erofs/data.c
> +++ b/fs/erofs/data.c
> @@ -195,9 +195,9 @@ 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;
> +	bool flatdev = !!sb->s_bdev;

I'd like to land it in sbi and set it in advance?

Also, did you test this patch?

Thanks,
Gao Xiang


>   	int id;
>   
> -	/* primary device by default */
>   	map->m_bdev = sb->s_bdev;
>   	map->m_daxdev = EROFS_SB(sb)->dax_dev;
>   	map->m_dax_part_off = EROFS_SB(sb)->dax_part_off;
> @@ -210,12 +210,16 @@ int erofs_map_dev(struct super_block *sb, struct erofs_map_dev *map)
>   			up_read(&devs->rwsem);
>   			return -ENODEV;
>   		}
> +		if (flatdev) {
> +			map->m_pa += blknr_to_addr(dif->mapped_blkaddr);
> +			map->m_deviceid = 0;
> +		}
>   		map->m_bdev = dif->bdev;
>   		map->m_daxdev = dif->dax_dev;
>   		map->m_dax_part_off = dif->dax_part_off;
>   		map->m_fscache = dif->fscache;
>   		up_read(&devs->rwsem);
> -	} else if (devs->extra_devices) {
> +	} else if (devs->extra_devices && !flatdev) {
>   		down_read(&devs->rwsem);
>   		idr_for_each_entry(&devs->tree, dif, id) {
>   			erofs_off_t startoff, length;
> diff --git a/fs/erofs/super.c b/fs/erofs/super.c
> index 19b1ae79cec4..4f9725b0950c 100644
> --- a/fs/erofs/super.c
> +++ b/fs/erofs/super.c
> @@ -226,6 +226,7 @@ static int erofs_init_device(struct erofs_buf *buf, struct super_block *sb,
>   	struct erofs_fscache *fscache;
>   	struct erofs_deviceslot *dis;
>   	struct block_device *bdev;
> +	bool flatdev = !!sb->s_bdev;
>   	void *ptr;
>   
>   	ptr = erofs_read_metabuf(buf, sb, erofs_blknr(*pos), EROFS_KMAP);
> @@ -248,6 +249,10 @@ static int erofs_init_device(struct erofs_buf *buf, struct super_block *sb,
>   		if (IS_ERR(fscache))
>   			return PTR_ERR(fscache);
>   		dif->fscache = fscache;
> +	} else if (flatdev) {
> +		dif->bdev = sb->s_bdev;
> +		dif->dax_dev = EROFS_SB(sb)->dax_dev;
> +		dif->dax_part_off = sbi->dax_part_off;
>   	} else {
>   		bdev = blkdev_get_by_path(dif->path, FMODE_READ | FMODE_EXCL,
>   					  sb->s_type);