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SubjectRe: [PATCH] erofs: support for mounting a single block device with multiple devices
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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);

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