On Fri, Apr 15, 2022 at 08:36:03PM +0800, Jeffle Xu wrote:
> Until then erofs is exactly blockdev based filesystem.
>
> A new fscache-based mode is going to be introduced for erofs to support
> scenarios where on-demand read semantics is needed, e.g. container
> image distribution. In this case, erofs could be mounted from data blobs
> through fscache.
>
> Add a helper checking which mode erofs works in, and twist the code in
> prep for the following fscache mode.
in preparation for the upcoming fscache mode.
>
> Signed-off-by: Jeffle Xu <jefflexu@xxxxxxxxxxxxxxxxx>
Reviewed-by: Gao Xiang <hsiangkao@xxxxxxxxxxxxxxxxx>
Thanks,
Gao Xiang
> ---
> fs/erofs/internal.h | 5 +++++
> fs/erofs/super.c | 44 +++++++++++++++++++++++++++++---------------
> 2 files changed, 34 insertions(+), 15 deletions(-)
>
> diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h
> index fe9564e5091e..05a97533b1e9 100644
> --- a/fs/erofs/internal.h
> +++ b/fs/erofs/internal.h
> @@ -161,6 +161,11 @@ struct erofs_sb_info {
> #define set_opt(opt, option) ((opt)->mount_opt |= EROFS_MOUNT_##option)
> #define test_opt(opt, option) ((opt)->mount_opt & EROFS_MOUNT_##option)
>
> +static inline bool erofs_is_fscache_mode(struct super_block *sb)
> +{
> + return IS_ENABLED(CONFIG_EROFS_FS_ONDEMAND) && !sb->s_bdev;
> +}
> +
> enum {
> EROFS_ZIP_CACHE_DISABLED,
> EROFS_ZIP_CACHE_READAHEAD,
> diff --git a/fs/erofs/super.c b/fs/erofs/super.c
> index 0c4b41130c2f..724d5ff0d78c 100644
> --- a/fs/erofs/super.c
> +++ b/fs/erofs/super.c
> @@ -259,15 +259,19 @@ static int erofs_init_devices(struct super_block *sb,
> }
> 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);
> - break;
> + if (!erofs_is_fscache_mode(sb)) {
> + bdev = blkdev_get_by_path(dif->path,
> + FMODE_READ | FMODE_EXCL,
> + sb->s_type);
> + if (IS_ERR(bdev)) {
> + err = PTR_ERR(bdev);
> + break;
> + }
> + dif->bdev = bdev;
> + dif->dax_dev = fs_dax_get_by_bdev(bdev,
> + &dif->dax_part_off);
> }
> - dif->bdev = bdev;
> - dif->dax_dev = fs_dax_get_by_bdev(bdev, &dif->dax_part_off);
> +
> dif->blocks = le32_to_cpu(dis->blocks);
> dif->mapped_blkaddr = le32_to_cpu(dis->mapped_blkaddr);
> sbi->total_blocks += dif->blocks;
> @@ -586,21 +590,28 @@ static int erofs_fc_fill_super(struct super_block *sb, struct fs_context *fc)
>
> sb->s_magic = EROFS_SUPER_MAGIC;
>
> - if (!sb_set_blocksize(sb, EROFS_BLKSIZ)) {
> - erofs_err(sb, "failed to set erofs blksize");
> - return -EINVAL;
> - }
> -
> sbi = kzalloc(sizeof(*sbi), GFP_KERNEL);
> if (!sbi)
> return -ENOMEM;
>
> sb->s_fs_info = sbi;
> sbi->opt = ctx->opt;
> - sbi->dax_dev = fs_dax_get_by_bdev(sb->s_bdev, &sbi->dax_part_off);
> sbi->devs = ctx->devs;
> ctx->devs = NULL;
>
> + if (erofs_is_fscache_mode(sb)) {
> + sb->s_blocksize = EROFS_BLKSIZ;
> + sb->s_blocksize_bits = LOG_BLOCK_SIZE;
> + } else {
> + if (!sb_set_blocksize(sb, EROFS_BLKSIZ)) {
> + erofs_err(sb, "failed to set erofs blksize");
> + return -EINVAL;
> + }
> +
> + sbi->dax_dev = fs_dax_get_by_bdev(sb->s_bdev,
> + &sbi->dax_part_off);
> + }
> +
> err = erofs_read_superblock(sb);
> if (err)
> return err;
> @@ -857,7 +868,10 @@ static int erofs_statfs(struct dentry *dentry, struct kstatfs *buf)
> {
> struct super_block *sb = dentry->d_sb;
> struct erofs_sb_info *sbi = EROFS_SB(sb);
> - u64 id = huge_encode_dev(sb->s_bdev->bd_dev);
> + u64 id = 0;
> +
> + if (!erofs_is_fscache_mode(sb))
> + id = huge_encode_dev(sb->s_bdev->bd_dev);
>
> buf->f_type = sb->s_magic;
> buf->f_bsize = EROFS_BLKSIZ;
> --
> 2.27.0
