linux-kernel - Re: [PATCH v3 2/2] erofs: set block size to the on-disk block size

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Date:   Thu, 2 Mar 2023 21:23:46 +0800
From:   Gao Xiang <hsiangkao@...ux.alibaba.com>
To:     Jingbo Xu <jefflexu@...ux.alibaba.com>, xiang@...nel.org,
        chao@...nel.org, huyue2@...lpad.com, linux-erofs@...ts.ozlabs.org
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/2] erofs: set block size to the on-disk block size

Hi Jingbo,

On 2023/2/20 10:50, Jingbo Xu wrote:
> Set the block size to that specified in on-disk superblock.
> 
> Also remove the hard constraint of PAGE_SIZE block size for the
> uncompressed device backend.  This constraint is temporarily remained
> for compressed device and fscache backend, as there is more work needed
> to handle the condition where the block size is not equal to PAGE_SIZE.
> 
> It is worth noting that the on-disk block size is read prior to
> erofs_superblock_csum_verify(), as the read block size is needed in the
> latter.
> 
> Signed-off-by: Jingbo Xu <jefflexu@...ux.alibaba.com>
> ---
>   fs/erofs/erofs_fs.h |  2 +-
>   fs/erofs/inode.c    |  3 ++-
>   fs/erofs/internal.h |  8 --------
>   fs/erofs/super.c    | 42 +++++++++++++++++++++++++++---------------
>   4 files changed, 30 insertions(+), 25 deletions(-)
> 
> diff --git a/fs/erofs/erofs_fs.h b/fs/erofs/erofs_fs.h
> index dbcd24371002..5c7647d68c07 100644
> --- a/fs/erofs/erofs_fs.h
> +++ b/fs/erofs/erofs_fs.h
> @@ -53,7 +53,7 @@ struct erofs_super_block {
>   	__le32 magic;           /* file system magic number */
>   	__le32 checksum;        /* crc32c(super_block) */
>   	__le32 feature_compat;
> -	__u8 blkszbits;         /* support block_size == PAGE_SIZE only */
> +	__u8 blkszbits;         /* filesystem block size */
>   	__u8 sb_extslots;	/* superblock size = 128 + sb_extslots * 16 */
>   
>   	__le16 root_nid;	/* nid of root directory */

Due to we already support < page_size blocks, laterly, we'd consider
refer to tar data blobs (which is 512-byte aligned) for OCI
containers.

So we will have another use case is to use 512-byte block size, but
in that case, dir block size is too small.

So I'd like to add a reserved bit
	__u8 dirblkbits;

for this.

> diff --git a/fs/erofs/inode.c b/fs/erofs/inode.c
> index de26dac4e07e..0e6ff8a98c68 100644
> --- a/fs/erofs/inode.c
> +++ b/fs/erofs/inode.c
> @@ -291,7 +291,8 @@ static int erofs_fill_inode(struct inode *inode)
>   	}
>   
>   	if (erofs_inode_is_data_compressed(vi->datalayout)) {
> -		if (!erofs_is_fscache_mode(inode->i_sb))
> +		if (!erofs_is_fscache_mode(inode->i_sb) &&
> +		    inode->i_sb->s_blocksize_bits == PAGE_SHIFT)
>   			err = z_erofs_fill_inode(inode);
>   		else
>   			err = -EOPNOTSUPP;
> diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h
> index d8019d835405..612543915e9e 100644
> --- a/fs/erofs/internal.h
> +++ b/fs/erofs/internal.h
> @@ -240,14 +240,6 @@ static inline int erofs_wait_on_workgroup_freezed(struct erofs_workgroup *grp)
>   					VAL != EROFS_LOCKED_MAGIC);
>   }
>   
> -/* we strictly follow PAGE_SIZE and no buffer head yet */
> -#define LOG_BLOCK_SIZE		PAGE_SHIFT
> -#define EROFS_BLKSIZ		(1 << LOG_BLOCK_SIZE)
> -
> -#if (EROFS_BLKSIZ % 4096 || !EROFS_BLKSIZ)
> -#error erofs cannot be used in this platform
> -#endif
> -
>   enum erofs_kmap_type {
>   	EROFS_NO_KMAP,		/* don't map the buffer */
>   	EROFS_KMAP,		/* use kmap_local_page() to map the buffer */
> diff --git a/fs/erofs/super.c b/fs/erofs/super.c
> index c97615c96ef8..89011a4ed274 100644
> --- a/fs/erofs/super.c
> +++ b/fs/erofs/super.c
> @@ -349,6 +349,14 @@ static int erofs_read_superblock(struct super_block *sb)
>   		goto out;
>   	}
>   
> +	blkszbits = dsb->blkszbits;
> +	sbi->blkszbits = dsb->blkszbits;
> +	if (blkszbits < 9 || blkszbits > PAGE_SHIFT) {
> +		erofs_err(sb, "blkszbits %u isn't supported on this platform",
> +			  blkszbits);
> +		goto out;
> +	}

Also,
	if (blkszbits != PAGE_SHIFT && dsb->dirblkbits) {
		erofs_err("dirblkbits %u isn't supported", dsb->dirblkbits);
		goto out;
	}

Thanks,
Gao Xiang