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SubjectRe: [PATCH v3 2/2] erofs: set block size to the on-disk block size
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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@linux.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

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