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On 2019/6/10 23:06, Gao Xiang wrote:
> There are some backward incompatible optimizations pending
> for months, mainly due to on-disk format expensions.
>
> However, we should ensure that it cannot be mounted with
> old kernels. Otherwise, it will causes unexpected behaviors.
>
> Fixes: ba2b77a82022 ("staging: erofs: add super block operations")
> Cc: <stable@xxxxxxxxxxxxxxx> # 4.19+
> Signed-off-by: Gao Xiang <gaoxiang25@xxxxxxxxxx>
> ---
> drivers/staging/erofs/erofs_fs.h | 11 +++++++++--
> drivers/staging/erofs/super.c | 8 ++++++++
> 2 files changed, 17 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/staging/erofs/erofs_fs.h b/drivers/staging/erofs/erofs_fs.h
> index fa52898df006..531821757845 100644
> --- a/drivers/staging/erofs/erofs_fs.h
> +++ b/drivers/staging/erofs/erofs_fs.h
> @@ -17,10 +17,16 @@
> #define EROFS_SUPER_MAGIC_V1 0xE0F5E1E2
> #define EROFS_SUPER_OFFSET 1024
>
> +/*
> + * Any bits that aren't in EROFS_ALL_REQUIREMENTS should be
> + * incompatible with this kernel version.
> + */
> +#define EROFS_ALL_REQUIREMENTS 0
> +
> struct erofs_super_block {
> /* 0 */__le32 magic; /* in the little endian */
> /* 4 */__le32 checksum; /* crc32c(super_block) */
> -/* 8 */__le32 features;
> +/* 8 */__le32 features; /* extra features for the image */
> /* 12 */__u8 blkszbits; /* support block_size == PAGE_SIZE only */
> /* 13 */__u8 reserved;
>
> @@ -34,8 +40,9 @@ struct erofs_super_block {
> /* 44 */__le32 xattr_blkaddr;
> /* 48 */__u8 uuid[16]; /* 128-bit uuid for volume */
> /* 64 */__u8 volume_name[16]; /* volume name */
> +/* 80 */__le32 requirements; /* all mandatory minimum requirements */
>
> -/* 80 */__u8 reserved2[48]; /* 128 bytes */
> +/* 84 */__u8 reserved2[44]; /* 128 bytes */
> } __packed;
>
> /*
> diff --git a/drivers/staging/erofs/super.c b/drivers/staging/erofs/super.c
> index f580d4ef77a1..815e5825db59 100644
> --- a/drivers/staging/erofs/super.c
> +++ b/drivers/staging/erofs/super.c
> @@ -104,6 +104,14 @@ static int superblock_read(struct super_block *sb)
> goto out;
> }
>
> + /* check if the kernel meets all mandatory requirements */
> + if (le32_to_cpu(layout->requirements) & (~EROFS_ALL_REQUIREMENTS)) {
> + errln("too old to meet minimum requirements: %x supported: %x",
> + le32_to_cpu(layout->requirements),
> + EROFS_ALL_REQUIREMENTS);
> + goto out;
> + }
> +
> sbi->blocks = le32_to_cpu(layout->blocks);
> sbi->meta_blkaddr = le32_to_cpu(layout->meta_blkaddr);
> #ifdef CONFIG_EROFS_FS_XATTR
>
