Re: [PATCH 1/2] staging: erofs: add requirements field in superblock

[Gao Xiang <gaoxiang25@huawei.com>]

Hi Chao,

On 2019/6/11 9:37, Chao Yu wrote:
> On 2019/6/10 17:36, 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@vger.kernel.org> # 4.19+
>> Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>
>> ---
>>  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 */
> 
> Xiang,
> 
> It needs to update the comment behind reserved2, it's locating at 132 bytes.

I don't get the point... the whole struct is totally 128bytes I think?

> 
>>  } __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",
> 
> It will be better to give a suggestion to user to upgrade kernel version to
> match the image with new layout, otherwise it's just a little confused about
> above printed message.

OK, I will refine the printed message :)

Thanks,
Gao Xiang

> 
> Thanks,
> 
>> +		      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
>>