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

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Message-ID: <538f3643-ca29-f2a7-c077-8039ab137039@huawei.com>
Date:   Tue, 11 Jun 2019 09:47:59 +0800
From:   Chao Yu <yuchao0@...wei.com>
To:     Gao Xiang <gaoxiang25@...wei.com>
CC:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        <devel@...verdev.osuosl.org>, LKML <linux-kernel@...r.kernel.org>,
        <linux-erofs@...ts.ozlabs.org>, Chao Yu <chao@...nel.org>,
        Miao Xie <miaoxie@...wei.com>, <weidu.du@...wei.com>,
        Fang Wei <fangwei1@...wei.com>, <stable@...r.kernel.org>
Subject: Re: [PATCH 1/2] staging: erofs: add requirements field in superblock

On 2019/6/11 9:43, Gao Xiang wrote:
> 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@...r.kernel.org> # 4.19+
>>> Signed-off-by: Gao Xiang <gaoxiang25@...wei.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?

Xiang, I misunderstood meaning of comments, please ignore it, sorry. :)

Thanks,

> 
>>
>>>  } __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
>>>
> .
>