Re: [PATCH] erofs-utils: code for superblock checksum calculation.

[Gao Xiang via Linux-erofs <linux-erofs@lists.ozlabs.org>]

Hi Pratik,

On Sat, Aug 24, 2019 at 06:08:03PM +0530, Pratik Shinde wrote:
> Adding code for superblock checksum calculation.
> 
> incorporated the changes suggested in previous patch.
> 
> Signed-off-by: Pratik Shinde <pratikshinde320@gmail.com>

Thanks for your v2 patch.

Actually, I have some concern about the length of checksum,
sizeof(struct erofs_super_block) could be changed in the
later version, it's bad for EROFS future scalablity.

And I tend not to add another on-disk field to record
the size of erofs_super_block as well, because the old
Linux kernel cannot handle more about the new size,
so it has little use except for checksum calculation.

Few hours ago, I discussed with Chao about this concern,
I think this feature can be changed to do multiple-block
checksum at the mount time, e.g:
 - for small images, we can check the whole image once
   at the mount time;
 - for the large image, we can check the superblock
   at the mount time, the rest can be handled by
   block-based verification layer.

But we agreed that don't add this for this round
since it's quite a new feature.

All in all, it's a new feature since we are addressing moving
out of staging for this round. I tend to postpone this feature
for now. I understand that you are very interested in EROFS.
Considering EROFS current staging status, it's not such a place
to add new features at all! I have marked your patch down and
I will work with you later. Hope to get your understanding...

Thanks,
Gao Xiang

> ---
>  include/erofs/config.h |  1 +
>  include/erofs_fs.h     | 10 ++++++++
>  mkfs/main.c            | 64 +++++++++++++++++++++++++++++++++++++++++++++++++-
>  3 files changed, 74 insertions(+), 1 deletion(-)
> 
> diff --git a/include/erofs/config.h b/include/erofs/config.h
> index 05fe6b2..40cd466 100644
> --- a/include/erofs/config.h
> +++ b/include/erofs/config.h
> @@ -22,6 +22,7 @@ struct erofs_configure {
>  	char *c_src_path;
>  	char *c_compr_alg_master;
>  	int c_compr_level_master;
> +	int c_feature_flags;
>  };
>  
>  extern struct erofs_configure cfg;
> diff --git a/include/erofs_fs.h b/include/erofs_fs.h
> index 601b477..9ac2635 100644
> --- a/include/erofs_fs.h
> +++ b/include/erofs_fs.h
> @@ -20,6 +20,16 @@
>  #define EROFS_REQUIREMENT_LZ4_0PADDING	0x00000001
>  #define EROFS_ALL_REQUIREMENTS		EROFS_REQUIREMENT_LZ4_0PADDING
>  
> +/*
> + * feature definations.
> + */
> +#define EROFS_DEFAULT_FEATURES		EROFS_FEATURE_SB_CHKSUM
> +#define EROFS_FEATURE_SB_CHKSUM		0x0001
> +
> +
> +#define EROFS_HAS_COMPAT_FEATURE(super,mask)	\
> +	( le32_to_cpu((super)->features) & (mask) )
> +
>  struct erofs_super_block {
>  /*  0 */__le32 magic;           /* in the little endian */
>  /*  4 */__le32 checksum;        /* crc32c(super_block) */
> diff --git a/mkfs/main.c b/mkfs/main.c
> index f127fe1..355fd2c 100644
> --- a/mkfs/main.c
> +++ b/mkfs/main.c
> @@ -31,6 +31,45 @@ static void usage(void)
>  	fprintf(stderr, " -EX[,...] X=extended options\n");
>  }
>  
> +#define CRCPOLY	0x82F63B78
> +static inline u32 crc32c(u32 seed, unsigned char const *in, size_t len)
> +{
> +	int i;
> +	u32 crc = seed;
> +
> +	while (len--) {
> +		crc ^= *in++;
> +		for (i = 0; i < 8; i++) {
> +			crc = (crc >> 1) ^ ((crc & 1) ? CRCPOLY : 0);
> +		}
> +	}
> +	erofs_dump("calculated crc: 0x%x\n", crc);
> +	return crc;
> +}
> +
> +char *feature_opts[] = {
> +	"nosbcrc", NULL
> +};
> +#define O_SB_CKSUM	0
> +
> +static int parse_feature_subopts(char *opts)
> +{
> +	char *arg;
> +
> +	cfg.c_feature_flags = EROFS_DEFAULT_FEATURES;
> +	while (*opts != '\0') {
> +		switch(getsubopt(&opts, feature_opts, &arg)) {
> +		case O_SB_CKSUM:
> +			cfg.c_feature_flags |= (~EROFS_FEATURE_SB_CHKSUM);
> +			break;
> +		default:
> +			erofs_err("incorrect suboption");
> +			return -EINVAL;
> +		}
> +	}
> +	return 0;
> +}
> +
>  static int parse_extended_opts(const char *opts)
>  {
>  #define MATCH_EXTENTED_OPT(opt, token, keylen) \
> @@ -79,7 +118,8 @@ static int mkfs_parse_options_cfg(int argc, char *argv[])
>  {
>  	int opt, i;
>  
> -	while ((opt = getopt(argc, argv, "d:z:E:")) != -1) {
> +	cfg.c_feature_flags = EROFS_DEFAULT_FEATURES;
> +	while ((opt = getopt(argc, argv, "d:z:E:o:")) != -1) {
>  		switch (opt) {
>  		case 'z':
>  			if (!optarg) {
> @@ -113,6 +153,12 @@ static int mkfs_parse_options_cfg(int argc, char *argv[])
>  				return opt;
>  			break;
>  
> +		case 'O':
> +			opt = parse_feature_subopts(optarg);
> +			if (opt)
> +				return opt;
> +			break;
> +
>  		default: /* '?' */
>  			return -EINVAL;
>  		}
> @@ -144,6 +190,15 @@ static int mkfs_parse_options_cfg(int argc, char *argv[])
>  	return 0;
>  }
>  
> +u32 erofs_superblock_checksum(struct erofs_super_block *sb)
> +{
> +	u32 crc;
> +	crc = crc32c(~0, (const unsigned char *)sb,
> +		    sizeof(struct erofs_super_block));
> +	erofs_dump("superblock checksum: 0x%x\n", crc);
> +	return crc;
> +}
> +
>  int erofs_mkfs_update_super_block(struct erofs_buffer_head *bh,
>  				  erofs_nid_t root_nid)
>  {
> @@ -155,6 +210,7 @@ int erofs_mkfs_update_super_block(struct erofs_buffer_head *bh,
>  		.meta_blkaddr  = sbi.meta_blkaddr,
>  		.xattr_blkaddr = 0,
>  		.requirements = cpu_to_le32(sbi.requirements),
> +		.features = cpu_to_le32(cfg.c_feature_flags),
>  	};
>  	const unsigned int sb_blksize =
>  		round_up(EROFS_SUPER_END, EROFS_BLKSIZ);
> @@ -169,6 +225,12 @@ int erofs_mkfs_update_super_block(struct erofs_buffer_head *bh,
>  	sb.blocks       = cpu_to_le32(erofs_mapbh(NULL, true));
>  	sb.root_nid     = cpu_to_le16(root_nid);
>  
> +	if (EROFS_HAS_COMPAT_FEATURE(&sb, EROFS_FEATURE_SB_CHKSUM)) {
> +		sb.checksum = 0;
> +		u32 crc = erofs_superblock_checksum(&sb);
> +		sb.checksum = cpu_to_le32(crc);
> +	}
> +
>  	buf = calloc(sb_blksize, 1);
>  	if (!buf) {
>  		erofs_err("Failed to allocate memory for sb: %s",
> -- 
> 2.9.3
>