Re: [PATCH-v2] erofs-utils:code for calculating crc checksum of erofs blocks.

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

Hi Pratik,

Some nitpick comments... Let me know if you have other thoughts

On Mon, Oct 14, 2019 at 08:29:43PM +0530, Pratik Shinde wrote:
> Added code for calculating crc of erofs blocks (4K size).for now it calculates
> checksum of first block. but can modified to calculate crc for any no. of blocks
> 
> modified patch based on review comments.
> 
> Signed-off-by: Pratik Shinde <pratikshinde320@gmail.com>
> ---
>  include/erofs/internal.h |  1 +
>  include/erofs/io.h       |  8 +++++
>  lib/io.c                 | 27 +++++++++++++++++
>  mkfs/main.c              | 76 ++++++++++++++++++++++++++++++++++++++++++++++++
>  4 files changed, 112 insertions(+)
> 
> diff --git a/include/erofs/internal.h b/include/erofs/internal.h
> index 5384946..53335bc 100644
> --- a/include/erofs/internal.h
> +++ b/include/erofs/internal.h
> @@ -55,6 +55,7 @@ struct erofs_sb_info {
>  	u32 feature_incompat;
>  	u64 build_time;
>  	u32 build_time_nsec;
> +	u32 feature;
>  };
>  
>  /* global sbi */
> diff --git a/include/erofs/io.h b/include/erofs/io.h
> index 9775047..e0ca8d9 100644
> --- a/include/erofs/io.h
> +++ b/include/erofs/io.h
> @@ -19,6 +19,7 @@
>  int dev_open(const char *devname);
>  void dev_close(void);
>  int dev_write(const void *buf, u64 offset, size_t len);
> +int dev_read(void *buf, u64 offset, size_t len);
>  int dev_fillzero(u64 offset, size_t len, bool padding);
>  int dev_fsync(void);
>  int dev_resize(erofs_blk_t nblocks);
> @@ -31,5 +32,12 @@ static inline int blk_write(const void *buf, erofs_blk_t blkaddr,
>  			 blknr_to_addr(nblocks));
>  }
>  
> +static inline int blk_read(void *buf, erofs_blk_t start,
> +			    u32 nblocks)
> +{
> +	return dev_read(buf, blknr_to_addr(start),
> +			 blknr_to_addr(nblocks));
> +}
> +
>  #endif
>  
> diff --git a/lib/io.c b/lib/io.c
> index 7f5f94d..52f9424 100644
> --- a/lib/io.c
> +++ b/lib/io.c
> @@ -207,3 +207,30 @@ int dev_resize(unsigned int blocks)
>  	return dev_fillzero(st.st_size, length, true);
>  }
>  
> +int dev_read(void *buf, u64 offset, size_t len)
> +{
> +	int ret;
> +
> +	if (cfg.c_dry_run)
> +		return 0;
> +
> +	if (!buf) {
> +		erofs_err("buf is NULL");
> +		return -EINVAL;
> +	}
> +	if (offset >= erofs_devsz || len > erofs_devsz ||
> +	    offset > erofs_devsz - len) {
> +		erofs_err("read posion[%" PRIu64 ", %zd] is too large beyond"
> +			  "the end of device(%" PRIu64 ").",
> +			  offset, len, erofs_devsz);
> +		return -EINVAL;
> +	}
> +
> +	ret = pread64(erofs_devfd, buf, len, (off64_t)offset);
> +	if (ret != (int)len) {
> +		erofs_err("Failed to read data from device - %s:[%" PRIu64 ", %zd].",
> +			  erofs_devname, offset, len);
> +		return -errno;
> +	}
> +	return 0;
> +}
> diff --git a/mkfs/main.c b/mkfs/main.c
> index 91a018f..baaf02a 100644
> --- a/mkfs/main.c
> +++ b/mkfs/main.c
> @@ -22,6 +22,10 @@
>  
>  #define EROFS_SUPER_END (EROFS_SUPER_OFFSET + sizeof(struct erofs_super_block))
>  
> +/* number of blocks for calculating checksum */
> +#define EROFS_CKSUM_BLOCKS	1
> +#define EROFS_FEATURE_SB_CHKSUM	0x0001

How about Moving EROFS_FEATURE_SB_CHKSUM to erofs_fs.h since it's
an on-disk definition,

> +
>  static void usage(void)
>  {
>  	fprintf(stderr, "usage: [options] FILE DIRECTORY\n\n");
> @@ -85,6 +89,10 @@ static int parse_extended_opts(const char *opts)
>  				return -EINVAL;
>  			cfg.c_force_inodeversion = FORCE_INODE_EXTENDED;
>  		}
> +
> +		if (MATCH_EXTENTED_OPT("nocrc", token, keylen)) {
> +			sbi.feature &= ~EROFS_FEATURE_SB_CHKSUM;
> +		}
>  	}
>  	return 0;
>  }
> @@ -180,6 +188,7 @@ int erofs_mkfs_update_super_block(struct erofs_buffer_head *bh,
>  		.meta_blkaddr  = sbi.meta_blkaddr,
>  		.xattr_blkaddr = 0,
>  		.feature_incompat = cpu_to_le32(sbi.feature_incompat),
> +		.checksum = 0
>  	};
>  	const unsigned int sb_blksize =
>  		round_up(EROFS_SUPER_END, EROFS_BLKSIZ);
> @@ -202,6 +211,70 @@ int erofs_mkfs_update_super_block(struct erofs_buffer_head *bh,
>  	return 0;
>  }
>  
> +#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);
> +		}
> +	}
> +	return crc;
> +}
> +
> +/* calculate checksum for first n blocks */
> +u32 erofs_calc_blk_checksum(erofs_blk_t nblks, u32 *crc)
> +{
> +	char *buf;
> +	int err = 0;
> +
> +	buf = malloc(nblks * EROFS_BLKSIZ);
> +	err = blk_read(buf, 0, nblks);
> +	if (err) {
> +		erofs_err("Failed to calculate erofs checksum - %s",
> +			  erofs_strerror(err));
> +		return err;
> +	}
> +	*crc = crc32c(0, (const unsigned char *)buf, nblks * EROFS_BLKSIZ);
> +	free(buf);
> +	return 0;
> +}
> +
> +void erofs_write_checksum()

How about naming write_sb_checksum?
My idea is that this is a checksum in super block (rather than
a checksum only for super block [0th block])

Let me know if you have another thought...

> +{
> +	struct erofs_super_block *sb;
> +	char buf[EROFS_BLKSIZ];
> +	int ret = 0;
> +	u32 crc;
> +
> +	ret = erofs_calc_blk_checksum(EROFS_CKSUM_BLOCKS, &crc);
> +	if (ret) {
> +		return;
> +	}
> +	ret = blk_read(buf, 0, 1);
> +	if (ret) {
> +		erofs_err("error reading super-block structure");
> +		return;
> +	}
> +
> +	sb = (struct erofs_super_block *)((u8 *)buf + EROFS_SUPER_OFFSET);
> +	if (le32_to_cpu(sb->magic) != EROFS_SUPER_MAGIC_V1) {
> +		erofs_err("not an erofs image");

As the previous comments, I am little care about these print messages
since users will only see this and "error reading super-block structure"
"not an erofs image" makes confused for them... (They don't know what
the internal process is doing)

BTW, it looks good to me as a whole... Do you have some time on
kernel side as well? :)

Thanks,
Gao Xiang

> +		return;
> +	}
> +	sb->checksum = cpu_to_le32(crc);
> +	ret = blk_write(buf, 0, 1);
> +	if (ret) {
> +		erofs_err("error writing 0th block to disk - %s",
> +			  erofs_strerror(ret));
> +		return;
> +	}
> +}
> +
>  int main(int argc, char **argv)
>  {
>  	int err = 0;
> @@ -217,6 +290,7 @@ int main(int argc, char **argv)
>  
>  	cfg.c_legacy_compress = false;
>  	sbi.feature_incompat = EROFS_FEATURE_INCOMPAT_LZ4_0PADDING;
> +	sbi.feature = EROFS_FEATURE_SB_CHKSUM;
>  
>  	err = mkfs_parse_options_cfg(argc, argv);
>  	if (err) {
> @@ -301,6 +375,8 @@ int main(int argc, char **argv)
>  		err = -EIO;
>  	else
>  		err = dev_resize(nblocks);
> +	if (sbi.feature & EROFS_FEATURE_SB_CHKSUM)
> +		erofs_write_checksum();
>  exit:
>  	z_erofs_compress_exit();
>  	dev_close();
> -- 
> 2.9.3
>