<div dir="ltr"><div>Thanks Chao,</div><div><br></div><div>Initially I was of doing the same, but then I thought changing the position of cheksum field to either start OR end <br></div><div>will be much simpler. <br></div><div>I think I will go with Gao's method. thereby not changing the layout of super-block.</div><div>So just to be clear, I will be writing our own crc32c() function correct ?</div><div><br></div><div>--Pratik.<br></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Sat, Aug 24, 2019 at 3:31 PM Chao Yu <<a href="mailto:chao@kernel.org">chao@kernel.org</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">On 2019-8-24 17:49, Gao Xiang via Linux-erofs wrote:<br>
> Hi Pratik,<br>
> <br>
> On Sat, Aug 24, 2019 at 02:52:31PM +0530, Pratik Shinde wrote:<br>
>> Hi Gao,<br>
>> Yes I will make the suboption naming similar to that of mk2fs.<br>
> <br>
> Great! :)<br>
> <br>
>><br>
>> The reason I changed the position of 'checksum' field :<br>
>><br>
>> Since we are calculating the checksum of erofs_super_block structure and<br>
>> storing it in the same structure; we cannot include<br>
>> this field for actual crc calculations. Keeping it at the end makes it easy<br>
>> for me to calculate length of the data of which<br>
>> checksum needs to be calculated. I saw similar logic in other filesystems<br>
>> like ext4.<br>
> <br>
> No, that is just they didn't add checksum field at the beginning of its design.<br>
> I think you can leave chksum to 0, and calculate chksum and fill it, to be specfic:<br>
> <br>
> In the erofs-utils,<br>
> 1) fill .checksum to 0;<br>
> 2) calculate crc32c of the entire erofs_super_block;<br>
> 3) fill the real checksum to .checksum;<br>
> <br>
> In the kernel,<br>
> 1) read .checksum to a variable;<br>
> 2) fill .checksum to 0;<br>
> 3) calculate crc32c of the entire erofs_super_block;<br>
> 4) compare the given one and the calculated one;<br>
<br>
That's one way, FYI, the way used in ext4/f2fs now is:<br>
- calc [0, checksum]'s chksum<br>
- use above chksum as seed of chksum within range [chksum + chksum_size, end]<br>
- fill chksum value in range [checksum, chksum + chksum_size]<br>
<br>
Thanks,<br>
<br>
> <br>
> That is all :)<br>
> <br>
>><br>
>> We can write our own crc32() function. :) There is no problem. I thought<br>
>> zlib already provides one & we can use it.<br>
> <br>
> I think we can use crc32c() since I already wrote comments for erofs in 4.19.<br>
> <br>
> Looking forward to your next version :)<br>
> <br>
> Thanks,<br>
> Gao Xiang<br>
> <br>
>> anyways , I will write.<br>
>><br>
>> --Pratik.<br>
>><br>
>> On Sat, Aug 24, 2019 at 2:16 PM Gao Xiang <<a href="mailto:hsiangkao@gmx.com" target="_blank">hsiangkao@gmx.com</a>> wrote:<br>
>><br>
>>> Hi Pratik,<br>
>>><br>
>>> On Sat, Aug 24, 2019 at 01:11:58PM +0530, Pratik Shinde wrote:<br>
>>>> Adding code for superblock checksum calculation.<br>
>>>><br>
>>>> This patch adds following things:<br>
>>>> 1)Handle suboptions('-o') to mkfs utility.<br>
>>><br>
>>> Thanks for your patch. :)<br>
>>><br>
>>> Can we use "-O feature" instead in order to keep in line with mke2fs?<br>
>>><br>
>>>> 2)Add superblock checksum calculation(-o sb_cksum) as suboption.<br>
>>><br>
>>> ditto. and I think we can enable sbcrc by default since it is a compat<br>
>>> feature,<br>
>>> and add "-O nosbcrc" to disable it.<br>
>>><br>
>>>> 3)Calculate superblock checksum if feature is enabled.<br>
>>>><br>
>>>> Signed-off-by: Pratik Shinde <<a href="mailto:pratikshinde320@gmail.com" target="_blank">pratikshinde320@gmail.com</a>><br>
>>><br>
>>> And could you please also read my following comments and fix them.<br>
>>> and I'd like to accept your erofs-utils modification in advance. :)<br>
>>><br>
>>><br>
>>> But now you can see we are moving EROFS out of staging now as<br>
>>> the "real" part of Linux, this is the fundamental stuff of other<br>
>>> new features if we want to develop more actively... So we can wait<br>
>>> for the final result and add this new feature to kernel then...<br>
>>><br>
>>>> ---<br>
>>>> include/erofs/config.h | 1 +<br>
>>>> include/erofs_fs.h | 40 +++++++++++++++++++++----------------<br>
>>>> mkfs/main.c | 53<br>
>>> +++++++++++++++++++++++++++++++++++++++++++++++++-<br>
>>>> 3 files changed, 76 insertions(+), 18 deletions(-)<br>
>>>><br>
>>>> diff --git a/include/erofs/config.h b/include/erofs/config.h<br>
>>>> index 05fe6b2..40cd466 100644<br>
>>>> --- a/include/erofs/config.h<br>
>>>> +++ b/include/erofs/config.h<br>
>>>> @@ -22,6 +22,7 @@ struct erofs_configure {<br>
>>>> char *c_src_path;<br>
>>>> char *c_compr_alg_master;<br>
>>>> int c_compr_level_master;<br>
>>>> + int c_feature_flags;<br>
>>><br>
>>> we can add this to sbi like requirements...<br>
>>><br>
>>>> };<br>
>>>><br>
>>>> extern struct erofs_configure cfg;<br>
>>>> diff --git a/include/erofs_fs.h b/include/erofs_fs.h<br>
>>>> index 601b477..c9ef057 100644<br>
>>>> --- a/include/erofs_fs.h<br>
>>>> +++ b/include/erofs_fs.h<br>
>>>> @@ -20,25 +20,31 @@<br>
>>>> #define EROFS_REQUIREMENT_LZ4_0PADDING 0x00000001<br>
>>>> #define EROFS_ALL_REQUIREMENTS<br>
>>> EROFS_REQUIREMENT_LZ4_0PADDING<br>
>>>><br>
>>>> +/*<br>
>>>> + * feature definations.<br>
>>>> + */<br>
>>>> +#define EROFS_FEATURE_SB_CHKSUM 0x0001<br>
>>>> +<br>
>>>> +#define EROFS_HAS_COMPAT_FEATURE(super,mask) \<br>
>>>> + ( le32_to_cpu((super)->features) & (mask) )<br>
>>>> +<br>
>>>> struct erofs_super_block {<br>
>>>> /* 0 */__le32 magic; /* in the little endian */<br>
>>>> -/* 4 */__le32 checksum; /* crc32c(super_block) */<br>
>>>> -/* 8 */__le32 features; /* (aka. feature_compat) */<br>
>>>> -/* 12 */__u8 blkszbits; /* support block_size == PAGE_SIZE only<br>
>>> */<br>
>>>> -/* 13 */__u8 reserved;<br>
>>>> -<br>
>>>> -/* 14 */__le16 root_nid;<br>
>>>> -/* 16 */__le64 inos; /* total valid ino # (== f_files -<br>
>>> f_favail) */<br>
>>>> -<br>
>>>> -/* 24 */__le64 build_time; /* inode v1 time derivation */<br>
>>>> -/* 32 */__le32 build_time_nsec;<br>
>>>> -/* 36 */__le32 blocks; /* used for statfs */<br>
>>>> -/* 40 */__le32 meta_blkaddr;<br>
>>>> -/* 44 */__le32 xattr_blkaddr;<br>
>>>> -/* 48 */__u8 uuid[16]; /* 128-bit uuid for volume */<br>
>>>> -/* 64 */__u8 volume_name[16]; /* volume name */<br>
>>>> -/* 80 */__le32 requirements; /* (aka. feature_incompat) */<br>
>>>> -<br>
>>>> +/* 4 */__le32 features; /* (aka. feature_compat) */<br>
>>>> +/* 8 */__u8 blkszbits; /* support block_size == PAGE_SIZE only<br>
>>> */<br>
>>>> +/* 9 */__u8 reserved;<br>
>>>> +<br>
>>>> +/* 10 */__le16 root_nid;<br>
>>>> +/* 12 */__le64 inos; /* total valid ino # (== f_files -<br>
>>> f_favail) */<br>
>>>> +/* 20 */__le64 build_time; /* inode v1 time derivation */<br>
>>>> +/* 28 */__le32 build_time_nsec;<br>
>>>> +/* 32 */__le32 blocks; /* used for statfs */<br>
>>>> +/* 36 */__le32 meta_blkaddr;<br>
>>>> +/* 40 */__le32 xattr_blkaddr;<br>
>>>> +/* 44 */__u8 uuid[16]; /* 128-bit uuid for volume */<br>
>>>> +/* 60 */__u8 volume_name[16]; /* volume name */<br>
>>>> +/* 76 */__le32 requirements; /* (aka. feature_incompat) */<br>
>>>> +/* 80 */__le32 checksum; /* crc32c(super_block) */<br>
>>>> /* 84 */__u8 reserved2[44];<br>
>>><br>
>>> Why modifying the above?<br>
>>><br>
>>>> } __packed; /* 128 bytes */<br>
>>>><br>
>>>> diff --git a/mkfs/main.c b/mkfs/main.c<br>
>>>> index f127fe1..26e14a3 100644<br>
>>>> --- a/mkfs/main.c<br>
>>>> +++ b/mkfs/main.c<br>
>>>> @@ -13,12 +13,14 @@<br>
>>>> #include <limits.h><br>
>>>> #include <libgen.h><br>
>>>> #include <sys/stat.h><br>
>>>> +#include <zlib.h><br>
>>><br>
>>> I have no idea that we should introduce "zlib" just for crc32c currently...<br>
>>> Maybe we can add some independent crc32 function..<br>
>>><br>
>>> Thanks,<br>
>>> Gao Xiang<br>
>>><br>
>>>> #include "erofs/config.h"<br>
>>>> #include "erofs/print.h"<br>
>>>> #include "erofs/cache.h"<br>
>>>> #include "erofs/inode.h"<br>
>>>> #include "erofs/io.h"<br>
>>>> #include "erofs/compress.h"<br>
>>>> +#include "erofs/defs.h"<br>
>>>><br>
>>>> #define EROFS_SUPER_END (EROFS_SUPER_OFFSET + sizeof(struct<br>
>>> erofs_super_block))<br>
>>>><br>
>>>> @@ -31,6 +33,28 @@ static void usage(void)<br>
>>>> fprintf(stderr, " -EX[,...] X=extended options\n");<br>
>>>> }<br>
>>>><br>
>>>> +char *feature_opts[] = {<br>
>>>> + "sb_cksum", NULL<br>
>>>> +};<br>
>>>> +#define O_SB_CKSUM 0<br>
>>>> +<br>
>>>> +static int parse_feature_subopts(char *opts)<br>
>>>> +{<br>
>>>> + char *arg;<br>
>>>> +<br>
>>>> + while (*opts != '\0') {<br>
>>>> + switch(getsubopt(&opts, feature_opts, &arg)) {<br>
>>>> + case O_SB_CKSUM:<br>
>>>> + cfg.c_feature_flags |= EROFS_FEATURE_SB_CHKSUM;<br>
>>>> + break;<br>
>>>> + default:<br>
>>>> + erofs_err("incorrect suboption");<br>
>>>> + return -EINVAL;<br>
>>>> + }<br>
>>>> + }<br>
>>>> + return 0;<br>
>>>> +}<br>
>>>> +<br>
>>>> static int parse_extended_opts(const char *opts)<br>
>>>> {<br>
>>>> #define MATCH_EXTENTED_OPT(opt, token, keylen) \<br>
>>>> @@ -79,7 +103,7 @@ static int mkfs_parse_options_cfg(int argc, char<br>
>>> *argv[])<br>
>>>> {<br>
>>>> int opt, i;<br>
>>>><br>
>>>> - while ((opt = getopt(argc, argv, "d:z:E:")) != -1) {<br>
>>>> + while ((opt = getopt(argc, argv, "d:z:E:o:")) != -1) {<br>
>>>> switch (opt) {<br>
>>>> case 'z':<br>
>>>> if (!optarg) {<br>
>>>> @@ -113,6 +137,12 @@ static int mkfs_parse_options_cfg(int argc, char<br>
>>> *argv[])<br>
>>>> return opt;<br>
>>>> break;<br>
>>>><br>
>>>> + case 'o':<br>
>>>> + opt = parse_feature_subopts(optarg);<br>
>>>> + if (opt)<br>
>>>> + return opt;<br>
>>>> + break;<br>
>>>> +<br>
>>>> default: /* '?' */<br>
>>>> return -EINVAL;<br>
>>>> }<br>
>>>> @@ -144,6 +174,21 @@ static int mkfs_parse_options_cfg(int argc, char<br>
>>> *argv[])<br>
>>>> return 0;<br>
>>>> }<br>
>>>><br>
>>>> +u32 erofs_superblock_checksum(struct erofs_super_block *sb)<br>
>>>> +{<br>
>>>> + int offset;<br>
>>>> + u32 crc;<br>
>>>> +<br>
>>>> + offset = offsetof(struct erofs_super_block, checksum);<br>
>>>> + if (offset < 0 || offset > sizeof(struct erofs_super_block)) {<br>
>>>> + erofs_err("Invalid offset of checksum field: %d", offset);<br>
>>>> + return -1;<br>
>>>> + }<br>
>>>> + crc = crc32(~0, (const unsigned char *)sb,(size_t)offset);<br>
>>>> + erofs_dump("superblock checksum: 0x%x\n", crc);<br>
>>>> + return 0;<br>
>>>> +}<br>
>>>> +<br>
>>>> int erofs_mkfs_update_super_block(struct erofs_buffer_head *bh,<br>
>>>> erofs_nid_t root_nid)<br>
>>>> {<br>
>>>> @@ -155,6 +200,7 @@ int erofs_mkfs_update_super_block(struct<br>
>>> erofs_buffer_head *bh,<br>
>>>> .meta_blkaddr = sbi.meta_blkaddr,<br>
>>>> .xattr_blkaddr = 0,<br>
>>>> .requirements = cpu_to_le32(sbi.requirements),<br>
>>>> + .features = cpu_to_le32(cfg.c_feature_flags),<br>
>>>> };<br>
>>>> const unsigned int sb_blksize =<br>
>>>> round_up(EROFS_SUPER_END, EROFS_BLKSIZ);<br>
>>>> @@ -169,6 +215,11 @@ int erofs_mkfs_update_super_block(struct<br>
>>> erofs_buffer_head *bh,<br>
>>>> sb.blocks = cpu_to_le32(erofs_mapbh(NULL, true));<br>
>>>> sb.root_nid = cpu_to_le16(root_nid);<br>
>>>><br>
>>>> + if (EROFS_HAS_COMPAT_FEATURE(&sb, EROFS_FEATURE_SB_CHKSUM)) {<br>
>>>> + u32 crc = erofs_superblock_checksum(&sb);<br>
>>>> + sb.checksum = cpu_to_le32(crc);<br>
>>>> + }<br>
>>>> +<br>
>>>> buf = calloc(sb_blksize, 1);<br>
>>>> if (!buf) {<br>
>>>> erofs_err("Failed to allocate memory for sb: %s",<br>
>>>> --<br>
>>>> 2.9.3<br>
>>>><br>
>>><br>
</blockquote></div>