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

[Pratik Shinde <pratikshinde320@gmail.com>]

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Hi Gao,

I completely understand your concern.You can drop this patch for now.
Once erofs makes it 'fs/' please do reconsider implementing it.

One more thing, can we still send non feature patches?

--Pratik


On Sat, 24 Aug, 2019, 7:30 PM Gao Xiang, <hsiangkao@aol.com> wrote:

> 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
> >
>

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