[PATCH] erofs-utils: code for superblock checksum calculation.
Gao Xiang
hsiangkao at aol.com
Sat Aug 24 19:49:47 AEST 2019
Hi Pratik,
On Sat, Aug 24, 2019 at 02:52:31PM +0530, Pratik Shinde wrote:
> Hi Gao,
> Yes I will make the suboption naming similar to that of mk2fs.
Great! :)
>
> The reason I changed the position of 'checksum' field :
>
> Since we are calculating the checksum of erofs_super_block structure and
> storing it in the same structure; we cannot include
> this field for actual crc calculations. Keeping it at the end makes it easy
> for me to calculate length of the data of which
> checksum needs to be calculated. I saw similar logic in other filesystems
> like ext4.
No, that is just they didn't add checksum field at the beginning of its design.
I think you can leave chksum to 0, and calculate chksum and fill it, to be specfic:
In the erofs-utils,
1) fill .checksum to 0;
2) calculate crc32c of the entire erofs_super_block;
3) fill the real checksum to .checksum;
In the kernel,
1) read .checksum to a variable;
2) fill .checksum to 0;
3) calculate crc32c of the entire erofs_super_block;
4) compare the given one and the calculated one;
That is all :)
>
> We can write our own crc32() function. :) There is no problem. I thought
> zlib already provides one & we can use it.
I think we can use crc32c() since I already wrote comments for erofs in 4.19.
Looking forward to your next version :)
Thanks,
Gao Xiang
> anyways , I will write.
>
> --Pratik.
>
> On Sat, Aug 24, 2019 at 2:16 PM Gao Xiang <hsiangkao at gmx.com> wrote:
>
> > Hi Pratik,
> >
> > On Sat, Aug 24, 2019 at 01:11:58PM +0530, Pratik Shinde wrote:
> > > Adding code for superblock checksum calculation.
> > >
> > > This patch adds following things:
> > > 1)Handle suboptions('-o') to mkfs utility.
> >
> > Thanks for your patch. :)
> >
> > Can we use "-O feature" instead in order to keep in line with mke2fs?
> >
> > > 2)Add superblock checksum calculation(-o sb_cksum) as suboption.
> >
> > ditto. and I think we can enable sbcrc by default since it is a compat
> > feature,
> > and add "-O nosbcrc" to disable it.
> >
> > > 3)Calculate superblock checksum if feature is enabled.
> > >
> > > Signed-off-by: Pratik Shinde <pratikshinde320 at gmail.com>
> >
> > And could you please also read my following comments and fix them.
> > and I'd like to accept your erofs-utils modification in advance. :)
> >
> >
> > But now you can see we are moving EROFS out of staging now as
> > the "real" part of Linux, this is the fundamental stuff of other
> > new features if we want to develop more actively... So we can wait
> > for the final result and add this new feature to kernel then...
> >
> > > ---
> > > include/erofs/config.h | 1 +
> > > include/erofs_fs.h | 40 +++++++++++++++++++++----------------
> > > mkfs/main.c | 53
> > +++++++++++++++++++++++++++++++++++++++++++++++++-
> > > 3 files changed, 76 insertions(+), 18 deletions(-)
> > >
> > > 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;
> >
> > we can add this to sbi like requirements...
> >
> > > };
> > >
> > > extern struct erofs_configure cfg;
> > > diff --git a/include/erofs_fs.h b/include/erofs_fs.h
> > > index 601b477..c9ef057 100644
> > > --- a/include/erofs_fs.h
> > > +++ b/include/erofs_fs.h
> > > @@ -20,25 +20,31 @@
> > > #define EROFS_REQUIREMENT_LZ4_0PADDING 0x00000001
> > > #define EROFS_ALL_REQUIREMENTS
> > EROFS_REQUIREMENT_LZ4_0PADDING
> > >
> > > +/*
> > > + * feature definations.
> > > + */
> > > +#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) */
> > > -/* 8 */__le32 features; /* (aka. feature_compat) */
> > > -/* 12 */__u8 blkszbits; /* support block_size == PAGE_SIZE only
> > */
> > > -/* 13 */__u8 reserved;
> > > -
> > > -/* 14 */__le16 root_nid;
> > > -/* 16 */__le64 inos; /* total valid ino # (== f_files -
> > f_favail) */
> > > -
> > > -/* 24 */__le64 build_time; /* inode v1 time derivation */
> > > -/* 32 */__le32 build_time_nsec;
> > > -/* 36 */__le32 blocks; /* used for statfs */
> > > -/* 40 */__le32 meta_blkaddr;
> > > -/* 44 */__le32 xattr_blkaddr;
> > > -/* 48 */__u8 uuid[16]; /* 128-bit uuid for volume */
> > > -/* 64 */__u8 volume_name[16]; /* volume name */
> > > -/* 80 */__le32 requirements; /* (aka. feature_incompat) */
> > > -
> > > +/* 4 */__le32 features; /* (aka. feature_compat) */
> > > +/* 8 */__u8 blkszbits; /* support block_size == PAGE_SIZE only
> > */
> > > +/* 9 */__u8 reserved;
> > > +
> > > +/* 10 */__le16 root_nid;
> > > +/* 12 */__le64 inos; /* total valid ino # (== f_files -
> > f_favail) */
> > > +/* 20 */__le64 build_time; /* inode v1 time derivation */
> > > +/* 28 */__le32 build_time_nsec;
> > > +/* 32 */__le32 blocks; /* used for statfs */
> > > +/* 36 */__le32 meta_blkaddr;
> > > +/* 40 */__le32 xattr_blkaddr;
> > > +/* 44 */__u8 uuid[16]; /* 128-bit uuid for volume */
> > > +/* 60 */__u8 volume_name[16]; /* volume name */
> > > +/* 76 */__le32 requirements; /* (aka. feature_incompat) */
> > > +/* 80 */__le32 checksum; /* crc32c(super_block) */
> > > /* 84 */__u8 reserved2[44];
> >
> > Why modifying the above?
> >
> > > } __packed; /* 128 bytes */
> > >
> > > diff --git a/mkfs/main.c b/mkfs/main.c
> > > index f127fe1..26e14a3 100644
> > > --- a/mkfs/main.c
> > > +++ b/mkfs/main.c
> > > @@ -13,12 +13,14 @@
> > > #include <limits.h>
> > > #include <libgen.h>
> > > #include <sys/stat.h>
> > > +#include <zlib.h>
> >
> > I have no idea that we should introduce "zlib" just for crc32c currently...
> > Maybe we can add some independent crc32 function..
> >
> > Thanks,
> > Gao Xiang
> >
> > > #include "erofs/config.h"
> > > #include "erofs/print.h"
> > > #include "erofs/cache.h"
> > > #include "erofs/inode.h"
> > > #include "erofs/io.h"
> > > #include "erofs/compress.h"
> > > +#include "erofs/defs.h"
> > >
> > > #define EROFS_SUPER_END (EROFS_SUPER_OFFSET + sizeof(struct
> > erofs_super_block))
> > >
> > > @@ -31,6 +33,28 @@ static void usage(void)
> > > fprintf(stderr, " -EX[,...] X=extended options\n");
> > > }
> > >
> > > +char *feature_opts[] = {
> > > + "sb_cksum", NULL
> > > +};
> > > +#define O_SB_CKSUM 0
> > > +
> > > +static int parse_feature_subopts(char *opts)
> > > +{
> > > + char *arg;
> > > +
> > > + 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 +103,7 @@ static int mkfs_parse_options_cfg(int argc, char
> > *argv[])
> > > {
> > > int opt, i;
> > >
> > > - while ((opt = getopt(argc, argv, "d:z:E:")) != -1) {
> > > + while ((opt = getopt(argc, argv, "d:z:E:o:")) != -1) {
> > > switch (opt) {
> > > case 'z':
> > > if (!optarg) {
> > > @@ -113,6 +137,12 @@ 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 +174,21 @@ static int mkfs_parse_options_cfg(int argc, char
> > *argv[])
> > > return 0;
> > > }
> > >
> > > +u32 erofs_superblock_checksum(struct erofs_super_block *sb)
> > > +{
> > > + int offset;
> > > + u32 crc;
> > > +
> > > + offset = offsetof(struct erofs_super_block, checksum);
> > > + if (offset < 0 || offset > sizeof(struct erofs_super_block)) {
> > > + erofs_err("Invalid offset of checksum field: %d", offset);
> > > + return -1;
> > > + }
> > > + crc = crc32(~0, (const unsigned char *)sb,(size_t)offset);
> > > + erofs_dump("superblock checksum: 0x%x\n", crc);
> > > + return 0;
> > > +}
> > > +
> > > int erofs_mkfs_update_super_block(struct erofs_buffer_head *bh,
> > > erofs_nid_t root_nid)
> > > {
> > > @@ -155,6 +200,7 @@ 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 +215,11 @@ 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)) {
> > > + 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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