Re: [PATCH] erofs-utils: add --hardlink-dereference option

[Gao Xiang]

Hi Paul,

On 2024/12/11 23:07, Paul Meyer wrote:

Add option --hardlink-dereference to dereference hardlinks when
creating an image. Instead of reusing the inode, hardlinks are added
as separate inodes. This is useful for reproducible builds, when the
rootfs is space-optimized using hardlinks on some machines, but not on
others.

Thanks for the patch!

Yet I fail to parse the feature, why this feature is useful
for reproducible builds? IOWs, without this feature (or
hardlinks are used), what's the exact impact that you don't
want to?

Thanks,
Gao Xiang

Co-authored-by: Leonard Cohnen <leonard.coh...@gmail.com>
Signed-off-by: Paul Meyer <katexoch...@gmail.com>
---
  include/erofs/config.h | 1 +
  lib/inode.c            | 2 +-
  mkfs/main.c            | 4 ++++
  3 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/include/erofs/config.h b/include/erofs/config.h
index cff4cea..8399afb 100644
--- a/include/erofs/config.h
+++ b/include/erofs/config.h
@@ -58,6 +58,7 @@ struct erofs_configure {
        bool c_extra_ea_name_prefixes;
        bool c_xattr_name_filter;
        bool c_ovlfs_strip;
+       bool c_hardlink_dereference;

#ifdef HAVE_LIBSELINUX

        struct selabel_handle *sehnd;
diff --git a/lib/inode.c b/lib/inode.c
index 7e5c581..5d181b3 100644
--- a/lib/inode.c
+++ b/lib/inode.c
@@ -1141,7 +1141,7 @@ static struct erofs_inode *erofs_iget_from_srcpath(struct 
erofs_sb_info *sbi,
         * hard-link, just return it. Also don't lookup for directories
         * since hard-link directory isn't allowed.
         */
-       if (!S_ISDIR(st.st_mode)) {
+       if (!S_ISDIR(st.st_mode) && (!cfg.c_hardlink_dereference)) {
                inode = erofs_iget(st.st_dev, st.st_ino);
                if (inode)
                        return inode;
diff --git a/mkfs/main.c b/mkfs/main.c
index d422787..09e39f5 100644
--- a/mkfs/main.c
+++ b/mkfs/main.c
@@ -85,6 +85,7 @@ static struct option long_options[] = {
        {"mkfs-time", no_argument, NULL, 525},
        {"all-time", no_argument, NULL, 526},
        {"sort", required_argument, NULL, 527},
+       {"hardlink-dereference", no_argument, NULL, 528},
        {0, 0, 0, 0},
  };

@@ -846,6 +847,9 @@ static int mkfs_parse_options_cfg(int argc, char *argv[])

                        if (!strcmp(optarg, "none"))
                                erofstar.try_no_reorder = true;
                        break;
+               case 528:
+                       cfg.c_hardlink_dereference = true;
+                       break;
                case 'V':
                        version();
                        exit(0);