[PATCH v3] erofs-utils: add --hard-dereference option

[Paul Meyer]

Add option --hard-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.

Co-authored-by: Leonard Cohnen <leonard.cohnen at gmail.com>
Signed-off-by: Paul Meyer <katexochen0 at gmail.com>
---
v3: Fix commit title and body, fix usage ordering.
v2: https://lore.kernel.org/all/20241212135630.15811-1-katexochen0@gmail.com/
v1: https://lore.kernel.org/all/20241211150734.97830-1-katexochen0@gmail.com/
---

 include/erofs/config.h | 1 +
 lib/inode.c            | 2 +-
 mkfs/main.c            | 5 +++++
 3 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/include/erofs/config.h b/include/erofs/config.h
index cff4cea..bb03e70 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_hard_dereference;
 
 #ifdef HAVE_LIBSELINUX
 	struct selabel_handle *sehnd;
diff --git a/lib/inode.c b/lib/inode.c
index 7e5c581..0404a8d 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_hard_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..b94923f 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},
+	{"hard-dereference", no_argument, NULL, 528},
 	{0, 0, 0, 0},
 };
 
@@ -174,6 +175,7 @@ static void usage(int argc, char **argv)
 		" --force-gid=#         set all file gids to # (# = GID)\n"
 		" --uid-offset=#        add offset # to all file uids (# = id offset)\n"
 		" --gid-offset=#        add offset # to all file gids (# = id offset)\n"
+		" --hard-dereference    dereference hardlinks, add links as separate inodes\n"
 		" --ignore-mtime        use build time instead of strict per-file modification time\n"
 		" --max-extent-bytes=#  set maximum decompressed extent size # in bytes\n"
 		" --mount-point=X       X=prefix of target fs path (default: /)\n"
@@ -846,6 +848,9 @@ static int mkfs_parse_options_cfg(int argc, char *argv[])
 			if (!strcmp(optarg, "none"))
 				erofstar.try_no_reorder = true;
 			break;
+		case 528:
+			cfg.c_hard_dereference = true;
+			break;
 		case 'V':
 			version();
 			exit(0);
-- 
2.47.0