[PATCH v3] erofs-utils: fsck: support extracting subtrees

[Inseob Kim]

Add --nid and --path options to fsck.erofs to allow users to check
or extract specific sub-directories or files instead of the entire
filesystem.

This is useful for targeted data recovery or verifying specific
image components without the overhead of a full traversal.

Signed-off-by: Inseob Kim <inseob at google.com>

---

v3: update the man page
v2: retrieve pnid correctly rather than pnid == nid hack
---
 fsck/main.c      | 82 ++++++++++++++++++++++++++++++++++++++++++------
 man/fsck.erofs.1 |  8 +++++
 2 files changed, 81 insertions(+), 9 deletions(-)

diff --git a/fsck/main.c b/fsck/main.c
index ab697be..16cc627 100644
--- a/fsck/main.c
+++ b/fsck/main.c
@@ -39,6 +39,8 @@ struct erofsfsck_cfg {
 	bool preserve_owner;
 	bool preserve_perms;
 	bool dump_xattrs;
+	erofs_nid_t nid;
+	const char *inode_path;
 	bool nosbcrc;
 };
 static struct erofsfsck_cfg fsckcfg;
@@ -59,6 +61,8 @@ static struct option long_options[] = {
 	{"offset", required_argument, 0, 12},
 	{"xattrs", no_argument, 0, 13},
 	{"no-xattrs", no_argument, 0, 14},
+	{"nid", required_argument, 0, 15},
+	{"path", required_argument, 0, 16},
 	{"no-sbcrc", no_argument, 0, 512},
 	{0, 0, 0, 0},
 };
@@ -110,6 +114,8 @@ static void usage(int argc, char **argv)
 		" --extract[=X]          check if all files are well encoded, optionally\n"
 		"                        extract to X\n"
 		" --offset=#             skip # bytes at the beginning of IMAGE\n"
+		" --nid=#                check or extract from the target inode of nid #\n"
+		" --path=X               check or extract from the target inode of path X\n"
 		" --no-sbcrc             bypass the superblock checksum verification\n"
 		" --[no-]xattrs          whether to dump extended attributes (default off)\n"
 		"\n"
@@ -245,6 +251,12 @@ static int erofsfsck_parse_options_cfg(int argc, char **argv)
 		case 14:
 			fsckcfg.dump_xattrs = false;
 			break;
+		case 15:
+			fsckcfg.nid = (erofs_nid_t)atoll(optarg);
+			break;
+		case 16:
+			fsckcfg.inode_path = optarg;
+			break;
 		case 512:
 			fsckcfg.nosbcrc = true;
 			break;
@@ -862,6 +874,22 @@ again:
 	return ret;
 }
 
+struct erofsfsck_get_parent_ctx {
+	struct erofs_dir_context ctx;
+	erofs_nid_t pnid;
+};
+
+static int erofsfsck_get_parent_cb(struct erofs_dir_context *ctx)
+{
+	struct erofsfsck_get_parent_ctx *pctx = (void *)ctx;
+
+	if (ctx->dot_dotdot && ctx->de_namelen == 2) {
+		pctx->pnid = ctx->de_nid;
+		return 1;
+	}
+	return 0;
+}
+
 static int erofsfsck_dirent_iter(struct erofs_dir_context *ctx)
 {
 	int ret;
@@ -1033,6 +1061,8 @@ int main(int argc, char *argv[])
 	fsckcfg.preserve_owner = fsckcfg.superuser;
 	fsckcfg.preserve_perms = fsckcfg.superuser;
 	fsckcfg.dump_xattrs = false;
+	fsckcfg.nid = 0;
+	fsckcfg.inode_path = NULL;
 
 	err = erofsfsck_parse_options_cfg(argc, argv);
 	if (err) {
@@ -1068,22 +1098,56 @@ int main(int argc, char *argv[])
 	if (fsckcfg.extract_path)
 		erofsfsck_hardlink_init();
 
-	if (erofs_sb_has_fragments(&g_sbi) && g_sbi.packed_nid > 0) {
-		err = erofs_packedfile_init(&g_sbi, false);
+	if (fsckcfg.inode_path) {
+		struct erofs_inode inode = { .sbi = &g_sbi };
+
+		err = erofs_ilookup(fsckcfg.inode_path, &inode);
 		if (err) {
-			erofs_err("failed to initialize packedfile: %s",
-				  erofs_strerror(err));
+			erofs_err("failed to lookup %s", fsckcfg.inode_path);
 			goto exit_hardlink;
 		}
+		fsckcfg.nid = inode.nid;
+	} else if (!fsckcfg.nid) {
+		fsckcfg.nid = g_sbi.root_nid;
+	}
 
-		err = erofsfsck_check_inode(g_sbi.packed_nid, g_sbi.packed_nid);
-		if (err) {
-			erofs_err("failed to verify packed file");
-			goto exit_packedinode;
+	if (!fsckcfg.inode_path && fsckcfg.nid == g_sbi.root_nid) {
+		if (erofs_sb_has_fragments(&g_sbi) && g_sbi.packed_nid > 0) {
+			err = erofs_packedfile_init(&g_sbi, false);
+			if (err) {
+				erofs_err("failed to initialize packedfile: %s",
+					  erofs_strerror(err));
+				goto exit_hardlink;
+			}
+
+			err = erofsfsck_check_inode(g_sbi.packed_nid, g_sbi.packed_nid);
+			if (err) {
+				erofs_err("failed to verify packed file");
+				goto exit_packedinode;
+			}
+		}
+	}
+
+	{
+		erofs_nid_t pnid = fsckcfg.nid;
+
+		if (fsckcfg.nid != g_sbi.root_nid) {
+			struct erofs_inode inode = { .sbi = &g_sbi, .nid = fsckcfg.nid };
+
+			if (!erofs_read_inode_from_disk(&inode) &&
+			    S_ISDIR(inode.i_mode)) {
+				struct erofsfsck_get_parent_ctx ctx = {
+					.ctx.dir = &inode,
+					.ctx.cb = erofsfsck_get_parent_cb,
+				};
+
+				if (erofs_iterate_dir(&ctx.ctx, false) == 1)
+					pnid = ctx.pnid;
+			}
 		}
+		err = erofsfsck_check_inode(pnid, fsckcfg.nid);
 	}
 
-	err = erofsfsck_check_inode(g_sbi.root_nid, g_sbi.root_nid);
 	if (fsckcfg.corrupted) {
 		if (!fsckcfg.extract_path)
 			erofs_err("Found some filesystem corruption");
diff --git a/man/fsck.erofs.1 b/man/fsck.erofs.1
index fb255b4..0f698da 100644
--- a/man/fsck.erofs.1
+++ b/man/fsck.erofs.1
@@ -37,6 +37,14 @@ Optionally extract contents of the \fIIMAGE\fR to \fIdirectory\fR.
 .B "--no-sbcrc"
 Bypass the on-disk superblock checksum verification.
 .TP
+.BI "\-\-nid=" #
+Specify the target inode by its NID for checking or extraction.
+The default is the root inode.
+.TP
+.BI "\-\-path=" path
+Specify the target inode by its path for checking or extraction. If both
+\fB\-\-nid\fR and \fB\-\-path\fR are specified, \fB\-\-path\fR takes precedence.
+.TP
 .BI "--[no-]xattrs"
 Whether to dump extended attributes during extraction (default off).
 .TP
-- 
2.53.0.414.gf7e9f6c205-goog