From fec73a61ce86cd0ee12b5596f66ac2f060a9936e Mon Sep 17 00:00:00 2001
From: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Date: Wed, 21 Jan 2026 20:53:35 +0900
Subject: [PATCH] libnilfs: allow opening nilfs by resolving backing device

Introduce a new open flag NILFS_OPEN_SRCHDEV.

If this flag is set and the 'dev' argument is a file or directory on a
NILFS filesystem, nilfs_open() automatically locates the backing block
device.

The logic calls the internal helper function nilfs_lookup_device() to
retrieve the device ID from the given path and resolve the canonical
device path (e.g. "/dev/sda1") via sysfs.

To support this, the source file "lookup_device.c" is added to the build
list in lib/Makefile.am.

This feature eliminates the need for users or tools to explicitly specify
the block device path when operating on a mounted NILFS filesystem.

Signed-off-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
---
 include/nilfs.h |  1 +
 lib/Makefile.am |  2 +-
 lib/nilfs.c     | 13 +++++++++++++
 3 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/include/nilfs.h b/include/nilfs.h
index 111a7e6..893fb2f 100644
--- a/include/nilfs.h
+++ b/include/nilfs.h
@@ -76,6 +76,7 @@ struct nilfs_layout {
 #define NILFS_OPEN_WRONLY	0x0004	/* Open NILFS API in write only mode */
 #define NILFS_OPEN_RDWR		0x0008	/* Open NILFS API in read/write mode */
 #define NILFS_OPEN_GCLK		0x1000	/* Open GC lock primitive */
+#define NILFS_OPEN_SRCHDEV	0x2000	/* Search device bound to the node */
 
 
 struct nilfs *nilfs_open(const char *dev, const char *dir, int flags);
diff --git a/lib/Makefile.am b/lib/Makefile.am
index ca6c5db..dcfb495 100644
--- a/lib/Makefile.am
+++ b/lib/Makefile.am
@@ -27,7 +27,7 @@ libnilfs_REVISION = 0
 libnilfs_AGE = 0
 libnilfs_VERSIONINFO = $(libnilfs_CURRENT):$(libnilfs_REVISION):$(libnilfs_AGE)
 
-libnilfs_la_SOURCES = nilfs.c sb.c
+libnilfs_la_SOURCES = nilfs.c sb.c lookup_device.c
 libnilfs_la_LDFLAGS = -version-info $(libnilfs_VERSIONINFO)
 libnilfs_la_LIBADD = librealpath.la libcrc32.la $(LIB_POSIX_SEM)
 
diff --git a/lib/nilfs.c b/lib/nilfs.c
index 25bc95d..90821e4 100644
--- a/lib/nilfs.c
+++ b/lib/nilfs.c
@@ -82,6 +82,7 @@
 #include "util.h"
 #include "pathnames.h"
 #include "realpath.h"
+#include "lookup_device.h"	/* nilfs_lookup_device() */
 
 /**
  * struct nilfs - nilfs object
@@ -408,6 +409,7 @@ static int nilfs_open_sem(struct nilfs *nilfs)
 struct nilfs *nilfs_open(const char *dev, const char *dir, int flags)
 {
 	struct nilfs *nilfs;
+	char *backdev;
 	uint64_t features;
 	int ret;
 
@@ -429,6 +431,15 @@ struct nilfs *nilfs_open(const char *dev, const char *dir, int flags)
 	nilfs->n_opts = 0;
 	nilfs->n_mincno = NILFS_CNO_MIN;
 	memset(nilfs->n_sems, 0, sizeof(nilfs->n_sems));
+	backdev = NULL;
+
+	if ((flags & NILFS_OPEN_SRCHDEV) && dev) {
+		ret = nilfs_lookup_device(dev, &backdev);
+		if (unlikely(ret < 0))
+			goto out_fd;
+		else if (ret > 0)
+			dev = backdev;  /* replace dev in this function */
+	}
 
 	if (flags & NILFS_OPEN_RAW) {
 		if (dev == NULL) {
@@ -499,6 +510,7 @@ struct nilfs *nilfs_open(const char *dev, const char *dir, int flags)
 	}
 
 	/* success */
+	free(backdev);
 	return nilfs;
 
 	/* error */
@@ -508,6 +520,7 @@ out_fd:
 	if (nilfs->n_iocfd >= 0)
 		close(nilfs->n_iocfd);
 
+	free(backdev);
 	free(nilfs->n_dev);
 	free(nilfs->n_ioc);
 	free(nilfs->n_sb);