[PATCH v2025.09.y 23/49] fs: qemu_fw_cfg: make use of the automount

[Ahmad Fatoum <a.fatoum@pengutronix.de>]

We assume /mnt/fw_cfg to be the fw_cfg mount path at other places
already, so let's drop some complexity by just using the automount.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Link: https://lore.barebox.org/20251125062603.2614867-2-a.fatoum@pengutronix.de
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
(cherry picked from commit 332be0eec5f8b0683838fda48889efd8de76c9b1)
Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
---
 fs/devfs-core.c  |  6 ++++++
 fs/qemu_fw_cfg.c | 27 +++++----------------------
 include/driver.h |  2 ++
 3 files changed, 13 insertions(+), 22 deletions(-)

diff --git a/fs/devfs-core.c b/fs/devfs-core.c
index 92e7c5823ed0..4f8230e124eb 100644
--- a/fs/devfs-core.c
+++ b/fs/devfs-core.c
@@ -86,6 +86,12 @@ struct cdev *cdev_by_name(const char *filename)
 	return cdev_readlink(cdev);
 }
 
+struct device *device_find_by_file_path(const char *filename)
+{
+	struct cdev *cdev = cdev_by_name(devpath_to_name(filename));
+	return cdev ? cdev->dev : NULL;
+}
+
 struct cdev *cdev_by_device_node(struct device_node *node)
 {
 	struct cdev *cdev;
diff --git a/fs/qemu_fw_cfg.c b/fs/qemu_fw_cfg.c
index caf541574649..49115beeb21d 100644
--- a/fs/qemu_fw_cfg.c
+++ b/fs/qemu_fw_cfg.c
@@ -411,32 +411,15 @@ coredevice_initcall(qemu_fw_cfg_fs_init);
 
 static int qemu_fw_cfg_early_mount(void)
 {
-	struct cdev *cdev;
-	struct device *dev;
-	const char *mntpath;
-	int dirfd, fd;
-
-	cdev = cdev_by_name("fw_cfg");
-	if (!cdev)
-		return 0;
+	int fd;
 
 	/*
-	 * Trigger a mount, so ramfb device can be detected and
-	 * environment can be loaded
+	 * Also triggers the automount, so ramfb device can be detected
 	 */
-	mntpath = cdev_mount(cdev);
-	if (IS_ERR(mntpath))
-		return PTR_ERR(mntpath);
-
-	dirfd = open(mntpath, O_PATH | O_DIRECTORY);
-	if (dirfd < 0)
-		return dirfd;
-
-	fd = openat(dirfd, "by_name/etc/ramfb", O_WRONLY);
-	close(dirfd);
+	fd = open("/mnt/fw_cfg/by_name/etc/ramfb", O_WRONLY);
 	if (fd >= 0) {
-		dev = device_alloc("qemu-ramfb", DEVICE_ID_SINGLE);
-		dev->parent = cdev->dev;
+		struct device *dev = device_alloc("qemu-ramfb", DEVICE_ID_SINGLE);
+		dev->parent = device_find_by_file_path("/dev/fw_cfg");
 		dev->platform_data = (void *)(uintptr_t)fd;
 		platform_device_register(dev);
 	}
diff --git a/include/driver.h b/include/driver.h
index c130a3cd63fd..143ca18e4e39 100644
--- a/include/driver.h
+++ b/include/driver.h
@@ -477,6 +477,8 @@ int cdev_fdopen(struct cdev *cdev, unsigned long flags);
 int cdev_close(struct cdev *cdev);
 int cdev_flush(struct cdev *cdev);
 
+struct device *device_find_by_file_path(const char *filepath);
+
 typedef int (*cdev_alias_processor_t)(struct cdev *, void *data);
 
 #ifdef CONFIG_CDEV_ALIAS
-- 
2.47.3