[PATCH 2/4] fs: remove the default automount when a cdev is removed

[Sascha Hauer <s.hauer@pengutronix.de>]

cdev_create_default_automount() registers an automount point at
/mnt/<cdevname> which runs "mount <cdevname>" when the directory is first
walked into. It never had a counterpart, so when the cdev goes away the
directory and the automount entry stay behind, pointing at a device that
no longer exists.

Unplugging a USB mass storage device leaves /mnt/disk0 and /mnt/disk0.0
around, and repartitioning at runtime leaves an entry for every partition
that doesn't come back - remove the two partitions of a disk and create a
single one instead and /mnt/disk0.1 is still there afterwards. The stale
entries are replaced once the same cdev name is registered again, since
automount_add() drops a previous entry for the same dentry, which is why
this went unnoticed for so long. Names that are not reused stay stale
forever though.

Add cdev_remove_default_automount() and call it from devfs_remove().
Whether a cdev has an automount is remembered in a new DEVFS_HAS_AUTOMOUNT
flag rather than being guessed from the path, so that an automount point
somebody registered by hand is never removed just because a cdev happens
to share its name.

Removal is safe while a filesystem is mounted: mounting holds the cdev
open via fsdev_open_cdev(), so devfs_remove() bails out with -EBUSY long
before we get here. automount_remove() looks the path up without
LOOKUP_DIRECTORY or LOOKUP_PARENT, so follow_automount() returns -EISDIR
and the lookup doesn't trigger the automount it is about to remove.

Fixes: 85dffaacfa ("fs: Create automount entries for the default mount pathes")
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Assisted-by: Claude:claude-opus-5
---
 fs/devfs-core.c  |  2 ++
 fs/fs.c          | 20 +++++++++++++++++++-
 include/driver.h |  5 +++++
 3 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/fs/devfs-core.c b/fs/devfs-core.c
index b9e34f83bb..8b023009a0 100644
--- a/fs/devfs-core.c
+++ b/fs/devfs-core.c
@@ -605,6 +605,8 @@ int devfs_remove(struct cdev *cdev)
 
 	devfs_remove_aliases(cdev);
 
+	cdev_remove_default_automount(cdev);
+
 	list_for_each_entry_safe(c, tmp, &cdev->partitions, partition_entry)
 		cdevfs_del_partition(c);
 
diff --git a/fs/fs.c b/fs/fs.c
index ce41f23f88..f109e31075 100644
--- a/fs/fs.c
+++ b/fs/fs.c
@@ -3493,12 +3493,30 @@ void cdev_create_default_automount(struct cdev *cdev)
 	cmd = basprintf("mount %s", cdev->name);
 
 	make_directory(path);
-	automount_add(path, cmd);
+	if (!automount_add(path, cmd))
+		cdev->flags |= DEVFS_HAS_AUTOMOUNT;
 
 	free(cmd);
 	free(path);
 }
 
+void cdev_remove_default_automount(struct cdev *cdev)
+{
+	char *path;
+
+	if (!(cdev->flags & DEVFS_HAS_AUTOMOUNT))
+		return;
+
+	path = basprintf("/mnt/%s", cdev->name);
+
+	automount_remove(path);
+	rmdir(path);
+
+	cdev->flags &= ~DEVFS_HAS_AUTOMOUNT;
+
+	free(path);
+}
+
 void automount_print(void)
 {
 	struct automount *am;
diff --git a/include/driver.h b/include/driver.h
index 77b9b87695..b0602e6f16 100644
--- a/include/driver.h
+++ b/include/driver.h
@@ -572,6 +572,7 @@ extern struct list_head cdev_list;
 #define DEVFS_PARTITION_FOR_FIXUP	(1U << 13)
 #define DEVFS_WRITE_AUTOERASE		(1U << 14)
 #define DEVFS_PARTITION_CAN_OVERLAP	(1U << 15)
+#define DEVFS_HAS_AUTOMOUNT		(1U << 16)
 
 /**
  * cdev_write_requires_erase - Check whether writes must be done to erased blocks
@@ -615,10 +616,14 @@ cdev_find_child_by_gpt_typeuuid(struct cdev *cdev, const guid_t *typeuuid);
 
 #ifdef CONFIG_FS_AUTOMOUNT
 void cdev_create_default_automount(struct cdev *cdev);
+void cdev_remove_default_automount(struct cdev *cdev);
 #else
 static inline void cdev_create_default_automount(struct cdev *cdev)
 {
 }
+static inline void cdev_remove_default_automount(struct cdev *cdev)
+{
+}
 #endif
 
 #define DEVFS_PARTITION_APPEND		0

-- 
2.47.3