[PATCH 2/8] char: misc: Introduce misc_find() helper

Tzung-Bi Shih
2026-04-27T13:47:42Z

Introduce misc_find() to search for a miscdevice by minor number in
`misc_list`. This helper requires `misc_mtx` to be held.

Use the new helper to reduce code duplication.

Signed-off-by: Tzung-Bi Shih <tzungbi@kernel.org>
---
drivers/char/misc.c | 43 +++++++++++++++++++++++--------------------
1 file changed, 23 insertions(+), 20 deletions(-)

diff --git a/drivers/char/misc.c b/drivers/char/misc.c
index e2bea4f01851..c26315577d65 100644
--- a/drivers/char/misc.c
+++ b/drivers/char/misc.c
@@ -116,22 +116,32 @@ static const struct seq_operations misc_seq_ops = {
};
#endif

+static struct miscdevice *misc_find(int minor)
+{
+ struct miscdevice *iter;
+
+ lockdep_assert_held(&misc_mtx);
+
+ list_for_each_entry(iter, &misc_list, list) {
+ if (iter->minor == minor)
+ return iter;
+ }
+
+ return NULL;
+}
+
static int misc_open(struct inode *inode, struct file *file)
{
int minor = iminor(inode);
- struct miscdevice *c = NULL, *iter;
+ struct miscdevice *c = NULL;
int err = -ENODEV;
const struct file_operations *new_fops = NULL;

mutex_lock(&misc_mtx);

- list_for_each_entry(iter, &misc_list, list) {
- if (iter->minor != minor)
- continue;
- c = iter;
- new_fops = fops_get(iter->fops);
- break;
- }
+ c = misc_find(minor);
+ if (c)
+ new_fops = fops_get(c->fops);

/* Only request module for fixed minor code */
if (!new_fops && minor < MISC_DYNAMIC_MINOR) {
@@ -139,13 +149,9 @@ static int misc_open(struct inode *inode, struct file *file)
request_module("char-major-%d-%d", MISC_MAJOR, minor);
mutex_lock(&misc_mtx);

- list_for_each_entry(iter, &misc_list, list) {
- if (iter->minor != minor)
- continue;
- c = iter;
- new_fops = fops_get(iter->fops);
- break;
- }
+ c = misc_find(minor);
+ if (c)
+ new_fops = fops_get(c->fops);
}

if (!new_fops)
@@ -229,13 +235,10 @@ int misc_register(struct miscdevice *misc)
return -EBUSY;
misc->minor = i;
} else {
- struct miscdevice *c;
int i;

- list_for_each_entry(c, &misc_list, list) {
- if (c->minor == misc->minor)
- return -EBUSY;
- }
+ if (misc_find(misc->minor))
+ return -EBUSY;

i = misc_minor_alloc(misc->minor);
if (i < 0)
--
2.51.0