linux-kernel - [PATCH 1/2] drivers: char: Replace bit operation functions with IDA allocator.

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Date:   Mon, 10 Apr 2017 12:28:59 +0530
From:   Varsha Rao <rvarsha016@...il.com>
To:     Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Matthew Wilcox <mawilcox@...rosoft.com>
Cc:     linux-kernel@...r.kernel.org
Subject: [PATCH 1/2] drivers: char: Replace bit operation functions with IDA
 allocator.

Replace bit operation functions with IDA allocator functions. As IDA
allocation is simpler, faster, more space efficient and it generates
small integer IDs which can be used as minor device numbers.

Signed-off-by: Varsha Rao <rvarsha016@...il.com>
---
 drivers/char/misc.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/drivers/char/misc.c b/drivers/char/misc.c
index c9cd1ea..5786281 100644
--- a/drivers/char/misc.c
+++ b/drivers/char/misc.c
@@ -60,7 +60,7 @@ static DEFINE_MUTEX(misc_mtx);
  * Assigned numbers, used for dynamic minors
  */
 #define DYNAMIC_MINORS 64 /* like dynamic majors */
-static DECLARE_BITMAP(misc_minors, DYNAMIC_MINORS);
+static DEFINE_IDA(misc_minors_ida);
 
 #ifdef CONFIG_PROC_FS
 static void *misc_seq_start(struct seq_file *seq, loff_t *pos)
@@ -193,14 +193,18 @@ int misc_register(struct miscdevice *misc)
 	mutex_lock(&misc_mtx);
 
 	if (is_dynamic) {
-		int i = find_first_zero_bit(misc_minors, DYNAMIC_MINORS);
+		int i = ida_simple_get(&misc_minors_ida, 0,
+				       DYNAMIC_MINORS, GFP_KERNEL);
 
 		if (i >= DYNAMIC_MINORS) {
 			err = -EBUSY;
 			goto out;
-		}
+		} else if (i < 0) {
+			err = i;
+			goto out;
+		} else {
 		misc->minor = DYNAMIC_MINORS - i - 1;
-		set_bit(i, misc_minors);
+		}
 	} else {
 		struct miscdevice *c;
 
@@ -222,7 +226,7 @@ int misc_register(struct miscdevice *misc)
 			int i = DYNAMIC_MINORS - misc->minor - 1;
 
 			if (i < DYNAMIC_MINORS && i >= 0)
-				clear_bit(i, misc_minors);
+				ida_simple_remove(&misc_minors_ida, i);
 			misc->minor = MISC_DYNAMIC_MINOR;
 		}
 		err = PTR_ERR(misc->this_device);
@@ -258,7 +262,7 @@ void misc_deregister(struct miscdevice *misc)
 	list_del(&misc->list);
 	device_destroy(misc_class, MKDEV(MISC_MAJOR, misc->minor));
 	if (i < DYNAMIC_MINORS && i >= 0)
-		clear_bit(i, misc_minors);
+		ida_simple_remove(&misc_minors_ida, i);
 	mutex_unlock(&misc_mtx);
 }
 
-- 
2.9.3