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

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  [PATCH 1/2] drivers: char: Replace bit operation functions with IDA  allocator. Varsha Rao <rvarsha016@gmail.com> - 2017-04-10 09:00 +0200
    Re: [PATCH 1/2] drivers: char: Replace bit operation functions with  IDA allocator. Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-04-10 15:50 +0200

#1619666 — [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@gmail.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

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#1619943 — Re: [PATCH 1/2] drivers: char: Replace bit operation functions with IDA allocator.

On Mon, Apr 10, 2017 at 12:28:59PM +0530, Varsha Rao wrote:
> 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.

The allocation is different than the bitfield searching is?  How
exactly?  What is the old result vs. the new result of this change?

How did you test this?

You have to really sell this change, right now it looks pretty
pointless...

thanks,

greg k-h

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