Re: [PATCH] xen-blkfront: Use the bitmap API when applicable
From: Christophe JAILLET
Date: Thu Dec 02 2021 - 14:07:25 EST
Le 02/12/2021 à 19:16, Joe Perches a écrit :
On Thu, 2021-12-02 at 19:12 +0100, Christophe JAILLET wrote:
Le 02/12/2021 à 07:12, Juergen Gross a écrit :
On 01.12.21 22:10, Christophe JAILLET wrote:
Use 'bitmap_zalloc()' to simplify code, improve the semantic and avoid
some open-coded arithmetic in allocator arguments.
Also change the corresponding 'kfree()' into 'bitmap_free()' to keep
consistency.
Use 'bitmap_copy()' to avoid an explicit 'memcpy()'
[]
diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
[]
@@ -442,16 +442,14 @@ static int xlbd_reserve_minors(unsigned int
minor, unsigned int nr)
if (end > nr_minors) {
unsigned long *bitmap, *old;
- bitmap = kcalloc(BITS_TO_LONGS(end), sizeof(*bitmap),
- GFP_KERNEL);
+ bitmap = bitmap_zalloc(end, GFP_KERNEL);
if (bitmap == NULL)
return -ENOMEM;
spin_lock(&minor_lock);
if (end > nr_minors) {
old = minors;
- memcpy(bitmap, minors,
- BITS_TO_LONGS(nr_minors) * sizeof(*bitmap));
+ bitmap_copy(bitmap, minors, nr_minors);
minors = bitmap;
nr_minors = BITS_TO_LONGS(end) * BITS_PER_LONG;
nr_minors = end;
?
No,
My understanding of the code is that if we lack space (end > nr_minors),
we need to allocate more. In such a case, we want to keep track of what
we have allocated, not what we needed.
The "padding" bits in the "long align" allocation, can be used later.
first call
----------
end = 65
nr_minors = 63
--> we need some space
--> we allocate 2 longs = 128 bits
--> we now use 65 bits of these 128 bits
new call
--------
end = 68
nr_minors = 128 (from previous call)
--> no need to reallocate
CJ