Liu Bo
2011-Aug-20 02:17 UTC
[PATCH v2] Btrfs: use do_div to avoid compile errors on 32bit box
When doing div operation of u64 type, we need to be careful and use do_div
to avoid compile ERROR on 32bit box:
"ERROR: "__udivdi3" [fs/btrfs/btrfs.ko] undefined!
make[1]: *** [__modpost] Error 1
v1->v2:
- fix stupid do_div() with type "signed integer".
Signed-off-by: Liu Bo <liubo2009@cn.fujitsu.com>
---
fs/btrfs/extent-tree.c | 11 ++++++-----
1 files changed, 6 insertions(+), 5 deletions(-)
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 80d6148..e43e4f1 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -6735,9 +6735,10 @@ int btrfs_can_relocate(struct btrfs_root *root, u64
bytenr)
struct btrfs_fs_devices *fs_devices = root->fs_info->fs_devices;
struct btrfs_device *device;
u64 min_free;
+ u32 dev_min = 1;
+ u32 dev_nr = 0;
+ u32 dup = 2;
int index;
- int dev_nr = 0;
- int dev_min = 1;
int full = 0;
int ret = 0;
@@ -6796,14 +6797,14 @@ int btrfs_can_relocate(struct btrfs_root *root, u64
bytenr)
index = get_block_group_index(block_group);
if (index == 0) {
dev_min = 4;
- min_free /= 2;
+ do_div(min_free, dup);
} else if (index == 1) {
dev_min = 2;
} else if (index == 2) {
- min_free *= 2;
+ min_free *= dup;
} else if (index == 3) {
dev_min = fs_devices->rw_devices;
- min_free /= dev_min;
+ do_div(min_free, dev_min);
}
mutex_lock(&root->fs_info->chunk_mutex);
--
1.6.5.2
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Josef Bacik
2011-Aug-20 12:21 UTC
Re: [PATCH v2] Btrfs: use do_div to avoid compile errors on 32bit box
On 08/19/2011 10:17 PM, Liu Bo wrote:> When doing div operation of u64 type, we need to be careful and use do_div > to avoid compile ERROR on 32bit box: > > "ERROR: "__udivdi3" [fs/btrfs/btrfs.ko] undefined! > make[1]: *** [__modpost] Error 1 > > v1->v2: > - fix stupid do_div() with type "signed integer". > > Signed-off-by: Liu Bo <liubo2009@cn.fujitsu.com> > --- > fs/btrfs/extent-tree.c | 11 ++++++----- > 1 files changed, 6 insertions(+), 5 deletions(-) > > diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c > index 80d6148..e43e4f1 100644 > --- a/fs/btrfs/extent-tree.c > +++ b/fs/btrfs/extent-tree.c > @@ -6735,9 +6735,10 @@ int btrfs_can_relocate(struct btrfs_root *root, u64 bytenr) > struct btrfs_fs_devices *fs_devices = root->fs_info->fs_devices; > struct btrfs_device *device; > u64 min_free; > + u32 dev_min = 1; > + u32 dev_nr = 0; > + u32 dup = 2; > int index; > - int dev_nr = 0; > - int dev_min = 1; > int full = 0; > int ret = 0; > > @@ -6796,14 +6797,14 @@ int btrfs_can_relocate(struct btrfs_root *root, u64 bytenr) > index = get_block_group_index(block_group); > if (index == 0) { > dev_min = 4; > - min_free /= 2; > + do_div(min_free, dup);I think Linus was less complaining about how you''re dividing here and more about the fact that you are. A divide by 2 is the same as a >> 1. I''ll send a patch to fix this. Thanks, Josef -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Linus Torvalds
2011-Aug-21 01:04 UTC
Re: [PATCH v2] Btrfs: use do_div to avoid compile errors on 32bit box
On Sat, Aug 20, 2011 at 5:21 AM, Josef Bacik <josef@redhat.com> wrote:> > I think Linus was less complaining about how you''re dividing here and > more about the fact that you are. A divide by 2 is the same as a >> 1. > I''ll send a patch to fix this. Thanks,Indeed. A single-bit 64-bit "double shift" may be a few cycles, but it''s still pretty damn cheap. Especially when compared to a 64x32 bit divide. We absolutely don''t want to do "do_div()" in order to divide by the constant 2. Linus