On 05/10/2013 13:20, David Sterba wrote:
On Tue, May 07, 2013 at 10:44:05AM +0200, Stefan Behrens wrote:
On Mon, 6 May 2013 23:11:20 +0200, David Sterba wrote:
Superblock is always 4k, but metadata blocks may be larger. We have to
use the appropriate block size when doing checksums, otherwise they're
wrong.
Signed-off-by: David Sterba <dsterba@xxxxxxx>
---
btrfs-image.c | 27 +++++++++++++++++++++++----
1 file changed, 23 insertions(+), 4 deletions(-)
diff --git a/btrfs-image.c b/btrfs-image.c
index 188291c..dca7a28 100644
--- a/btrfs-image.c
+++ b/btrfs-image.c
@@ -469,6 +469,16 @@ static int read_data_extent(struct metadump_struct *md,
return 0;
}
+static int is_sb_offset(u64 offset) {
+ switch (offset) {
+ case 65536:
+ case 67108864:
+ case 274877906944:
Using btrfs_sb_offset() and an if statement would produce the same code
and would be more readable.
It was there originally, but this function is called for each block and
I've optimized it a bit right away. I'll add a comment.
You have not optimized it. gcc does not generate a jump table with 274
billion entries (I have verified it). The code is the same in both cases.
Here is the C code diff:
*** sw.c 2013-05-10 16:14:48.692299000 +0200
--- if.c 2013-05-10 16:15:03.496639000 +0200
***************
*** 471,482 ****
static int is_sb_offset(u64 offset)
{
! switch (offset) {
! case 65536:
! case 67108864:
! case 274877906944:
return 1;
- }
return 0;
}
--- 471,480 ----
static int is_sb_offset(u64 offset)
{
! if (offset == btrfs_sb_offset(0) ||
! offset == btrfs_sb_offset(1) ||
! offset == btrfs_sb_offset(2))
return 1;
return 0;
}
And this is the generated amd64 assembler code diff:
*** /tmp/sw 2013-05-10 15:57:49.096976480 +0200
--- /tmp/if 2013-05-10 16:00:41.712927262 +0200
***************
*** 1378,1397 ****
! 16c1: 49 81 fe 00 00 00 04 cmp $0x4000000,%r14
16c8: 74 20 je 16ea <flush_pending+0x305>
! 16ca: 48 b8 00 00 00 00 40 mov $0x4000000000,%rax
! 16d1: 00 00 00
! 16d4: 49 39 c6 cmp %rax,%r14
! 16d7: 74 11 je 16ea <flush_pending+0x305>
! 16d9: 8b 54 24 4c mov 0x4c(%rsp),%edx
! 16dd: 89 54 24 20 mov %edx,0x20(%rsp)
! 16e1: 49 81 fe 00 00 01 00 cmp $0x10000,%r14
16e8: 75 08 jne 16f2 <flush_pending+0x30d>
! 16ea: c7 44 24 20 00 10 00 movl $0x1000,0x20(%rsp)
16f1: 00
16f2: b9 00 00 00 00 mov $0x0,%ecx
! 16f7: 8b 54 24 20 mov 0x20(%rsp),%edx
--- 1378,1397 ----
! 16c1: 49 81 fe 00 00 01 00 cmp $0x10000,%r14
16c8: 74 20 je 16ea <flush_pending+0x305>
! 16ca: 49 81 fe 00 00 00 04 cmp $0x4000000,%r14
! 16d1: 74 17 je 16ea <flush_pending+0x305>
! 16d3: 8b 44 24 4c mov 0x4c(%rsp),%eax
! 16d7: 89 44 24 10 mov %eax,0x10(%rsp)
! 16db: 48 ba 00 00 00 00 40 mov $0x4000000000,%rdx
! 16e2: 00 00 00
! 16e5: 49 39 d6 cmp %rdx,%r14
16e8: 75 08 jne 16f2 <flush_pending+0x30d>
! 16ea: c7 44 24 10 00 10 00 movl $0x1000,0x10(%rsp)
16f1: 00
16f2: b9 00 00 00 00 mov $0x0,%ecx
! 16f7: 8b 54 24 10 mov 0x10(%rsp),%edx
--
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