btrfs: Use right extent length when inserting overlap extent map.

When current btrfs finds that a new extent map is going to be insereted
but failed with -EEXIST, it will try again to insert the extent map
but with the length of sectorsize.
This is OK if we don't enable 'no-holes' feature since all extent space
is continuous, we will not go into the not found->insert routine.

But if we enable 'no-holes' feature, it will make things out of control.
e.g. in 4K sectorsize, we pass the following args to btrfs_get_extent():
btrfs_get_extent() args: start:  27874 len 4100
28672		  27874		28672	27874+4100	32768
                    |-----------------------|
|---------hole--------------------|---------data----------|

1) not found and insert
Since no extent map containing the range, btrfs_get_extent() will go
into the not_found and insert routine, which will try to insert the
extent map (27874, 27847 + 4100).

2) first overlap
But it overlaps with (28672, 32768) extent, so -EEXIST will be returned
by add_extent_mapping().

3) retry but still overlap
After catching the -EEXIST, then btrfs_get_extent() will try insert it
again but with 4K length, which still overlaps, so -EEXIST will be
returned.

This makes the following patch fail to punch hole.
d77815461f047e561f77a07754ae923ade597d4e btrfs: Avoid trucating page or punching hole in a already existed hole.

This patch will use the right length, which is the (exsisting->start -
em->start) to insert, making the above patch works in 'no-holes' mode.
Also, some small code style problems in above patch is fixed too.

Reported-by: Filipe David Manana <fdmanana@gmail.com>
Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
Reviewed-by: Filipe David Manana <fdmanana@suse.com>
Tested-by: Filipe David Manana <fdmanana@suse.com>
Signed-off-by: Chris Mason <clm@fb.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 77e33534..f15c13f 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -2215,7 +2215,7 @@ static int btrfs_punch_hole(struct inode *inode, loff_t offset, loff_t len)
 		goto out_only_mutex;
 	}
 
-	lockstart = round_up(offset , BTRFS_I(inode)->root->sectorsize);
+	lockstart = round_up(offset, BTRFS_I(inode)->root->sectorsize);
 	lockend = round_down(offset + len,
 			     BTRFS_I(inode)->root->sectorsize) - 1;
 	same_page = ((offset >> PAGE_CACHE_SHIFT) ==
@@ -2276,7 +2276,7 @@ static int btrfs_punch_hole(struct inode *inode, loff_t offset, loff_t len)
 						tail_start + tail_len, 0, 1);
 				if (ret)
 					goto out_only_mutex;
-				}
+			}
 		}
 	}