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btrfs: fix check_shared for fiemap ioctl

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Only in the case of different root_id or different object_id, check_shared
identified extent as the shared. However, If a extent was referred by
different offset of same file, it should also be identified as shared.
In addition, check_shared's loop scale is at least n^3, so if a extent
has too many references, even causes soft hang up.

First, add all delayed_ref to the ref_tree and calculate the unqiue_refs,
if the unique_refs is greater than one, return BACKREF_FOUND_SHARED.
Then individually add the on-disk reference(inline/keyed) to the ref_tree
and calculate the unique_refs of the ref_tree to check if the unique_refs
is greater than one.Because once there are two references to return
SHARED, so the time complexity is close to the constant.

Reported-by: Tsutomu Itoh <t-itoh@jp.fujitsu.com>
Signed-off-by: Lu Fengqi <lufq.fnst@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Lu Fengqi 2016-06-13 09:36:46 +08:00 • committed by David Sterba
parent b0de6c4c81
commit afce772e87
2 changed files with 369 additions and 10 deletions
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18
fs/btrfs/extent_io.c
View file

@ -20,6 +20,7 @@
#include "locking.h"
#include "rcu-string.h"
#include "backref.h"
#include "transaction.h"
static struct kmem_cache *extent_state_cache;
static struct kmem_cache *extent_buffer_cache;
@ -4487,11 +4488,24 @@ int extent_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
flags |= (FIEMAP_EXTENT_DELALLOC |
FIEMAP_EXTENT_UNKNOWN);
} else if (fieinfo->fi_extents_max) {
struct btrfs_trans_handle *trans;
u64 bytenr = em->block_start -
(em->start - em->orig_start);
disko = em->block_start + offset_in_extent;
/*
* We need a trans handle to get delayed refs
*/
trans = btrfs_join_transaction(root);
/*
* It's OK if we can't start a trans we can still check
* from commit_root
*/
if (IS_ERR(trans))
trans = NULL;
/*
* As btrfs supports shared space, this information
* can be exported to userspace tools via
@ -4499,9 +4513,11 @@ int extent_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
* then we're just getting a count and we can skip the
* lookup stuff.
*/
ret = btrfs_check_shared(NULL, root->fs_info,
ret = btrfs_check_shared(trans, root->fs_info,
root->objectid,
btrfs_ino(inode), bytenr);
if (trans)
btrfs_end_transaction(trans, root);
if (ret < 0)
goto out_free;
if (ret)