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Subject[PATCH 5.4 09/32] btrfs: backref, only collect file extent items matching backref offset
Date
From: ethanwu <ethanwu@synology.com>

commit 7ac8b88ee668a5b4743ebf3e9888fabac85c334a upstream.

When resolving one backref of type EXTENT_DATA_REF, we collect all
references that simply reference the EXTENT_ITEM even though their
(file_pos - file_extent_item::offset) are not the same as the
btrfs_extent_data_ref::offset we are searching for.

This patch adds additional check so that we only collect references whose
(file_pos - file_extent_item::offset) == btrfs_extent_data_ref::offset.

Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: ethanwu <ethanwu@synology.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/btrfs/backref.c | 63 +++++++++++++++++++++++++++--------------------------
1 file changed, 33 insertions(+), 30 deletions(-)

--- a/fs/btrfs/backref.c
+++ b/fs/btrfs/backref.c
@@ -347,33 +347,10 @@ static int add_prelim_ref(const struct b
return -ENOMEM;

ref->root_id = root_id;
- if (key) {
+ if (key)
ref->key_for_search = *key;
- /*
- * We can often find data backrefs with an offset that is too
- * large (>= LLONG_MAX, maximum allowed file offset) due to
- * underflows when subtracting a file's offset with the data
- * offset of its corresponding extent data item. This can
- * happen for example in the clone ioctl.
- * So if we detect such case we set the search key's offset to
- * zero to make sure we will find the matching file extent item
- * at add_all_parents(), otherwise we will miss it because the
- * offset taken form the backref is much larger then the offset
- * of the file extent item. This can make us scan a very large
- * number of file extent items, but at least it will not make
- * us miss any.
- * This is an ugly workaround for a behaviour that should have
- * never existed, but it does and a fix for the clone ioctl
- * would touch a lot of places, cause backwards incompatibility
- * and would not fix the problem for extents cloned with older
- * kernels.
- */
- if (ref->key_for_search.type == BTRFS_EXTENT_DATA_KEY &&
- ref->key_for_search.offset >= LLONG_MAX)
- ref->key_for_search.offset = 0;
- } else {
+ else
memset(&ref->key_for_search, 0, sizeof(ref->key_for_search));
- }

ref->inode_list = NULL;
ref->level = level;
@@ -424,6 +401,7 @@ static int add_all_parents(struct btrfs_
u64 disk_byte;
u64 wanted_disk_byte = ref->wanted_disk_byte;
u64 count = 0;
+ u64 data_offset;

if (level != 0) {
eb = path->nodes[level];
@@ -457,11 +435,15 @@ static int add_all_parents(struct btrfs_

fi = btrfs_item_ptr(eb, slot, struct btrfs_file_extent_item);
disk_byte = btrfs_file_extent_disk_bytenr(eb, fi);
+ data_offset = btrfs_file_extent_offset(eb, fi);

if (disk_byte == wanted_disk_byte) {
eie = NULL;
old = NULL;
- count++;
+ if (ref->key_for_search.offset == key.offset - data_offset)
+ count++;
+ else
+ goto next;
if (extent_item_pos) {
ret = check_extent_in_eb(&key, eb, fi,
*extent_item_pos,
@@ -513,6 +495,7 @@ static int resolve_indirect_ref(struct b
int root_level;
int level = ref->level;
int index;
+ struct btrfs_key search_key = ref->key_for_search;

root_key.objectid = ref->root_id;
root_key.type = BTRFS_ROOT_ITEM_KEY;
@@ -545,13 +528,33 @@ static int resolve_indirect_ref(struct b
goto out;
}

+ /*
+ * We can often find data backrefs with an offset that is too large
+ * (>= LLONG_MAX, maximum allowed file offset) due to underflows when
+ * subtracting a file's offset with the data offset of its
+ * corresponding extent data item. This can happen for example in the
+ * clone ioctl.
+ *
+ * So if we detect such case we set the search key's offset to zero to
+ * make sure we will find the matching file extent item at
+ * add_all_parents(), otherwise we will miss it because the offset
+ * taken form the backref is much larger then the offset of the file
+ * extent item. This can make us scan a very large number of file
+ * extent items, but at least it will not make us miss any.
+ *
+ * This is an ugly workaround for a behaviour that should have never
+ * existed, but it does and a fix for the clone ioctl would touch a lot
+ * of places, cause backwards incompatibility and would not fix the
+ * problem for extents cloned with older kernels.
+ */
+ if (search_key.type == BTRFS_EXTENT_DATA_KEY &&
+ search_key.offset >= LLONG_MAX)
+ search_key.offset = 0;
path->lowest_level = level;
if (time_seq == SEQ_LAST)
- ret = btrfs_search_slot(NULL, root, &ref->key_for_search, path,
- 0, 0);
+ ret = btrfs_search_slot(NULL, root, &search_key, path, 0, 0);
else
- ret = btrfs_search_old_slot(root, &ref->key_for_search, path,
- time_seq);
+ ret = btrfs_search_old_slot(root, &search_key, path, time_seq);

/* root node has been locked, we can release @subvol_srcu safely here */
srcu_read_unlock(&fs_info->subvol_srcu, index);

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