On 2017年07月28日 05:29, Jeff Mahoney wrote:
On 7/27/17 12:38 PM, Jeff Mahoney wrote:
On 7/26/17 9:35 PM, Qu Wenruo wrote:
On 2017年07月26日 04:54, jeffm@xxxxxxxx wrote:
From: Jeff Mahoney <jeffm@xxxxxxxx>
Commit 522ef705e38 (btrfs-progs: convert: Introduce function to calculate
the available space) changed how we handle migrating file data so that
we never have btrfs space associated with the reserved ranges. This
works pretty well and when we iterate over the file blocks, the
associations are redirected to the migrated locations.
This commit missed the case in block_iterate_proc where we just check
for intersection with a superblock location before looking up a block
group. intersect_with_sb checks to see if the range intersects with
a stripe containing a superblock but, in fact, we've reserved the
full 0-1MB range at the start of the disk. So a file block located
at e.g. 160kB will fall in the reserved region but won't be excepted
in block_iterate_block. We ultimately hit a BUG_ON when we fail
to look up the block group for that location.
The description of the problem is indeed correct.
This is reproducible using convert-tests/003-ext4-basic.
Thanks for pointing this out, I also reproduced it.
While it would be nicer if you could upload a special crafted image as
indicated test case.
IIRC the test passed without problem several versions ago, so there may
be some factors preventing the bug from being exposed.
The fix is to have intersect_with_sb and block_iterate_proc understand
the full size of the reserved ranges. Since we use the range to
determine the boundary for the block iterator, let's just return the
boundary. 0 isn't a valid boundary and means that we proceed normally
with block group lookup.
I'm OK with current fix as it indeed fix the bug and has minimal impact
on current code.
So feel free to add:
Reviewed-by: Qu Wenruo <quwenruo.btrfs@xxxxxxx>
While I think there is a better way to solve it more completely.
As when we run into block_iterate_proc(), we have already created
ext2_save/image.
So we can use the the image as ext2 <-> btrfs position mapping, just as
we have already done in record_file_blocks().
That's to say, we don't need too much care about the intersection with
reserved range, but just letting record_file_blocks() to handle it will
be good enough.
What do you think about this idea?
I think you're right. It should do the mapping already so we don't need
to do anything special in block_iterate_proc. I can test that in a bit.
So the idea works and, in fact, we could really get rid of most of
block_iterate_proc and still get correct results. This code is an
optimization so that we can quickly assemble larger extents and not have
to grow on-disk extents repeatedly. The code as it is does the right
thing most of the time but the boundary condition triggers the barrier
for every block in a migrated range and record_file_blocks must do the
growing. The end result works fine, it's just slower than it needs to
be for that 0-1MB range. I'm not sure I care enough to invest the time
to fix that.
Yes, the record_file_extent() handles the mapping in a slow way, by
doing btrfs_search_slot() to do the mapping, no matter if it's in the
reserved range.
So performance is much slower.
Performance wise, I'm OK using the current code.
Thanks,
Qu
-Jeff
-Jeff
Thanks,
Qu
Cc: Qu Wenruo <quwenruo.btrfs@xxxxxxx>
Signed-off-by: Jeff Mahoney <jeffm@xxxxxxxx>
---
convert/source-fs.c | 25 +++++++++++--------------
1 file changed, 11 insertions(+), 14 deletions(-)
diff --git a/convert/source-fs.c b/convert/source-fs.c
index 80e4e41..09f6995 100644
--- a/convert/source-fs.c
+++ b/convert/source-fs.c
@@ -28,18 +28,16 @@ const struct simple_range btrfs_reserved_ranges[3]
= {
{ BTRFS_SB_MIRROR_OFFSET(2), SZ_64K }
};
-static int intersect_with_sb(u64 bytenr, u64 num_bytes)
+static u64 intersect_with_reserved(u64 bytenr, u64 num_bytes)
{
int i;
- u64 offset;
- for (i = 0; i < BTRFS_SUPER_MIRROR_MAX; i++) {
- offset = btrfs_sb_offset(i);
- offset &= ~((u64)BTRFS_STRIPE_LEN - 1);
+ for (i = 0; i < ARRAY_SIZE(btrfs_reserved_ranges); i++) {
+ const struct simple_range *range = &btrfs_reserved_ranges[i];
- if (bytenr < offset + BTRFS_STRIPE_LEN &&
- bytenr + num_bytes > offset)
- return 1;
+ if (bytenr < range_end(range) &&
+ bytenr + num_bytes >= range->start)
+ return range_end(range);
}
return 0;
}
@@ -64,14 +62,14 @@ int block_iterate_proc(u64 disk_block, u64
file_block,
struct blk_iterate_data *idata)
{
int ret = 0;
- int sb_region;
+ u64 reserved_boundary;
int do_barrier;
struct btrfs_root *root = idata->root;
struct btrfs_block_group_cache *cache;
u64 bytenr = disk_block * root->sectorsize;
- sb_region = intersect_with_sb(bytenr, root->sectorsize);
- do_barrier = sb_region || disk_block >= idata->boundary;
+ reserved_boundary = intersect_with_reserved(bytenr,
root->sectorsize);
+ do_barrier = reserved_boundary || disk_block >= idata->boundary;
if ((idata->num_blocks > 0 && do_barrier) ||
(file_block > idata->first_block + idata->num_blocks) ||
(disk_block != idata->disk_block + idata->num_blocks)) {
@@ -91,9 +89,8 @@ int block_iterate_proc(u64 disk_block, u64 file_block,
goto fail;
}
- if (sb_region) {
- bytenr += BTRFS_STRIPE_LEN - 1;
- bytenr &= ~((u64)BTRFS_STRIPE_LEN - 1);
+ if (reserved_boundary) {
+ bytenr = reserved_boundary;
} else {
cache = btrfs_lookup_block_group(root->fs_info, bytenr);
BUG_ON(!cache);
--
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