On 2018年05月15日 00:52, David Sterba wrote: > On Mon, May 14, 2018 at 03:02:10PM +0800, Qu Wenruo wrote: >> As btrfs(5) specified: >> >> Note >> If nodatacow or nodatasum are enabled, compression is disabled. >> >> If NODATASUM or NODATACOW set, we should not compress the extent. >> >> And in fact, we have bug report about corrupted compressed extent >> leading to memory corruption in mail list. > > Link please. > >> Although it's mostly buggy lzo implementation causing the problem, btrfs >> still needs to be fixed to meet the specification. > > That's very vague, what's the LZO bug? If the input is garbage and lzo > decompression cannot decompress it, it's not a lzo bug.
Still digging.
Would update this content in next version.
>
>> Reported-by: James Harvey <jamespharve...@gmail.com>
>> Signed-off-by: Qu Wenruo <w...@suse.com>
>> ---
>> fs/btrfs/inode.c | 8 ++++++++
>> 1 file changed, 8 insertions(+)
>>
>> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
>> index d241285a0d2a..dbef3f404559 100644
>> --- a/fs/btrfs/inode.c
>> +++ b/fs/btrfs/inode.c
>> @@ -396,6 +396,14 @@ static inline int inode_need_compress(struct inode
>> *inode, u64 start, u64 end)
>> {
>> struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
>>
>> + /*
>> + * Btrfs doesn't support compression without csum or CoW.
>> + * This should have the highest priority.
>> + */
>> + if (BTRFS_I(inode)->flags & BTRFS_INODE_NODATACOW ||
>> + BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM)
>> + return 0;
>
> This is also the wrong place to fix that, NODATASUM or NODATACOW inode
> should never make it to compress_file_range (that calls
> inode_need_compress).
Nope, in run_delalloc_range(), we calls inode_need_compress() to
determine if we goes to normal cow routine or goes to async routine
(compression).
So inode_need_compress() looks like a pretty valid location.
Just mount with nodatasum and create an inode, then remount to
datasum,compress, write something to that inode, you could hit the behavior.
Thanks,
Qu
>
>> +
>> /* force compress */
>> if (btrfs_test_opt(fs_info, FORCE_COMPRESS))
>> return 1;
>> --
>> 2.17.0
>>
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