Re: [PATCH 1/2] btrfs: inode: Don't compress if NODATASUM or NODATACOW set

[Qu Wenruo <quwenruo.btrfs@gmx.com>]

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Ping?

This patch should fix the problem of compressed extent even when
nodatasum is set.

It has been one year but we still didn't get a conclusion on where
force_compress should behave.

But at least to me, NODATASUM is a strong exclusion for compress, no
matter whatever option we use, we should NEVER compress data without
datasum/datacow.

So I still want to push this patch as is.

Thanks,
Qu


On 2018/5/15 下午3:36, 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.
> 
> Normally NODATACOW is detected properly in run_delalloc_range() so
> compression won't happen for NODATACOW.
> 
> However for NODATASUM we don't have any check, and it can cause
> compressed extent without csum pretty easily, just by:
> ------
> mkfs.btrfs -f $dev
> mount $dev $mnt -o nodatasum
> touch $mnt/foobar
> mount -o remount,datasum,compress $mnt
> xfs_io -f -c "pwrite 0 128K" $mnt/foobar
> ------
> 
> And in fact, we have bug report about corrupted compressed extent
> without proper data checksum so even RAID1 can't recover the corruption.
> (https://bugzilla.kernel.org/show_bug.cgi?id=199707)
> 
> Running compression without proper checksum could cause more damage when
> corruption happens, so there is no need to allow compression for
> NODATACSUM.
> 
> Reported-by: James Harvey <jamespharvey20@gmail.com>
> Signed-off-by: Qu Wenruo <wqu@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;
> +
>  	/* force compress */
>  	if (btrfs_test_opt(fs_info, FORCE_COMPRESS))
>  		return 1;
> 


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