Re: [PATCH] btrfs: fix chattr failing on nodatasum files that have the compress flag

[Qu Wenruo]

在 2026/10/10 21:24, Hengyu Liang 写道:
> Commit cf1afec09e9f ("btrfs: validate properties before setting them")
> made btrfs_set_prop() validate a property before setting it. For the
> compression property, the validation fails with -EINVAL when the inode
> has NODATASUM.
>
> However, a file created on a filesystem mounted with nodatasum has
> NODATASUM and still inherits the compress flag from its directory, and
> btrfs_fileattr_set() sets the compression property whenever the new
> flags include FS_COMPR_FL. As of now, chattr fails on such a file, even
> when it only changes another flag.
>
> The issue can be reproduced with:
>
>      mkfs.btrfs -f /dev/sdb
>      mount -o nodatasum /dev/sdb /mnt
>      mkdir /mnt/dir
>      chattr +c /mnt/dir
>      touch /mnt/dir/file
>      chattr +A /mnt/dir/file
>
> Before commit cf1afec09e9f ("btrfs: validate properties before setting
> them"), the last command succeeds.
>
> After that commit, it fails with EINVAL.

Explain the reason why it fails.

> This patch will make btrfs_fileattr_set() set the compression property
> only when the inode can be compressed.
>
> Fixes: cf1afec09e9f ("btrfs: validate properties before setting them")
> Cc: stable@xxxxxxxxxxxxxxx # 7.2+
> Signed-off-by: Hengyu Liang <hengyul@xxxxxxxxxx>
> ---
>   fs/btrfs/ioctl.c | 7 ++++++-
>   1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
> index 52aab510aea0..347509043f2e 100644
> --- a/fs/btrfs/ioctl.c
> +++ b/fs/btrfs/ioctl.c
> @@ -421,7 +421,12 @@ int btrfs_fileattr_set(struct mnt_idmap *idmap,
>   	if (IS_ERR(trans))
>   		return PTR_ERR(trans);
>   
> -	if (comp) {
> +	/*
> +	 * An inode with NODATASUM can not be compressed but can still have the
> +	 * compress flag, inherited from its parent directory. Setting the
> +	 * property fails validation for such an inode, so leave it unset.
> +	 */

This is very LLM-like, and very LLM's objective-oriented behavior.
Disclose it first.

Secondly it just slightly do nothing, which is not the expected behavior.

Furthermore, this introduced another layer of exceptions.

For regular mount options, -o nodatasum,compress, the later compress 
will override the nodatasum.

So when setting compress in the first place, the NODATASUM/NODATACOW 
flag should be cleared.

> +	if (comp && btrfs_inode_can_compress(inode)) {
>   		ret = btrfs_set_prop(trans, inode, "btrfs.compression",
>   				     comp, strlen(comp), 0);
>   		if (ret)