[PATCH 1/2] btrfs: fix zstd compression parameter

[PATCH 1/2] btrfs: fix zstd compression parameter

[Anand Jain]

We let to pass zstd compression parameter even if its not fully written.
For example:
  btrfs prop set /btrfs compression zst
  btrfs prop get /btrfs compression
     compression=zst

zlib and lzo are fine.

Fix it by using the expected number of char in strncmp().

Signed-off-by: Anand Jain <anand.jain@oracle.com>
---
 fs/btrfs/props.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/btrfs/props.c b/fs/btrfs/props.c
index 8577ea1d4e2b..ef6502a94712 100644
--- a/fs/btrfs/props.c
+++ b/fs/btrfs/props.c
@@ -306,7 +306,7 @@ static int prop_compression_apply(struct inode *inode, const char *value,
 		btrfs_set_fs_incompat(fs_info, COMPRESS_LZO);
 	} else if (!strncmp("zlib", value, 4)) {
 		type = BTRFS_COMPRESS_ZLIB;
-	} else if (!strncmp("zstd", value, len)) {
+	} else if (!strncmp("zstd", value, 4)) {
 		type = BTRFS_COMPRESS_ZSTD;
 		btrfs_set_fs_incompat(fs_info, COMPRESS_ZSTD);
 	} else {
-- 
1.8.3.1

[PATCH 2/2] btrfs: fix vanished compression property after failed set

[Anand Jain]

The compression property resets to NULL, instead of the old value if we
fail to set the new compression parameter.

btrfs prop get /btrfs compression
  compression=lzo
btrfs prop set /btrfs compression zli
  ERROR: failed to set compression for /btrfs: Invalid argument
btrfs prop get /btrfs compression

This is because the compression property ->validate() is successful for
'zli' as the strncmp() used the len passed from the userland.

Fix it by using the expected string length in strncmp().

Signed-off-by: Anand Jain <anand.jain@oracle.com>
---
 fs/btrfs/props.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/fs/btrfs/props.c b/fs/btrfs/props.c
index ef6502a94712..7aa362c2fbcf 100644
--- a/fs/btrfs/props.c
+++ b/fs/btrfs/props.c
@@ -277,11 +277,11 @@ static int prop_compression_validate(struct inode *inode, const char *value,
 	if (!value)
 		return 0;
 
-	if (!strncmp("lzo", value, len))
+	if (!strncmp("lzo", value, 3))
 		return 0;
-	else if (!strncmp("zlib", value, len))
+	else if (!strncmp("zlib", value, 4))
 		return 0;
-	else if (!strncmp("zstd", value, len))
+	else if (!strncmp("zstd", value, 4))
 		return 0;
 
 	return -EINVAL;
-- 
1.8.3.1

Re: [PATCH 1/2] btrfs: fix zstd compression parameter

[Nikolay Borisov]

On 13.03.19 г. 7:36 ч., Anand Jain wrote:
> We let to pass zstd compression parameter even if its not fully written.
> For example:
>   btrfs prop set /btrfs compression zst
>   btrfs prop get /btrfs compression
>      compression=zst
> 
> zlib and lzo are fine.
> 
> Fix it by using the expected number of char in strncmp().
> 
> Signed-off-by: Anand Jain <anand.jain@oracle.com>

Reviewed-by: Nikolay Borisov <nborisov@suse.com>

> ---
>  fs/btrfs/props.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/btrfs/props.c b/fs/btrfs/props.c
> index 8577ea1d4e2b..ef6502a94712 100644
> --- a/fs/btrfs/props.c
> +++ b/fs/btrfs/props.c
> @@ -306,7 +306,7 @@ static int prop_compression_apply(struct inode *inode, const char *value,
>  		btrfs_set_fs_incompat(fs_info, COMPRESS_LZO);
>  	} else if (!strncmp("zlib", value, 4)) {
>  		type = BTRFS_COMPRESS_ZLIB;
> -	} else if (!strncmp("zstd", value, len)) {
> +	} else if (!strncmp("zstd", value, 4)) {
>  		type = BTRFS_COMPRESS_ZSTD;
>  		btrfs_set_fs_incompat(fs_info, COMPRESS_ZSTD);
>  	} else {
> 

Re: [PATCH 2/2] btrfs: fix vanished compression property after failed set

[Nikolay Borisov]

On 13.03.19 г. 7:36 ч., Anand Jain wrote:
> The compression property resets to NULL, instead of the old value if we
> fail to set the new compression parameter.
> 
> btrfs prop get /btrfs compression
>   compression=lzo
> btrfs prop set /btrfs compression zli
>   ERROR: failed to set compression for /btrfs: Invalid argument
> btrfs prop get /btrfs compression
> 
> This is because the compression property ->validate() is successful for
> 'zli' as the strncmp() used the len passed from the userland.
> 
> Fix it by using the expected string length in strncmp().
> 
> Signed-off-by: Anand Jain <anand.jain@oracle.com>
> ---
>  fs/btrfs/props.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/btrfs/props.c b/fs/btrfs/props.c
> index ef6502a94712..7aa362c2fbcf 100644
> --- a/fs/btrfs/props.c
> +++ b/fs/btrfs/props.c
> @@ -277,11 +277,11 @@ static int prop_compression_validate(struct inode *inode, const char *value,
>  	if (!value)
>  		return 0;
>  
> -	if (!strncmp("lzo", value, len))
> +	if (!strncmp("lzo", value, 3))
>  		return 0;
> -	else if (!strncmp("zlib", value, len))
> +	else if (!strncmp("zlib", value, 4))
>  		return 0;
> -	else if (!strncmp("zstd", value, len))
> +	else if (!strncmp("zstd", value, 4))
>  		return 0;

This also makes the len argument to prop_compression_validate redundant
and should be removed as well.

>  
>  	return -EINVAL;
> 

Re: [PATCH 2/2] btrfs: fix vanished compression property after failed set

[Nikolay Borisov]

On 13.03.19 г. 9:20 ч., Nikolay Borisov wrote:
> 
> 
> On 13.03.19 г. 7:36 ч., Anand Jain wrote:
>> The compression property resets to NULL, instead of the old value if we
>> fail to set the new compression parameter.
>>
>> btrfs prop get /btrfs compression
>>   compression=lzo
>> btrfs prop set /btrfs compression zli
>>   ERROR: failed to set compression for /btrfs: Invalid argument
>> btrfs prop get /btrfs compression
>>
>> This is because the compression property ->validate() is successful for
>> 'zli' as the strncmp() used the len passed from the userland.
>>
>> Fix it by using the expected string length in strncmp().
>>
>> Signed-off-by: Anand Jain <anand.jain@oracle.com>
>> ---
>>  fs/btrfs/props.c | 6 +++---
>>  1 file changed, 3 insertions(+), 3 deletions(-)
>>
>> diff --git a/fs/btrfs/props.c b/fs/btrfs/props.c
>> index ef6502a94712..7aa362c2fbcf 100644
>> --- a/fs/btrfs/props.c
>> +++ b/fs/btrfs/props.c
>> @@ -277,11 +277,11 @@ static int prop_compression_validate(struct inode *inode, const char *value,
>>  	if (!value)
>>  		return 0;
>>  
>> -	if (!strncmp("lzo", value, len))
>> +	if (!strncmp("lzo", value, 3))
>>  		return 0;
>> -	else if (!strncmp("zlib", value, len))
>> +	else if (!strncmp("zlib", value, 4))
>>  		return 0;
>> -	else if (!strncmp("zstd", value, len))
>> +	else if (!strncmp("zstd", value, 4))
>>  		return 0;
> 
> This also makes the len argument to prop_compression_validate redundant
> and should be removed as well.


As a matter of fact I don't see any value in prop_compression_validate
since the exact same code is used in prop_compression_apply and einval
will be returned if an invalid value is passed in.

> 
>>  
>>  	return -EINVAL;
>>
> 

Re: [PATCH 2/2] btrfs: fix vanished compression property after failed set

[Anand Jain]

On 3/13/19 3:22 PM, Nikolay Borisov wrote:
> 
> 
> On 13.03.19 г. 9:20 ч., Nikolay Borisov wrote:
>>
>>
>> On 13.03.19 г. 7:36 ч., Anand Jain wrote:
>>> The compression property resets to NULL, instead of the old value if we
>>> fail to set the new compression parameter.
>>>
>>> btrfs prop get /btrfs compression
>>>    compression=lzo
>>> btrfs prop set /btrfs compression zli
>>>    ERROR: failed to set compression for /btrfs: Invalid argument
>>> btrfs prop get /btrfs compression
>>>
>>> This is because the compression property ->validate() is successful for
>>> 'zli' as the strncmp() used the len passed from the userland.
>>>
>>> Fix it by using the expected string length in strncmp().
>>>
>>> Signed-off-by: Anand Jain <anand.jain@oracle.com>
>>> ---
>>>   fs/btrfs/props.c | 6 +++---
>>>   1 file changed, 3 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/fs/btrfs/props.c b/fs/btrfs/props.c
>>> index ef6502a94712..7aa362c2fbcf 100644
>>> --- a/fs/btrfs/props.c
>>> +++ b/fs/btrfs/props.c
>>> @@ -277,11 +277,11 @@ static int prop_compression_validate(struct inode *inode, const char *value,
>>>   	if (!value)
>>>   		return 0;
>>>   
>>> -	if (!strncmp("lzo", value, len))
>>> +	if (!strncmp("lzo", value, 3))
>>>   		return 0;
>>> -	else if (!strncmp("zlib", value, len))
>>> +	else if (!strncmp("zlib", value, 4))
>>>   		return 0;
>>> -	else if (!strncmp("zstd", value, len))
>>> +	else if (!strncmp("zstd", value, 4))
>>>   		return 0;
>>
>> This also makes the len argument to prop_compression_validate redundant
>> and should be removed as well.

  Its part of the 'struct prop_handler', its better to keep it until
  properties have completely evolved.

> 
> As a matter of fact I don't see any value in prop_compression_validate
> since the exact same code is used in prop_compression_apply and einval
> will be returned if an invalid value is passed in.

  I notice too. But its better to keep it until the most of the
  properties have evolved.

  As of now btrfs_set_prop() follows sequence..
    h->validate(prop)
    setxattr(prop)
    h->apply(prop)

  If validate fails its easy to fail exit.

Thanks, Anand


>>
>>>   
>>>   	return -EINVAL;
>>>
>>

Re: [PATCH 2/2] btrfs: fix vanished compression property after failed set

[Anand Jain]

On 3/13/19 1:36 PM, Anand Jain wrote:
> The compression property resets to NULL, instead of the old value if we
> fail to set the new compression parameter.
> 
> btrfs prop get /btrfs compression
>    compression=lzo
> btrfs prop set /btrfs compression zli
>    ERROR: failed to set compression for /btrfs: Invalid argument
> btrfs prop get /btrfs compression
> 
> This is because the compression property ->validate() is successful for
> 'zli' as the strncmp() used the len passed from the userland.
> 
> Fix it by using the expected string length in strncmp().
> 
> Signed-off-by: Anand Jain <anand.jain@oracle.com>
> ---
>   fs/btrfs/props.c | 6 +++---
>   1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/btrfs/props.c b/fs/btrfs/props.c
> index ef6502a94712..7aa362c2fbcf 100644
> --- a/fs/btrfs/props.c
> +++ b/fs/btrfs/props.c
> @@ -277,11 +277,11 @@ static int prop_compression_validate(struct inode *inode, const char *value,
>   	if (!value)
>   		return 0;
>   
> -	if (!strncmp("lzo", value, len))
> +	if (!strncmp("lzo", value, 3))
>   		return 0;
> -	else if (!strncmp("zlib", value, len))
> +	else if (!strncmp("zlib", value, 4))
>   		return 0;
> -	else if (!strncmp("zstd", value, len))
> +	else if (!strncmp("zstd", value, 4))
>   		return 0;
>


   Nack.
Now some junk value after expected string is not an error.
such as..

btrfs prop set /btrfs compression lzo110

Thanks, Anand

>   	return -EINVAL;
> 

Re: [PATCH 2/2] btrfs: fix vanished compression property after failed set

[Anand Jain]

On 3/13/19 6:33 PM, Anand Jain wrote:
> 
> 
> 
> On 3/13/19 1:36 PM, Anand Jain wrote:
>> The compression property resets to NULL, instead of the old value if we
>> fail to set the new compression parameter.
>>
>> btrfs prop get /btrfs compression
>>    compression=lzo
>> btrfs prop set /btrfs compression zli
>>    ERROR: failed to set compression for /btrfs: Invalid argument
>> btrfs prop get /btrfs compression
>>
>> This is because the compression property ->validate() is successful for
>> 'zli' as the strncmp() used the len passed from the userland.
>>
>> Fix it by using the expected string length in strncmp().
>>
>> Signed-off-by: Anand Jain <anand.jain@oracle.com>
>> ---
>>   fs/btrfs/props.c | 6 +++---
>>   1 file changed, 3 insertions(+), 3 deletions(-)
>>
>> diff --git a/fs/btrfs/props.c b/fs/btrfs/props.c
>> index ef6502a94712..7aa362c2fbcf 100644
>> --- a/fs/btrfs/props.c
>> +++ b/fs/btrfs/props.c
>> @@ -277,11 +277,11 @@ static int prop_compression_validate(struct 
>> inode *inode, const char *value,
>>       if (!value)
>>           return 0;
>> -    if (!strncmp("lzo", value, len))
>> +    if (!strncmp("lzo", value, 3))
>>           return 0;
>> -    else if (!strncmp("zlib", value, len))
>> +    else if (!strncmp("zlib", value, 4))
>>           return 0;
>> -    else if (!strncmp("zstd", value, len))
>> +    else if (!strncmp("zstd", value, 4))
>>           return 0;
>>
> 
> 
>    Nack.
> Now some junk value after expected string is not an error.
> such as..
> 
> btrfs prop set /btrfs compression lzo110

  mount(8) compression and the property compression parameter have
  diverged, the compression levels are set able only from
  mount(8) option? We should rather make it consistent?

Thanks, Anand


> Thanks, Anand
> 
>>       return -EINVAL;
>>

Re: [PATCH 2/2] btrfs: fix vanished compression property after failed set

[David Sterba]

On Wed, Mar 13, 2019 at 04:49:54PM +0800, Anand Jain wrote:
> 
> 
> On 3/13/19 3:22 PM, Nikolay Borisov wrote:
> > 
> > 
> > On 13.03.19 г. 9:20 ч., Nikolay Borisov wrote:
> >>
> >>
> >> On 13.03.19 г. 7:36 ч., Anand Jain wrote:
> >>> The compression property resets to NULL, instead of the old value if we
> >>> fail to set the new compression parameter.
> >>>
> >>> btrfs prop get /btrfs compression
> >>>    compression=lzo
> >>> btrfs prop set /btrfs compression zli
> >>>    ERROR: failed to set compression for /btrfs: Invalid argument
> >>> btrfs prop get /btrfs compression
> >>>
> >>> This is because the compression property ->validate() is successful for
> >>> 'zli' as the strncmp() used the len passed from the userland.
> >>>
> >>> Fix it by using the expected string length in strncmp().
> >>>
> >>> Signed-off-by: Anand Jain <anand.jain@oracle.com>
> >>> ---
> >>>   fs/btrfs/props.c | 6 +++---
> >>>   1 file changed, 3 insertions(+), 3 deletions(-)
> >>>
> >>> diff --git a/fs/btrfs/props.c b/fs/btrfs/props.c
> >>> index ef6502a94712..7aa362c2fbcf 100644
> >>> --- a/fs/btrfs/props.c
> >>> +++ b/fs/btrfs/props.c
> >>> @@ -277,11 +277,11 @@ static int prop_compression_validate(struct inode *inode, const char *value,
> >>>   	if (!value)
> >>>   		return 0;
> >>>   
> >>> -	if (!strncmp("lzo", value, len))
> >>> +	if (!strncmp("lzo", value, 3))
> >>>   		return 0;
> >>> -	else if (!strncmp("zlib", value, len))
> >>> +	else if (!strncmp("zlib", value, 4))
> >>>   		return 0;
> >>> -	else if (!strncmp("zstd", value, len))
> >>> +	else if (!strncmp("zstd", value, 4))
> >>>   		return 0;
> >>
> >> This also makes the len argument to prop_compression_validate redundant
> >> and should be removed as well.
> 
>   Its part of the 'struct prop_handler', its better to keep it until
>   properties have completely evolved.
> 
> > 
> > As a matter of fact I don't see any value in prop_compression_validate
> > since the exact same code is used in prop_compression_apply and einval
> > will be returned if an invalid value is passed in.
> 
>   I notice too. But its better to keep it until the most of the
>   properties have evolved.
> 
>   As of now btrfs_set_prop() follows sequence..
>     h->validate(prop)
>     setxattr(prop)
>     h->apply(prop)
> 
>   If validate fails its easy to fail exit.

Agreed, some code could be repeated in the apply() callback, but
otherwise I'd like to keep both.

Re: [PATCH 2/2] btrfs: fix vanished compression property after failed set

[David Sterba]

On Wed, Mar 13, 2019 at 06:49:27PM +0800, Anand Jain wrote:
> 
> 
> On 3/13/19 6:33 PM, Anand Jain wrote:
> > 
> > 
> > 
> > On 3/13/19 1:36 PM, Anand Jain wrote:
> >> The compression property resets to NULL, instead of the old value if we
> >> fail to set the new compression parameter.
> >>
> >> btrfs prop get /btrfs compression
> >>    compression=lzo
> >> btrfs prop set /btrfs compression zli
> >>    ERROR: failed to set compression for /btrfs: Invalid argument
> >> btrfs prop get /btrfs compression
> >>
> >> This is because the compression property ->validate() is successful for
> >> 'zli' as the strncmp() used the len passed from the userland.
> >>
> >> Fix it by using the expected string length in strncmp().
> >>
> >> Signed-off-by: Anand Jain <anand.jain@oracle.com>
> >> ---
> >>   fs/btrfs/props.c | 6 +++---
> >>   1 file changed, 3 insertions(+), 3 deletions(-)
> >>
> >> diff --git a/fs/btrfs/props.c b/fs/btrfs/props.c
> >> index ef6502a94712..7aa362c2fbcf 100644
> >> --- a/fs/btrfs/props.c
> >> +++ b/fs/btrfs/props.c
> >> @@ -277,11 +277,11 @@ static int prop_compression_validate(struct 
> >> inode *inode, const char *value,
> >>       if (!value)
> >>           return 0;
> >> -    if (!strncmp("lzo", value, len))
> >> +    if (!strncmp("lzo", value, 3))
> >>           return 0;
> >> -    else if (!strncmp("zlib", value, len))
> >> +    else if (!strncmp("zlib", value, 4))
> >>           return 0;
> >> -    else if (!strncmp("zstd", value, len))
> >> +    else if (!strncmp("zstd", value, 4))
> >>           return 0;
> >>
> > 
> > 
> >    Nack.
> > Now some junk value after expected string is not an error.
> > such as..
> > 
> > btrfs prop set /btrfs compression lzo110
> 
>   mount(8) compression and the property compression parameter have
>   diverged, the compression levels are set able only from
>   mount(8) option? We should rather make it consistent?

Yes the properties should be able to get to the same result as the mount
option, but this needs more changes as the level is not extracted from
the property and passed to the compression (in compress_file_range).

Re: [PATCH 2/2] btrfs: fix vanished compression property after failed set

[David Sterba]

On Wed, Mar 13, 2019 at 06:33:50PM +0800, Anand Jain wrote:
> 
> 
> 
> On 3/13/19 1:36 PM, Anand Jain wrote:
> > The compression property resets to NULL, instead of the old value if we
> > fail to set the new compression parameter.
> > 
> > btrfs prop get /btrfs compression
> >    compression=lzo
> > btrfs prop set /btrfs compression zli
> >    ERROR: failed to set compression for /btrfs: Invalid argument
> > btrfs prop get /btrfs compression
> > 
> > This is because the compression property ->validate() is successful for
> > 'zli' as the strncmp() used the len passed from the userland.
> > 
> > Fix it by using the expected string length in strncmp().
> > 
> > Signed-off-by: Anand Jain <anand.jain@oracle.com>
> > ---
> >   fs/btrfs/props.c | 6 +++---
> >   1 file changed, 3 insertions(+), 3 deletions(-)
> > 
> > diff --git a/fs/btrfs/props.c b/fs/btrfs/props.c
> > index ef6502a94712..7aa362c2fbcf 100644
> > --- a/fs/btrfs/props.c
> > +++ b/fs/btrfs/props.c
> > @@ -277,11 +277,11 @@ static int prop_compression_validate(struct inode *inode, const char *value,
> >   	if (!value)
> >   		return 0;
> >   
> > -	if (!strncmp("lzo", value, len))
> > +	if (!strncmp("lzo", value, 3))
> >   		return 0;
> > -	else if (!strncmp("zlib", value, len))
> > +	else if (!strncmp("zlib", value, 4))
> >   		return 0;
> > -	else if (!strncmp("zstd", value, len))
> > +	else if (!strncmp("zstd", value, 4))
> >   		return 0;
> >
> 
> 
>    Nack.
> Now some junk value after expected string is not an error.
> such as..
> 
> btrfs prop set /btrfs compression lzo110

This was intentional when the zlib levels were introduced so older
kernels can understand newer compression specifier but still have a sane
fallback (ie use the default level). Now it would be better to extend
the validation to parse the method:level format at least. But as
mentioned in the other mail, the level needs to be propagated elsewhere
too so it's not just a change to the validation.

Re: [PATCH 2/2] btrfs: fix vanished compression property after failed set

[Anand Jain]

On 3/14/19 1:45 AM, David Sterba wrote:
> On Wed, Mar 13, 2019 at 06:33:50PM +0800, Anand Jain wrote:
>>
>>
>>
>> On 3/13/19 1:36 PM, Anand Jain wrote:
>>> The compression property resets to NULL, instead of the old value if we
>>> fail to set the new compression parameter.
>>>
>>> btrfs prop get /btrfs compression
>>>     compression=lzo
>>> btrfs prop set /btrfs compression zli
>>>     ERROR: failed to set compression for /btrfs: Invalid argument
>>> btrfs prop get /btrfs compression
>>>
>>> This is because the compression property ->validate() is successful for
>>> 'zli' as the strncmp() used the len passed from the userland.
>>>
>>> Fix it by using the expected string length in strncmp().
>>>
>>> Signed-off-by: Anand Jain <anand.jain@oracle.com>
>>> ---
>>>    fs/btrfs/props.c | 6 +++---
>>>    1 file changed, 3 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/fs/btrfs/props.c b/fs/btrfs/props.c
>>> index ef6502a94712..7aa362c2fbcf 100644
>>> --- a/fs/btrfs/props.c
>>> +++ b/fs/btrfs/props.c
>>> @@ -277,11 +277,11 @@ static int prop_compression_validate(struct inode *inode, const char *value,
>>>    	if (!value)
>>>    		return 0;
>>>    
>>> -	if (!strncmp("lzo", value, len))
>>> +	if (!strncmp("lzo", value, 3))
>>>    		return 0;
>>> -	else if (!strncmp("zlib", value, len))
>>> +	else if (!strncmp("zlib", value, 4))
>>>    		return 0;
>>> -	else if (!strncmp("zstd", value, len))
>>> +	else if (!strncmp("zstd", value, 4))
>>>    		return 0;
>>>
>>
>>
>>     Nack.
>> Now some junk value after expected string is not an error.
>> such as..
>>
>> btrfs prop set /btrfs compression lzo110
> 
> This was intentional when the zlib levels were introduced so older
> kernels can understand newer compression specifier but still have a sane
> fallback (ie use the default level). Now it would be better to extend
> the validation to parse the method:level format at least. But as
> mentioned in the other mail, the level needs to be propagated elsewhere
> too so it's not just a change to the validation.
> 

  Compression levels properties can be implemented in a newer set of the
  patches? So I believe this set ok to merge.

  The other way to fix this was to save and rewrite the old parameter,
  but that's not a good idea as well, because when parameter is not valid
  we should rather fail without any update (generation/transid should
  also remain unchanged, there is a bug [1] in the original code which
  shall be fixed separately).

  [1]
  with this patch,
  btrfs in dump-super /dev/sdb | grep "^generation"; btrfs prop set 
/btrfs compression zli; sync; btrfs in dump-super /dev/sdb | grep 
"^generation"

generation		21
ERROR: failed to set compression for /btrfs: Invalid argument
generation		22


Thanks, Anand