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* [PATCH] bcache: fix wrong BITMASK offset value for BDEV_CACHE_MODE
@ 2021-07-20 10:32 Lin Feng
  2022-05-13 15:20 ` Coly Li
  0 siblings, 1 reply; 3+ messages in thread
From: Lin Feng @ 2021-07-20 10:32 UTC (permalink / raw)
  To: colyli; +Cc: axboe, linf, linux-kernel, linux-bcache

Original codes:
BITMASK(CACHE_SYNC,			struct cache_sb, flags, 0, 1);
BITMASK(CACHE_DISCARD,			struct cache_sb, flags, 1, 1);
BITMASK(CACHE_REPLACEMENT,		struct cache_sb, flags, 2, 3);
...
BITMASK(BDEV_CACHE_MODE,		struct cache_sb, flags, 0, 4);

Should BDEV_CACHE_MODE bits start from bit-nr 5(2+3) else it overlaps
with previous defined bit chunks, since we have 4 types of cache modes,
BDEV_CACHE_MODE will overwrite CACHE_SYNC and CACHE_DISCARD bits.

This bug stays there since first upstream version of bcache, don't know
why it lives so long, or am i missing something, please point me out
if I'm wrong, thanks!

Signed-off-by: Lin Feng <linf@wangsu.com>
---
 include/uapi/linux/bcache.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/uapi/linux/bcache.h b/include/uapi/linux/bcache.h
index cf7399f03b71..dccd89756451 100644
--- a/include/uapi/linux/bcache.h
+++ b/include/uapi/linux/bcache.h
@@ -288,7 +288,7 @@ BITMASK(CACHE_REPLACEMENT,		struct cache_sb, flags, 2, 3);
 #define CACHE_REPLACEMENT_FIFO		1U
 #define CACHE_REPLACEMENT_RANDOM	2U
 
-BITMASK(BDEV_CACHE_MODE,		struct cache_sb, flags, 0, 4);
+BITMASK(BDEV_CACHE_MODE,		struct cache_sb, flags, 5, 4);
 #define CACHE_MODE_WRITETHROUGH		0U
 #define CACHE_MODE_WRITEBACK		1U
 #define CACHE_MODE_WRITEAROUND		2U
-- 
2.31.1


^ permalink raw reply related	[flat|nested] 3+ messages in thread

* Re: [PATCH] bcache: fix wrong BITMASK offset value for BDEV_CACHE_MODE
  2021-07-20 10:32 [PATCH] bcache: fix wrong BITMASK offset value for BDEV_CACHE_MODE Lin Feng
@ 2022-05-13 15:20 ` Coly Li
  2022-05-16  1:50   ` Lin Feng
  0 siblings, 1 reply; 3+ messages in thread
From: Coly Li @ 2022-05-13 15:20 UTC (permalink / raw)
  To: Lin Feng; +Cc: axboe, linux-kernel, linux-bcache

On 7/20/21 6:32 PM, Lin Feng wrote:
> Original codes:
> BITMASK(CACHE_SYNC,			struct cache_sb, flags, 0, 1);
> BITMASK(CACHE_DISCARD,			struct cache_sb, flags, 1, 1);
> BITMASK(CACHE_REPLACEMENT,		struct cache_sb, flags, 2, 3);
> ...
> BITMASK(BDEV_CACHE_MODE,		struct cache_sb, flags, 0, 4);
>
> Should BDEV_CACHE_MODE bits start from bit-nr 5(2+3) else it overlaps
> with previous defined bit chunks, since we have 4 types of cache modes,
> BDEV_CACHE_MODE will overwrite CACHE_SYNC and CACHE_DISCARD bits.

The overlap won't happen, previous lines are for cache device, and what 
you modified is for backing device.

And your patch changes the on-disk format, which is unacceptable anyway.


Coly Li

>
> This bug stays there since first upstream version of bcache, don't know
> why it lives so long, or am i missing something, please point me out
> if I'm wrong, thanks!
>
> Signed-off-by: Lin Feng <linf@wangsu.com>
> ---
>   include/uapi/linux/bcache.h | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/uapi/linux/bcache.h b/include/uapi/linux/bcache.h
> index cf7399f03b71..dccd89756451 100644
> --- a/include/uapi/linux/bcache.h
> +++ b/include/uapi/linux/bcache.h
> @@ -288,7 +288,7 @@ BITMASK(CACHE_REPLACEMENT,		struct cache_sb, flags, 2, 3);
>   #define CACHE_REPLACEMENT_FIFO		1U
>   #define CACHE_REPLACEMENT_RANDOM	2U
>   
> -BITMASK(BDEV_CACHE_MODE,		struct cache_sb, flags, 0, 4);
> +BITMASK(BDEV_CACHE_MODE,		struct cache_sb, flags, 5, 4);
>   #define CACHE_MODE_WRITETHROUGH		0U
>   #define CACHE_MODE_WRITEBACK		1U
>   #define CACHE_MODE_WRITEAROUND		2U



^ permalink raw reply	[flat|nested] 3+ messages in thread

* Re: [PATCH] bcache: fix wrong BITMASK offset value for BDEV_CACHE_MODE
  2022-05-13 15:20 ` Coly Li
@ 2022-05-16  1:50   ` Lin Feng
  0 siblings, 0 replies; 3+ messages in thread
From: Lin Feng @ 2022-05-16  1:50 UTC (permalink / raw)
  To: Coly Li; +Cc: axboe, linux-kernel, linux-bcache



On 5/13/22 23:20, Coly Li wrote:
> On 7/20/21 6:32 PM, Lin Feng wrote:
>> Original codes:
>> BITMASK(CACHE_SYNC,			struct cache_sb, flags, 0, 1);
>> BITMASK(CACHE_DISCARD,			struct cache_sb, flags, 1, 1);
>> BITMASK(CACHE_REPLACEMENT,		struct cache_sb, flags, 2, 3);
>> ...
>> BITMASK(BDEV_CACHE_MODE,		struct cache_sb, flags, 0, 4);
>>
>> Should BDEV_CACHE_MODE bits start from bit-nr 5(2+3) else it overlaps
>> with previous defined bit chunks, since we have 4 types of cache modes,
>> BDEV_CACHE_MODE will overwrite CACHE_SYNC and CACHE_DISCARD bits.
> 
> The overlap won't happen, previous lines are for cache device, and what
> you modified is for backing device.
> 
> And your patch changes the on-disk format, which is unacceptable anyway.
> 

Yes, you are right, this patch happened as I started reading bcache codes,
I did not get a whole picture of bcache at that time, I'm sorry for making
noise.

Thank you, Coly!

linfeng
> 
> Coly Li
> 
>>
>> This bug stays there since first upstream version of bcache, don't know
>> why it lives so long, or am i missing something, please point me out
>> if I'm wrong, thanks!
>>
>> Signed-off-by: Lin Feng <linf@wangsu.com>
>> ---
>>    include/uapi/linux/bcache.h | 2 +-
>>    1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/include/uapi/linux/bcache.h b/include/uapi/linux/bcache.h
>> index cf7399f03b71..dccd89756451 100644
>> --- a/include/uapi/linux/bcache.h
>> +++ b/include/uapi/linux/bcache.h
>> @@ -288,7 +288,7 @@ BITMASK(CACHE_REPLACEMENT,		struct cache_sb, flags, 2, 3);
>>    #define CACHE_REPLACEMENT_FIFO		1U
>>    #define CACHE_REPLACEMENT_RANDOM	2U
>>    
>> -BITMASK(BDEV_CACHE_MODE,		struct cache_sb, flags, 0, 4);
>> +BITMASK(BDEV_CACHE_MODE,		struct cache_sb, flags, 5, 4);
>>    #define CACHE_MODE_WRITETHROUGH		0U
>>    #define CACHE_MODE_WRITEBACK		1U
>>    #define CACHE_MODE_WRITEAROUND		2U
> 


^ permalink raw reply	[flat|nested] 3+ messages in thread

end of thread, other threads:[~2022-05-16  1:50 UTC | newest]

Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed)
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2021-07-20 10:32 [PATCH] bcache: fix wrong BITMASK offset value for BDEV_CACHE_MODE Lin Feng
2022-05-13 15:20 ` Coly Li
2022-05-16  1:50   ` Lin Feng

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