Re: [PATCH] bcache: fix wrong BITMASK offset value for BDEV_CACHE_MODE

[Lin Feng]

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@xxxxxxxxxx>
> > ---
> >    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