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Subject: Re: [PATCH] ceph: use correct index when encoding client supported
 features
To:     =?UTF-8?Q?Lu=c3=ads_Henriques?= <lhenriques@suse.de>,
        Jeff Layton <jlayton@kernel.org>,
        Ilya Dryomov <idryomov@gmail.com>
Cc:     ceph-devel@vger.kernel.org, linux-kernel@vger.kernel.org
References: <20220524160627.20893-1-lhenriques@suse.de>
From:   Xiubo Li <xiubli@redhat.com>
Message-ID: <d1f22b3b-7415-0fdb-e702-24f2a7b0b939@redhat.com>
Date:   Thu, 26 May 2022 08:55:15 +0800
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On 5/25/22 12:06 AM, Luís Henriques wrote:
> Feature bits have to be encoded into the correct locations.  This hasn't
> been an issue so far because the only hole in the feature bits was in bit
> 10 (CEPHFS_FEATURE_RECLAIM_CLIENT), which is located in the 2nd byte.  When
> adding more bits that go beyond the this 2nd byte, the bug will show up.
>
> Fixes: 9ba1e224538a ("ceph: allocate the correct amount of extra bytes for the session features")
> Signed-off-by: Luís Henriques <lhenriques@suse.de>
> ---
>   fs/ceph/mds_client.c | 7 +++++--
>   fs/ceph/mds_client.h | 2 --
>   2 files changed, 5 insertions(+), 4 deletions(-)
>
> I hope I got this code right.  I found this issue when trying to add an
> extra feature bit that would go beyond bit 15 and that wasn't showing up
> on the MDS side.
>
> diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c
> index 1bd3e1bb0fdf..77e742b6fd30 100644
> --- a/fs/ceph/mds_client.c
> +++ b/fs/ceph/mds_client.c
> @@ -1220,14 +1220,17 @@ static int encode_supported_features(void **p, void *end)
>   	if (count > 0) {
>   		size_t i;
>   		size_t size = FEATURE_BYTES(count);
> +		unsigned long bit;
>   
>   		if (WARN_ON_ONCE(*p + 4 + size > end))
>   			return -ERANGE;
>   
>   		ceph_encode_32(p, size);
>   		memset(*p, 0, size);
> -		for (i = 0; i < count; i++)
> -			((unsigned char*)(*p))[i / 8] |= BIT(feature_bits[i] % 8);
> +		for (i = 0; i < count; i++) {
> +			bit = feature_bits[i];
> +			((unsigned char *)(*p))[bit / 8] |= BIT(bit % 8);
> +		}
>   		*p += size;
>   	} else {
>   		if (WARN_ON_ONCE(*p + 4 > end))
> diff --git a/fs/ceph/mds_client.h b/fs/ceph/mds_client.h
> index 33497846e47e..12901e3a6823 100644
> --- a/fs/ceph/mds_client.h
> +++ b/fs/ceph/mds_client.h
> @@ -45,8 +45,6 @@ enum ceph_feature_type {
>   	CEPHFS_FEATURE_MULTI_RECONNECT,		\
>   	CEPHFS_FEATURE_DELEG_INO,		\
>   	CEPHFS_FEATURE_METRIC_COLLECT,		\
> -						\
> -	CEPHFS_FEATURE_MAX,			\
>   }
>   #define CEPHFS_FEATURES_CLIENT_REQUIRED {}
>   

LGTM. Just one small fix in the comment, since you have removed the 
'CEPHFS_FEATURE_MAX', which makes no sense any more:


diff --git a/fs/ceph/mds_client.h b/fs/ceph/mds_client.h
index 33497846e47e..ac49344ea79e 100644
--- a/fs/ceph/mds_client.h
+++ b/fs/ceph/mds_client.h
@@ -33,10 +33,6 @@ enum ceph_feature_type {
         CEPHFS_FEATURE_MAX = CEPHFS_FEATURE_METRIC_COLLECT,
  };

-/*
- * This will always have the highest feature bit value
- * as the last element of the array.
- */
  #define CEPHFS_FEATURES_CLIENT_SUPPORTED {     \
         0, 1, 2, 3, 4, 5, 6, 7,                 \
         CEPHFS_FEATURE_MIMIC,                   \

Merged into the testing branch.

Thanks Luis.

-- Xiubo