Message-ID: <9ac23fbe-7bfe-68f6-a9b5-6c722d0fe629@linux.alibaba.com>
Date:   Thu, 9 Feb 2023 13:01:11 +0800
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Subject: Re: [PATCH 4/4] erofs: simplify the name collision checking in share
 domain mode
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From:   Jingbo Xu <jefflexu@linux.alibaba.com>
To:     xiang@kernel.org, chao@kernel.org, linux-erofs@lists.ozlabs.org,
        zhujia.zj@bytedance.com, houtao1@huawei.com
Cc:     huyue2@coolpad.com, linux-kernel@vger.kernel.org
References: <cover.1675840368.git.jefflexu@linux.alibaba.com>
 <489d47915bcc71ef3c3ec7b8a437ec6e09c4c3db.1675840368.git.jefflexu@linux.alibaba.com>
In-Reply-To: <489d47915bcc71ef3c3ec7b8a437ec6e09c4c3db.1675840368.git.jefflexu@linux.alibaba.com>
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On 2/8/23 3:17 PM, Jingbo Xu wrote:
> When share domain is enabled, data blobs can be shared among filesystem
> instances in the same domain for data deduplication, while bootstrap
> blobs are always dedicated to the corresponding filesystem instance, and
> have no need to be shared.
> 
> In the initial implementation of share domain (commit 7d41963759fe
> ("erofs: Support sharing cookies in the same domain")), bootstrap blobs
> are also in the share domain, and thus can be referenced by the
> following filesystem instances.  In this case, mounting twice with the
> same fsid and domain_id will trigger warning in sysfs.  Commit
> 27f2a2dcc626 ("erofs: check the uniqueness of fsid in shared domain in
> advance") fixes this by introducing the name collision checking.
> 
> This patch attempts to fix the above issue in another simpler way.
> Since the bootstrap blobs have no need to be shared, move them out of
> the share domain, so that one bootstrap blob can not be referenced by
> other filesystem instances.  Attempt to mount twice with the same fsid
> and domain_id will fail with info of duplicate cookies, which is
> consistent with the behavior in non-share-domain mode.
> 

In non-share-domain mode, the uniqueness of primary data blob is
actually guaranteed by fscache_acquire_volume(), since
fscache_acquire_volume() will fail if attempt to mount the same fsid twice.

Thus hold on for this patch.


-- 
Thanks,
Jingbo