linux-kernel - Re: [PATCH 4/4] erofs: simplify the name collision checking in share domain mode

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Date:   Thu, 9 Feb 2023 13:01:11 +0800
From:   Jingbo Xu <jefflexu@...ux.alibaba.com>
To:     xiang@...nel.org, chao@...nel.org, linux-erofs@...ts.ozlabs.org,
        zhujia.zj@...edance.com, houtao1@...wei.com
Cc:     huyue2@...lpad.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/4] erofs: simplify the name collision checking in share
 domain mode



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