[PATCH V2 0/5] Introduce erofs shared domain

[Jia Zhu]

[E2E Container Demo for Quick Test]
===================================
[Issue]
     https://github.com/containerd/nydus-snapshotter/issues/161

[Pull Request]
     https://github.com/containerd/nydus-snapshotter/pull/162

在 2022/9/2 18:53, Jia Zhu 写道:
> Changes since V1:
> 0. Only initialize one pseudo fs to manage anonymous inodes(cookies).
> 1. Remove ctx's 'ref' field and replace it with inode's i_count.
> 2. Add lock in erofs_fscache_unregister_cookie() to avoid race condition
>     between cookie's get/put/search.
> 3. Remove useless blank lines.
> 
> [Kernel Patchset]
> ===============
> Git tree:
> 	https://github.com/userzj/linux.git zhujia/shared-domain-v2
> Git web:
> 	https://github.com/userzj/linux/tree/zhujia/shared-domain-v2
> 
> [Background]
> ============
> In ondemand read mode, we use individual volume to present an erofs
> mountpoint, cookies to present bootstrap and data blobs.
> 
> In which case, since cookies can't be shared between fscache volumes,
> even if the data blobs between different mountpoints are exactly same,
> they can't be shared.
> 
> [Introduction]
> ==============
> Here we introduce erofs shared domain to resolve above mentioned case.
> Several erofs filesystems can belong to one domain, and data blobs can
> be shared among these erofs filesystems of same domain.
> 
> [Usage]
> Users could specify 'domain_id' mount option to create or join into a
> domain which reuses the same cookies(blobs).
> 
> [Design]
> ========
> 1. Use pseudo mnt to manage domain's lifecycle.
> 2. Use a linked list to maintain & traverse domains.
> 3. Use pseudo sb to create anonymous inode for recording cookie's info
>     and manage cookies lifecycle.
> 
> [Flow Path]
> ===========
> 1. User specify a new 'domain_id' in mount option.
>     1.1 Traverse domain list, compare domain_id with existing domain.[Miss]
>     1.2 Create a new domain(volume), add it to domain list.
>     1.3 Traverse pseudo sb's inode list, compare cookie name with
>         existing cookies.[Miss]
>     1.4 Alloc new anonymous inodes and cookies.
> 
> 2. User specify an existing 'domain_id' in mount option and the data
>     blob is existed in domain.
>     2.1 Traverse domain list, compare domain_id with existing domain.[Hit]
>     2.2 Reuse the domain and increase its refcnt.
>     2.3 Traverse pseudo sb's inode list, compare cookie name with
>     	   existing cookies.[Hit]
>     2.4 Reuse the cookie and increase its refcnt.
> [Test]
> ======
> Git web:
> 	https://github.com/userzj/demand-read-cachefilesd/tree/shared-domain
> More test cases will be added to:
> 	https://git.kernel.org/pub/scm/linux/kernel/git/xiang/erofs-utils.git/log/?h=experimental-tests-fscache
> 
> RFC: https://lore.kernel.org/all/YxAlO%2FDHDrIAafR2@B-P7TQMD6M-0146.local/
> V1: https://lore.kernel.org/all/20220902034748.60868-1-zhujia.zj@bytedance.com/
> 
> 
> Jia Zhu (5):
>    erofs: add 'domain_id' mount option for on-demand read sementics
>    erofs: introduce fscache-based domain
>    erofs: add 'domain_id' prefix when register sysfs
>    erofs: remove duplicated unregister_cookie
>    erofs: support fscache based shared domain
> 
>   fs/erofs/fscache.c  | 168 +++++++++++++++++++++++++++++++++++++++++++-
>   fs/erofs/internal.h |  31 +++++++-
>   fs/erofs/super.c    |  94 +++++++++++++++++++------
>   fs/erofs/sysfs.c    |  11 ++-
>   4 files changed, 278 insertions(+), 26 deletions(-)
>