Changes since V3: 1. Avoid race condition. 1.1. Relinquish the volume before removing the domain from list. 1.2. Hold erofs_domain_list_lock before dec the refcnt of domain. 2. Relinquish previously registered erofs_fscache in erofs_fscache_domain_init_cookie()'s error handling path. 3. Some code cleanups without logic change. [Kernel Patchset] =============== Git tree: https://github.com/userzj/linux.git zhujia/shared-domain-v4 Git web: https://github.com/userzj/linux/tree/zhujia/shared-domain-v4 [User Daemon for Quick 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 [E2E Container Demo for Quick Test] =================================== [Issue] https://github.com/containerd/nydus-snapshotter/issues/161 [PR] https://github.com/containerd/nydus-snapshotter/pull/162 [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. RFC: https://lore.kernel.org/all/YxAlO%2FDHDrIAafR2@B-P7TQMD6M-0146.local/ V1: https://lore.kernel.org/all/20220902034748.60868-1-zhujia.zj@xxxxxxxxxxxxx/ V2: https://lore.kernel.org/all/20220902105305.79687-1-zhujia.zj@xxxxxxxxxxxxx/ V3: https://lore.kernel.org/all/20220914105041.42970-1-zhujia.zj@xxxxxxxxxxxxx/ Jia Zhu (6): erofs: use kill_anon_super() to kill super in fscache mode erofs: code clean up for fscache erofs: introduce fscache-based domain erofs: introduce a pseudo mnt to manage shared cookies erofs: Support sharing cookies in the same domain erofs: introduce 'domain_id' mount option fs/erofs/fscache.c | 253 ++++++++++++++++++++++++++++++++++++++------ fs/erofs/internal.h | 30 ++++-- fs/erofs/super.c | 72 ++++++++++--- fs/erofs/sysfs.c | 19 +++- 4 files changed, 317 insertions(+), 57 deletions(-) -- 2.20.1
