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@xxxxxxxxxxxxx/ 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(-) -- 2.20.1
