From mboxrd@z Thu Jan 1 00:00:00 1970 From: Chao Yu Subject: Re: [PATCH 2/2] f2fs: support {d,id,did,x}node checksum Date: Thu, 1 Feb 2018 22:20:42 +0800 Message-ID: <55f144df-4419-3642-5b35-c8885cdb7354@kernel.org> References: <20180127094301.29154-1-yuchao0@huawei.com> <20180127094301.29154-2-yuchao0@huawei.com> <20180131020213.GA86468@jaegeuk-macbookpro.roam.corp.google.com> <20180131221531.GC12901@jaegeuk-macbookpro.roam.corp.google.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20180131221531.GC12901@jaegeuk-macbookpro.roam.corp.google.com> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: Jaegeuk Kim , Chao Yu Cc: linux-f2fs-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org List-Id: linux-f2fs-devel.lists.sourceforge.net On 2018/2/1 6:15, Jaegeuk Kim wrote: > On 01/31, Chao Yu wrote: >> On 2018/1/31 10:02, Jaegeuk Kim wrote: >>> What if we want to add more entries in addition to node_checksum? Do we have >>> to add a new feature flag at every time? How about adding a layout value instead >> >> Hmm.. for previous implementation, IMO, we'd better add a new feature flag at >> every time, otherwise, w/ extra_nsize only, in current image, we can know a >> valid range of extended area in node block, but we don't know which >> fields/features are valid/enabled or not. >> >> One more thing is that if we can add one feature flag for each field, we got one >> more chance to disable it dynamically. >> >>> of extra_nsize? For example, layout #1 means node_checksum with extra_nsize=X? >>> >>> >>> What does 1017 mean? We need to make this structure more flexibly for new >> >> Yes, using raw 1017 is not appropriate here. >> >>> entries. Like this? >>> union { >>> struct node_v1; >>> struct node_v2; >>> struct node_v3; >>> ... >>> struct direct_node dn; >>> struct indirect_node in; >>> }; >>> }; >>> >>> struct node_v1 { >>> __le32 data[DEF_ADDRS_PER_BLOCK - V1_NSIZE=1]; >>> __le32 node_checksum; >>> } >>> >>> struct node_v2 { >>> __le32 data[DEF_ADDRS_PER_BLOCK - V2_NSIZE=500]; >> >> Hmm.. If we only need to add one more 4 bytes field in struct node_v2, but >> V2_NSIZE is defined as fixed 500, there must be 492 bytes wasted. >> >> Or we can define V2_NSIZE as 8, but if there comes more and more extended >> fields, node version count can be a large number, it results in complicated >> version recognization and handling. >> >> One more question is how can we control which fields are valid or not in >> comp[Vx_NSIZE]? >> >> >> Anyway, what I'm thinking is maybe we can restructure layout of node block like >> the one used by f2fs_inode: >> >> struct f2fs_node { >> union { >> struct f2fs_inode i; >> union { >> struct { >> __le32 node_checksum; >> __le32 feature_field_1; >> __le32 feature_field_2; >> .... >> __le32 addr[]; >> >> }; >> struct direct_node dn; >> struct indirect_node in; >> }; >> }; >> struct node_footer footer; >> } __packed; >> >> Moving all extended fields to the head of f2fs_node, so we don't have to use >> macro to indicate actual size of addr. > > Thinking what'd be the best way. My concern is, once getting more entries, we OK, I think we need more discussion.. ;) > can't set each of features individually. Like the second entry should have Oh, that will be hard. If we have to avoid that, we have to tag in somewhere e.g. f2fs_inode::i_flags2 to indicate which new field in f2fs_node is valid, for example: #define F2FS_NODE_CHECKSUM 0x0001 #define F2FS_NODE_FIELD1 0x0002 #define F2FS_NODE_FIELD2 0x0004 union { struct { __le32 node_checksum; __le32 field_1; __le32 field_2; .... __le32 addr[]; }; struct direct_node dn; struct indirect_node in; }; f2fs_inode::i_flags2 = F2FS_NODE_CHECKSUM | F2FS_NODE_FIELD1 indicates that f2fs_node::node_checksum and f2fs_node::field_1 are valid; f2fs_inode::i_flags2 = F2FS_NODE_FIELD1 | F2FS_NODE_FIELD2 indicates that f2fs_node::field_1 and f2fs_node::field_2 are valid. Any thoughts? Thanks, > enabled node_checksum, which we may not want to do. > >> >> Thanks, >> >>> __le32 comp[V2_NSIZE]; >>> } >>> ... >>> >>>> + }; >>>> + struct direct_node dn; >>>> + struct indirect_node in; >>>> + }; >>>> }; >>>> struct node_footer footer; >>>> } __packed; >>>> -- >>>> 2.15.0.55.gc2ece9dc4de6 >>> >>> . >>>