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Diffstat (limited to 'Documentation/filesystems/aufs/design/06xattr.txt')
| -rw-r--r-- | Documentation/filesystems/aufs/design/06xattr.txt | 96 |
1 files changed, 0 insertions, 96 deletions
diff --git a/Documentation/filesystems/aufs/design/06xattr.txt b/Documentation/filesystems/aufs/design/06xattr.txt deleted file mode 100644 index 8aad929b8..000000000 --- a/Documentation/filesystems/aufs/design/06xattr.txt +++ /dev/null @@ -1,96 +0,0 @@ - -# Copyright (C) 2014-2015 Junjiro R. Okajima -# -# This program is free software; you can redistribute it and/or modify -# it under the terms of the GNU General Public License as published by -# the Free Software Foundation; either version 2 of the License, or -# (at your option) any later version. -# -# This program is distributed in the hope that it will be useful, -# but WITHOUT ANY WARRANTY; without even the implied warranty of -# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the -# GNU General Public License for more details. -# -# You should have received a copy of the GNU General Public License -# along with this program; if not, write to the Free Software -# Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA - - -Listing XATTR/EA and getting the value ----------------------------------------------------------------------- -For the inode standard attributes (owner, group, timestamps, etc.), aufs -shows the values from the topmost existing file. This behaviour is good -for the non-dir entries since the bahaviour exactly matches the shown -information. But for the directories, aufs considers all the same named -entries on the lower branches. Which means, if one of the lower entry -rejects readdir call, then aufs returns an error even if the topmost -entry allows it. This behaviour is necessary to respect the branch fs's -security, but can make users confused since the user-visible standard -attributes don't match the behaviour. -To address this issue, aufs has a mount option called dirperm1 which -checks the permission for the topmost entry only, and ignores the lower -entry's permission. - -A similar issue can happen around XATTR. -getxattr(2) and listxattr(2) families behave as if dirperm1 option is -always set. Otherwise these very unpleasant situation would happen. -- listxattr(2) may return the duplicated entries. -- users may not be able to remove or reset the XATTR forever, - - -XATTR/EA support in the internal (copy,move)-(up,down) ----------------------------------------------------------------------- -Generally the extended attributes of inode are categorized as these. -- "security" for LSM and capability. -- "system" for posix ACL, 'acl' mount option is required for the branch - fs generally. -- "trusted" for userspace, CAP_SYS_ADMIN is required. -- "user" for userspace, 'user_xattr' mount option is required for the - branch fs generally. - -Moreover there are some other categories. Aufs handles these rather -unpopular categories as the ordinary ones, ie. there is no special -condition nor exception. - -In copy-up, the support for XATTR on the dst branch may differ from the -src branch. In this case, the copy-up operation will get an error and -the original user operation which triggered the copy-up will fail. It -can happen that even all copy-up will fail. -When both of src and dst branches support XATTR and if an error occurs -during copying XATTR, then the copy-up should fail obviously. That is a -good reason and aufs should return an error to userspace. But when only -the src branch support that XATTR, aufs should not return an error. -For example, the src branch supports ACL but the dst branch doesn't -because the dst branch may natively un-support it or temporary -un-support it due to "noacl" mount option. Of course, the dst branch fs -may NOT return an error even if the XATTR is not supported. It is -totally up to the branch fs. - -Anyway when the aufs internal copy-up gets an error from the dst branch -fs, then aufs tries removing the just copied entry and returns the error -to the userspace. The worst case of this situation will be all copy-up -will fail. - -For the copy-up operation, there two basic approaches. -- copy the specified XATTR only (by category above), and return the - error unconditionally if it happens. -- copy all XATTR, and ignore the error on the specified category only. - -In order to support XATTR and to implement the correct behaviour, aufs -chooses the latter approach and introduces some new branch attributes, -"icexsec", "icexsys", "icextr", "icexusr", and "icexoth". -They correspond to the XATTR namespaces (see above). Additionally, to be -convenient, "icex" is also provided which means all "icex*" attributes -are set (here the word "icex" stands for "ignore copy-error on XATTR"). - -The meaning of these attributes is to ignore the error from setting -XATTR on that branch. -Note that aufs tries copying all XATTR unconditionally, and ignores the -error from the dst branch according to the specified attributes. - -Some XATTR may have its default value. The default value may come from -the parent dir or the environment. If the default value is set at the -file creating-time, it will be overwritten by copy-up. -Some contradiction may happen I am afraid. -Do we need another attribute to stop copying XATTR? I am unsure. For -now, aufs implements the branch attributes to ignore the error. |