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acl.h | ||
dinode.h | ||
dir.h | ||
dirhash.h | ||
extattr.h | ||
gjournal.h | ||
inode.h | ||
quota.h | ||
README.acls | ||
README.extattr | ||
ufs_acl.c | ||
ufs_bmap.c | ||
ufs_dirhash.c | ||
ufs_extattr.c | ||
ufs_extern.h | ||
ufs_gjournal.c | ||
ufs_inode.c | ||
ufs_lookup.c | ||
ufs_quota.c | ||
ufs_vfsops.c | ||
ufs_vnops.c | ||
ufsmount.h |
UFS Extended Attributes Copyright The UFS Extended Attributes implementation is copyright Robert Watson, and is made available under a Berkeley-style license. About UFS Extended Attributes Extended attributes allow the association of additional arbitrary meta-data with files and directories. Extended attributes are defined in the form name=value, where name is an nul-terminated string in the style of a filename, and value is a binary blob of zero or more bytes. The UFS extended attribute service layers support for extended attributes onto a backing file, in the style of the quota implementation, meaning that it requires no underlying format changes in the filesystem. This design choice exchanges simplicity, usability and easy deployment for performance. When defined, extended attribute names exist in a series of disjoint namespaces: currently, two namespaces are defined: EXTATTR_NAMESPACE_SYSTEM and EXTATTR_NAMESPACE_USER. The primary distinction lies in the protection model: USER EAs are protected using the normal inode protections, whereas SYSTEM EAs require privilege to access or modify. Using UFS Extended Attributes Support for UFS extended attributes is natively available in UFS2, and requires no special configuration. For reliability, administrative, and performance reasons, if you plan to use extended attributes, it is recommended that you use UFS2 in preference to UFS1. Support for UFS extended attributes may be enabled for UFS1 by adding: options UFS_EXTATTR to your kernel configuration file. This allows UFS-based filesystems to support extended attributes, but requires manual administration of EAs using the extattrctl tool, including the starting of EA support for each filesystem, and the enabling of individual attributes for the file system. The extattrctl utility may be used to initialize backing files before first use, to start and stop EA service on a filesystem, and to enable and disable named attributes. The command lines for extattrctl take the following forms: extattrctl start [path] extattrctl stop [path] extattrctl initattr [-f] [-p path] [attrsize] [attrfile] extattrctl enable [path] [attrnamespace] [attrname] [attrfile] extattrctl disable [path] [attrnamespace] [attrname] In each case, [path] is used to indicate the mounted filesystem on which to perform the operation. [attrnamespace] refers to the namespace in which the attribute is being manipulated, and may be "system" or "user". The [attrname] is the attribute name to use for the operation. The [attrfile] argument specifies the attribute backing file to use. When using the "initattr" function to initialize a backing file, the maximum size of attribute data must be defined in bytes using the [attrsize] field. Optionally, the [-p path] argument may be used to indicate to extattrctl that it should pre-allocate space for EA data, rather than creating a sparse backing file. This prevents attribute operations from failing in low disk-space conditions (which can be important when EAs are used for security purposes), but pre-allocation will consume space proportional to the product of the defined maximum attribute size and number of attributes on the specified filesystem. Manual configuration increases administrative overhead, but also introduces the possibility of race conditions during filesystem mount, if EAs are used to support other features, as starting the EAs manually is not atomic with the mount operation. To address this problem, an additional kernel option may be defined to auto-start EAs on a UFS file system based on special directories at mount-time: options UFS_EXTATTR_AUTOSTART If this option is defined, UFS will search for a ".attribute" sub-directory of the filesystem root during the mount operation. If it is found, EA support will be started for the filesystem. UFS will then search for "system" and "user" sub-directories of the ".attribute" directory for any potential backing files, and enable an EA for each valid backing file with the name of the backing file as the attribute name. For example, by creating the following tree, the two EAs, posix1e.acl_access and posix1e.acl_default will be enabled in the system namespace of the root filesystem, reserving space for attribute data: mkdir -p /.attribute/system cd /.attribute/system extattrctl initattr -p / 388 posix1e.acl_access extattrctl initattr -p / 388 posix1e.acl_default On the next mount of the root filesystem, the attributes will be automatically started.