1 files changed, 110 insertions, 0 deletions
diff --git a/man/man5/attr.5 b/man/man5/attr.5
new file mode 100644
index 0000000..4d82071
--- /dev/null
+++ b/man/man5/attr.5
@@ -0,0 +1,110 @@
+.\"
+.\" Extended attributes manual page
+.\"
+.\" (C) Andreas Gruenbacher, 2000
+.\" (C) Silicon Graphics Inc, 2001
+.\"
+.TH ATTR 5
+.SH NAME
+Extended attributes
+.SH DESCRIPTION
+Extended attributes are name:value pairs associated permanently with
+files and directories, similar to the environment strings associated
+with a process.
+An attribute may be defined or undefined.
+If it is defined, its value may be empty or non-empty.
+.PP
+Extended attributes are extensions to the normal attributes which are
+associated with all inodes in the system (i.e. the
+.BR stat (2)
+data).
+They are often used to provide additional functionality
+to a filesystem \- for example, additional security features such as
+Access Control Lists (ACLs) may be implemented using extended attributes.
+.PP
+Users with search access to a file or directory may retrieve a list of
+attribute names defined for that file or directory.
+.PP
+Extended attributes are accessed as atomic objects.
+Reading retrieves the whole value of an attribute and stores it in a buffer.
+Writing replaces any previous value with the new value.
+.PP
+Currently, support for extended attributes is implemented on Linux by
+the ext2, ext3 and XFS filesystem patches, which can be downloaded from
+.B http://acl.bestbits.at/
+and
+.B http://oss.sgi.com/projects/xfs/
+respectively.
+.SH EXTENDED ATTRIBUTE NAMESPACES
+Attribute names are zero-terminated strings and typically have a short
+(filesystem dependent) length.
+The attribute name is always specified in the full
+.IR namespace.attribute
+form, eg.
+.I user.mime_type
+or
+.IR system.posix_acl_access .
+.PP
+The namespace mechanism is used to define different classes of extended
+attributes.
+These different classes exist for several reasons, e.g. the permissions
+and capabilities required for manipulating extended attributes of one
+namespace may differ to another.
+They have also been used to distinguish filesystem-specific attribute
+names from canonical, filesystem-independent attribute names.
+.PP
+The extended attribute namespace is always specified as the first
+component of the name.
+This greatly simplifies certain operations, and provides a consistent,
+explicit interface for all operations.
+.PP
+Extended
+.I user
+attributes may be assigned to files and directories for storing arbitrary
+additional information such as the mime type, character set or encoding
+of a file.
+User attributes are subject to the same permissions as the contents of a file.
+The file owner can decide who is allowed to read and/or set these attributes.
+.PP
+Extended
+.I system
+attributes are used by the kernel to store system objects such as
+Access Control Lists and Capabilities. 
+Read and write access permissions to system attributes
+depend on the policy implemented for each system attribute implemented
+in the kernel.
+.PP
+Additional types of extended attributes with different access permissions,
+such as attributes that are accessible only to processes trusted by the
+kernel, may be added in the future.
+.SH FILESYSTEM DIFFERENCES
+The kernel and the filesystem may place limits on the maximum number
+and size of extended attributes that can be associated with a file.
+.PP
+In the current ext2 and ext3 filesystem implementations, all extended
+attributes must fit on a single filesystem block (1024, 2048 or 4096 bytes,
+depending on the block size specified when the filesystem
+was created). This limit may be removed in a future version.
+Device special files cannot be associated with extended user attributes
+(but they may be associated with extended system attributes). Permissions
+of device special files define access to the devices rather than to the
+device special files.
+.PP
+In the XFS filesystem implementation, there is no practical limit on the
+number of extended attributes associated with a file, and the algorithms
+used to store extended attribute information on disk are scalable (stored
+either inline in the inode, as an extent, or in a B+ tree).
+XFS allows extended attributes to be associated with device inodes.
+.SH ADDITIONAL NOTES
+Since the filesystems on which extended attributes are stored might also
+be used on architectures with a different byte order and machine word
+size, care should be taken to store attribute values in an architecture
+independent format.
+.SH AUTHORS
+Andreas Gruenbacher,
+.RI < a.gruenbacher@computer.org >
+and the SGI XFS development team,
+.RI < linux-xfs@oss.sgi.com >.
+.SH SEE ALSO
+getfattr(1),
+setfattr(1).