240 lines
5.1 KiB
Groff
240 lines
5.1 KiB
Groff
'\"macro stdmacro
|
|
.if n .pH g2.attr_get @(#)attr_get 1.1 of 6/12/95
|
|
.TH ATTR_GET 2
|
|
.SH NAME
|
|
attr_get, attr_getf \- get the value of a user attribute of a filesystem object
|
|
.Op c p a
|
|
.SH C SYNOPSIS
|
|
.PP
|
|
.sp
|
|
.nf
|
|
.B #include <sys/attributes.h>
|
|
.sp
|
|
.B "int attr_get (const char \(**path, const char \(**attrname, "
|
|
.B " char \(**attrvalue, int \(**valuelength, int flags);"
|
|
.PP
|
|
.B "int attr_getf (int fd, const char \(**attrname, "
|
|
.B " char \(**attrvalue, int \(**valuelength, int flags);"
|
|
.Op
|
|
.SH OVERVIEW
|
|
The
|
|
.I attr
|
|
group of system calls implement the ability for a user to attach
|
|
name/value pairs to objects within the filesystem.
|
|
.P
|
|
They could be used to store meta-information about the file.
|
|
For example "character-set=kanji" could tell a document browser to
|
|
use the Kanji character set when displaying that document
|
|
and "thumbnail=..." could provide a reduced resolution overview of a
|
|
high resolution graphic image.
|
|
.P
|
|
The
|
|
.I names
|
|
can be up to MAXNAMELEN bytes in length, terminated by the first 0 byte.
|
|
The intent is that they be printable ASCII (or other character set)
|
|
names for the attribute.
|
|
.P
|
|
The
|
|
.I values
|
|
can be up to ATTR_MAX_VALUELEN (currently 64KB) of arbitrary binary data.
|
|
.P
|
|
Attributes can be attached to all types of inodes:
|
|
regular files, directories, symbolic links, device nodes, etc.
|
|
.P
|
|
There are 2 disjoint attribute name spaces associated with every
|
|
filesystem object.
|
|
They are the
|
|
.B root
|
|
and
|
|
.B user
|
|
address spaces.
|
|
The
|
|
.B root
|
|
address space is accessable only to the super-user,
|
|
and then only by specifying a flag argument to the function call.
|
|
Other users will not see or be able to modify attributes in the
|
|
.B root
|
|
address space.
|
|
The
|
|
.B user
|
|
address space is protected by the normal file permissions mechanism,
|
|
so the owner of the file can decide who is able to see and/or modify
|
|
the value of attributes on any particular file.
|
|
.P
|
|
Attributes are currently supported only in the XFS filesystem type.
|
|
.SH DESCRIPTION
|
|
The
|
|
.I attr_get
|
|
and
|
|
.I attr_getf
|
|
functions provide a way to retrieve the value of an attribute.
|
|
.P
|
|
.I Path\^
|
|
points to a path name for a filesystem object, and
|
|
.I fd\^
|
|
refers to the file descriptor associated with a file.
|
|
If the attribute
|
|
.I attrname
|
|
exists, the value associated with it will be copied into the
|
|
.I attrvalue
|
|
buffer.
|
|
The
|
|
.I valuelength
|
|
argument is an input/output argument that on the call to
|
|
.I attr_get
|
|
should contain the maximum size of attribute value the
|
|
process is willing to accept.
|
|
On return, the
|
|
.I valuelength
|
|
will have been modified to show the actual size of the
|
|
attribute value returned.
|
|
The
|
|
.I flags
|
|
argument can contain the following symbols bitwise OR\'ed together:
|
|
.TP
|
|
.SM
|
|
\%ATTR_ROOT
|
|
Look for
|
|
.I attrname
|
|
in the
|
|
.B root
|
|
address space, not in the
|
|
.B user
|
|
address space.
|
|
(limited to use by super-user only)
|
|
.TP
|
|
.SM
|
|
\%ATTR_DONTFOLLOW
|
|
Do not follow symbolic links when resolving a
|
|
.I path
|
|
on an
|
|
.I attr_get
|
|
function call.
|
|
The default is to follow symbolic links.
|
|
.PP
|
|
.I attr_get
|
|
will fail if one or more of the following are true:
|
|
.TP 17
|
|
.SM
|
|
\%[ENOATTR]
|
|
The attribute name given is not associated with the indicated
|
|
filesystem object.
|
|
.TP
|
|
.SM
|
|
\%[E2BIG]
|
|
The value of the given attribute is too large to fit into the buffer.
|
|
The integer that the
|
|
.I valuelength
|
|
argument points to has been modified to show the actual number
|
|
of bytes that would be required to store the value of that attribute.
|
|
.TP
|
|
.SM
|
|
\%[ENOENT]
|
|
The named file does not exist.
|
|
.TP
|
|
.SM
|
|
\%[EPERM]
|
|
The effective user
|
|
.SM ID
|
|
does not match the owner of the file
|
|
and the effective user
|
|
.SM ID
|
|
is not super-user.
|
|
.TP
|
|
.SM
|
|
\%[ENOTDIR]
|
|
A component of the
|
|
path prefix
|
|
is not a directory.
|
|
.TP
|
|
.SM
|
|
\%[EACCES]
|
|
Search permission is denied on a
|
|
component of the
|
|
path prefix.
|
|
.TP
|
|
.SM
|
|
\%[EINVAL]
|
|
A bit was set in the
|
|
.I flag
|
|
argument that is not defined for this system call.
|
|
.TP
|
|
.SM
|
|
\%[EFAULT]
|
|
.I Path,
|
|
.I attrname,
|
|
.I attrvalue,
|
|
or
|
|
.I valuelength
|
|
points outside the allocated address space of the process.
|
|
.TP
|
|
.SM
|
|
\%[ELOOP]
|
|
A path name lookup involved too many symbolic links.
|
|
.TP
|
|
.SM
|
|
\%[ENAMETOOLONG]
|
|
The length of
|
|
.I path
|
|
exceeds
|
|
.SM
|
|
.RI { MAXPATHLEN },
|
|
or a pathname component is longer than
|
|
.SM
|
|
.RI { MAXNAMELEN }.
|
|
.PP
|
|
.I attr_getf\^
|
|
will fail if:
|
|
.TP 15
|
|
.SM
|
|
\%[ENOATTR]
|
|
The attribute name given is not associated with the indicated
|
|
filesystem object.
|
|
.TP
|
|
.SM
|
|
\%[E2BIG]
|
|
The value of the given attribute is too large to fit into the buffer.
|
|
The integer that the
|
|
.I valuelength
|
|
argument points to has been modified to show the actual numnber
|
|
of bytes that would be required to store the value of that attribute.
|
|
.TP
|
|
.SM
|
|
\%[EINVAL]
|
|
A bit was set in the
|
|
.I flag
|
|
argument that is not defined for this system call,
|
|
or
|
|
.I fd\^
|
|
refers to a socket, not a file.
|
|
.TP
|
|
.SM
|
|
\%[EFAULT]
|
|
.I Attrname,
|
|
.I attrvalue,
|
|
or
|
|
.I valuelength
|
|
points outside the allocated address space of the process.
|
|
.TP
|
|
.SM
|
|
\%[EBADF]
|
|
.I Fd\^
|
|
does not refer to a valid descriptor.
|
|
.SH "SEE ALSO"
|
|
attr(1),
|
|
.br
|
|
attr_list(2), attr_listf(2)
|
|
.br
|
|
attr_multi(2), attr_multif(2)
|
|
.br
|
|
attr_remove(2), attr_removef(2),
|
|
.br
|
|
attr_set(2), attr_setf(2),
|
|
.SH "DIAGNOSTICS"
|
|
Upon successful completion, a value of 0 is returned.
|
|
Otherwise, a value of \-1 is returned and
|
|
.I errno\^
|
|
is set to indicate the error.
|
|
.\" @(#)attr_get.2 1.0 of 6.12.95
|
|
.Ee
|