ATTR_SET(2)ATTR_SET(2)NAME
attr_set, attr_setf - set the value of a user attribute of a filesystem
object
C SYNOPSIS
#include <sys/attributes.h>
int attr_set (const char *path, const char *attrname,
const char *attrvalue, const int valuelength,
int flags);
int attr_setf (int fd, const char *attrname,
const char *attrvalue, const int valuelength,
int flags);
OVERVIEW
The attr group of system calls implement the ability for a user to attach
name/value pairs to objects within the filesystem.
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.
The 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.
The values can be up to ATTR_MAX_VALUELEN (currently 64KB) of arbitrary
binary data.
Attributes can be attached to all types of inodes: regular files,
directories, symbolic links, device nodes, etc.
There are 2 disjoint attribute name spaces associated with every
filesystem object. They are the root and user address spaces. The root
address space is accessible only to privileged users, and only then by
specifying a flag argument to the function call. A privileged user can
be either the superuser in an IRIX environment, or a user with
CAP_DEVICE_MGT capability. Other users will not see or be able to modify
attributes in the root address space. The 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.
Attributes are currently fully supported only in the XFS, CXFS and UDF
filesystem types. Other filesystem types may provide a partial
implementation.
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ATTR_SET(2)ATTR_SET(2)DESCRIPTION
The attr_set and attr_setf functions provide a way to create attributes
and set/change their values.
Path points to a path name for a filesystem object, and fd refers to the
file descriptor associated with a file. If the attribute attrname does
not exist, an attribute with the given name and value will be created and
associated with that indicated filesystem object. If an attribute with
that name already exists on that filesystem object, the existing value is
replaced with the new value given in this call. The new attribute value
is copied from the attrvalue buffer for a total of valuelength bytes.
The flags argument can contain the following symbols bitwise OR'ed
together:
ATTR_ROOT
Look for attrname in the root address space, not in the user address
space. (limited to use by super-user only)
ATTR_DONTFOLLOW
Do not follow symbolic links when resolving a path on an attr_set
function call. The default is to follow symbolic links.
ATTR_CREATE
Return an error (EEXIST) if an attribute of the given name already
exists on the indicated filesystem object, otherwise create an
attribute with the given name and value. This flag is used to
implement a pure create operation, without this flag attr_set will
create the attribute if it does not already exist. An error
(EINVAL) will be returned if both ATTR_CREATE and ATTR_REPLACE are
set in the same call.
ATTR_REPLACE
Return an error (ENOATTR) if an attribute of the given name does not
already exist on the indicated filesystem object, otherwise replace
the existing attribute's value with the given value. This flag is
used to implement a pure replacement operation, without this flag
attr_set will create the attribute if it does not already exist. An
error (EINVAL) will be returned if both ATTR_CREATE and ATTR_REPLACE
are set in the same call.
attr_set will fail if one or more of the following are true:
[ENOATTR] The attribute name given is not associated with the
indicated filesystem object and the ATTR_REPLACE flag
bit was set.
[E2BIG] The value of the given attribute is too large, it
exceeds the maximum allowable size of an attribute
value.
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ATTR_SET(2)ATTR_SET(2)
[EEXIST] The attribute name given is already associated with the
indicated filesystem object and the ATTR_CREATE flag bit
was set.
[ENOENT] The named file does not exist.
[EPERM] The effective user ID does not match the owner of the
file and the effective user ID is not super-user.
[ENOTDIR] A component of the path prefix is not a directory.
[EACCES] Search permission is denied on a component of the path
prefix.
[EINVAL] A bit was set in the flag argument that is not defined
for this system call, or both the ATTR_CREATE and
ATTR_REPLACE flags bits were set.
[EFAULT] Path, attrname, or attrvalue points outside the
allocated address space of the process.
[ELOOP] A path name lookup involved too many symbolic links.
[ENAMETOOLONG] The length of path exceeds {MAXPATHLEN}, or a pathname
component is longer than {MAXNAMELEN}.
attr_setf will fail if:
[ENOATTR] The attribute name given is not associated with the
indicated filesystem object and the ATTR_REPLACE flag bit
was set.
[E2BIG] The value of the given attribute is too large, it exceeds
the maximum allowable size of an attribute value.
[EEXIST] The attribute name given is already associated with the
indicated filesystem object and the ATTR_CREATE flag bit
was set.
[EINVAL] A bit was set in the flag argument that is not defined for
this system call, or both the ATTR_CREATE and ATTR_REPLACE
flags bits were set, or fd refers to a socket, not a file.
[EFAULT] Attrname, or attrvalue points outside the allocated
address space of the process.
[EBADF] Fd does not refer to a valid descriptor.
SEE ALSOattr(1),
attr_get(2), attr_getf(2),
attr_list(2), attr_listf(2)
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ATTR_SET(2)ATTR_SET(2)attr_multi(2), attr_multif(2)attr_remove(2), attr_removef(2),
DIAGNOSTICS
Upon successful completion, a value of 0 is returned. Otherwise, a value
of -1 is returned and errno is set to indicate the error.
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