NAME
attr_multi, attr_multif - manipulate multiple user attributes on a
filesystem object at once
C SYNOPSIS
#include <attr/attributes.h>
int attr_multi (const char *path, attr_multiop_t *oplist,
int count, int flags);
int attr_multif (int fd, attr_multiop_t *oplist,
int count, int flags);
DESCRIPTION
The attr_multi and attr_multif functions provide a way to operate on
multiple attributes of a filesystem object at once.
Path points to a path name for a filesystem object, and fd refers to
the file descriptor associated with a file. The oplist is an array of
attr_multiop_t structures. Each element in that array describes a
single attribute operation and provides all the information required to
carry out that operation and to check for success or failure of that
operation. Count tells how many elements are in the oplist array.
The contents of an attr_multiop_t structure include the following
members:
int am_opcode; /* which operation to perform (see below) */
int am_error; /* [out arg] result of this sub-op (an errno) */
char *am_attrname; /* attribute name to work with */
char *am_attrvalue; /* [in/out arg] attribute value (raw bytes) */
int am_length; /* [in/out arg] length of value */
int am_flags; /* flags (bit-wise OR of #defines below) */
The am_opcode field defines how the remaining fields are to be
interpreted and can take on one of the following values:
ATTR_OP_GET /* return the indicated attr’s value */
ATTR_OP_SET /* set/create the indicated attr/value pair */
ATTR_OP_REMOVE /* remove the indicated attr */
The am_error field will contain the appropriate error result code if
that sub-operation fails. The result codes for a given sub-operation
are a subset of the result codes that are possible from the
corresponding single-attribute function call. For example, the result
code possible from an ATTR_OP_GET sub-operation are a subset of those
that can be returned from an attr_get function call.
The am_attrname field is a pointer to a NULL terminated string giving
the attribute name that the sub-operation should operate on.
The am_attrvalue, am_length and am_flags fields are used to store the
value of the named attribute, and some control flags for that sub-
operation, respectively. Their use varies depending on the value of
the am_opcode field.
ATTR_OP_GET
The am_attrvalue field is a pointer to a empty buffer that will
be overwritten with the value of the named attribute. The
am_length field is initially the total size of the memory buffer
that the am_attrvalue field points to. After the operation, the
am_length field contains the actual size of the attribute´s
value. The am_flags field may be set to the ATTR_ROOT flag. If
the process has appropriate priviledges, the ROOT namespace will
be searched for the named attribute, otherwise the USER
namespace will be searched.
ATTR_OP_SET
The am_attrvalue and am_length fields contain the new value for
the given attribute name and its length. The ATTR_ROOT flag may
be set in the am_flags field. If the process has appropriate
priviledges, the ROOT namespace will be searched for the named
attribute, otherwise the USER namespace will be searched. The
ATTR_CREATE and the ATTR_REPLACE flags may also be set in the
am_flags field (but not simultaneously). If the ATTR_CREATE
flag is set, the sub-operation will set the am_error field to
EEXIST if the named attribute already exists. If the
ATTR_REPLACE flag is set, the sub-operation will set the
am_error field to ENOATTR if the named attribute does not
already exist. If neither of those two flags are set and the
attribute does not exist, then the attribute will be created
with the given value. If neither of those two flags are set and
the attribute already exists, then the value will be replaced
with the given value.
ATTR_OP_REMOVE
The am_attrvalue and am_length fields are not used and are
ignored. The am_flags field may be set to the ATTR_ROOT flag.
If the process has appropriate priviledges, the ROOT namespace
will be searched for the named attribute, otherwise the USER
namespace will be searched.
The flags argument to the attr_multi call is used to control following
of symbolic links in the path argument. The default is to follow
symbolic links, flags should be set to ATTR_DONTFOLLOW to not follow
symbolic links.
attr_multi will fail if one or more of the following are true:
[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 other than ATTR_DONTFOLLOW was set in the flag
argument.
[EFAULT] Path, or oplist 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_multif will fail if:
[EINVAL] A bit was set in the flag argument, or fd refers to a
socket, not a file.
[EFAULT] Oplist points outside the allocated address space of the
process.
[EBADF] Fd does not refer to a valid descriptor.
DIAGNOSTICS
On success, zero is returned. On error, -1 is returned, and errno is
set appropriately. Note that the individual operations listed in the
oplist array each have their own error return fields. The errno
variable only records the result of the attr_multi call itself, not the
result of any of the sub-operations.
SEE ALSO
attr(1), attr_get(3), attr_list(3), attr_remove(3), and attr_set(3).