attr_multi, attr_multif - manipulate multiple user attributes on a filesystem
object at once
#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);
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 privileges, 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 privileges, 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 privileges, 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.
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.
attr(1),
attr_get(3),
attr_list(3),
attr_remove(3),
attr_set(3)