одновременно управлять несколькими пользовательскими атрибутами объекта файловой системы (manipulate multiple user attributes on a filesystem object at once)
Имя (Name)
attr_multi, attr_multif - manipulate multiple user attributes on
a filesystem object at once
Синопсис C (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);
Описание (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.
Диагностика (Diagnostic)
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.
Смотри также (See also)
attr(1), attr_get(3), attr_list(3), attr_remove(3), attr_set(3)
