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 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.
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.