перечислить имена пользовательских атрибутов объекта файловой системы (list the names of the user attributes of a filesystem object)
Имя (Name)
attr_list, attr_listf - list the names of the user attributes of
a filesystem object
Синопсис C (C Synopsis)
#include <attr/attributes.h>
int attr_list (const char ∗path, char ∗buffer,
const int buffersize, int flags,
attrlist_cursor_t ∗cursor);
int attr_listf (int fd, char ∗buffer,
const int buffersize, int flags,
attrlist_cursor_t ∗cursor);
Описание (Description)
The attr_list and attr_listf functions provide a way to list the
existing attributes of a filesystem object.
Path points to a path name for a filesystem object, and fd refers
to the file descriptor associated with a file. The buffer will
be filled with a structure describing at least a portion of the
attributes associated with the given filesystem object. Buffer
will be overwritten with an attrlist_t structure containing a
list of the attributes associated with that filesystem object, up
to a maximum of buffersize bytes. The buffer must be
sufficiently large to hold the appropriate data structures plus
at least one maximally sized attribute name, but cannot be more
than ATTR_MAX_VALUELEN (currently 64KB) bytes in length.
The contents of an attrlist_t structure include the following
members:
int32_t al_count; /∗ number of entries in attrlist ∗/
int32_t al_more; /∗ T/F: more attrs (do syscall again) ∗/
int32_t al_offset[1]; /∗ byte offsets of attrs [var-sized] ∗/
The al_count field shows the number of attributes represented in
this buffer, which is also the number of elements in the
al_offset array. The al_more field will be non-zero if another
attr_list call would result in more attributes. The al_offset
array contains the byte offset within the buffer of the structure
describing each of the attributes, an attrlist_ent_t structure.
The ATTR_ENTRY(buffer, index) macro will help with decoding the
list. It takes a pointer to the buffer and an index into the
al_offset array and returns a pointer to the corresponding
attrlist_ent_t structure.
The contents of an attrlist_ent_t structure include the following
members:
uint32_t a_valuelen; /∗ number bytes in value of attr ∗/
char a_name[]; /∗ attr name (NULL terminated) ∗/
The a_valuelen field shows the size in bytes of the value
associated with the attribute whose name is stored in the a_name
field. The name is a NULL terminated string.
Note that the value of the attribute cannot be obtained through
this interface, the attr_get call should be used to get the
value. The attr_list interface tells the calling process how
large of a buffer it must have in order to get the attribute´s
value.
The flags argument can contain the following symbols bitwise
OR´ed together:
ATTR_ROOT
List the attributes that are 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_list function call. The default is to follow
symbolic links.
The cursor argument is a pointer to an opaque data structure that
the kernel uses to track the calling process´s position in the
attribute list. The only valid operations on a cursor are to
pass it into an attr_list function call or to zero it out. It
should be zero´ed out before the first attr_list call. Note that
multi-threaded applications may keep more than one cursor in
order to serve multiple contexts, ie: the attr_list call is
"thread-safe".
attr_list 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 was set in the flag argument that is not defined for
this system call, or the buffer was too small or too
large.
[EFAULT]
Either Path or buffer points outside the allocated address
space of the process, or buffer or bufsize are not 32bit
aligned.
[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}.
[ENOATTR]
attribute does not exist for this file.
attr_listf will fail if:
[EINVAL]
A bit was set in the flag argument that is not defined for
this system call, or fd refers to a socket, not a file, or
the buffer was too small or too large.
[EFAULT]
Either Path or buffer points outside the allocated address
space of the process, or buffer or bufsize are not 32bit
aligned.
[EBADF]
Fd does not refer to a valid descriptor.
Диагностика (Diagnostic)
Upon successful completion, a value of 0 is returned. Otherwise,
a value of -1 is returned and errno is set to indicate the error.
Смотри также (See also)
attr(1), attr_multi(3), attr_remove(3), attr_set(3)
