path: root/man/man3/attr_list.3

.TH ATTR_LIST 3
.SH NAME
attr_list, attr_listf \- list the names of the user attributes of a filesystem object
.SH C SYNOPSIS
.PP
.sp
.nf
.B #include <attr/attributes.h>
.sp
.B "int attr_list (const char \(**path, char \(**buffer, "
.B "               const int buffersize, int flags,"
.B "               attrlist_cursor_t \(**cursor);"
.PP
.B "int attr_listf (int fd, char \(**buffer, "
.B "                const int buffersize, int flags,"
.B "                attrlist_cursor_t \(**cursor);"
.Op
.SH DESCRIPTION
The
.I attr_list
and
.I attr_listf
functions provide a way to list the existing attributes of a
filesystem object.
.P
.I Path\^
points to a path name for a filesystem object, and 
.I fd\^
refers to the file descriptor associated with a file.
The 
.I buffer
will be filled with a structure describing at least a portion of the
attributes associated with the given filesystem object.
.I Buffer
will be overwritten with an \f4attrlist_t\fP structure
containing a list of the attributes associated with
that filesystem object, up to a maximum of
.I buffersize
bytes.
The 
.I 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.
.PP
.Op c p a
The contents of an \f4attrlist_t\fP structure include the following members:
.P
.RS 3
.nf
.ft 4
.ta 9n 22n
__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] \(**/
.ft 1
.fi
.RE
.PP
The
.I al_count
field shows the number of attributes represented in this buffer,
which is also the number of elements in the
.I al_offset
array.
The
.I al_more
field will be non-zero if another
.I attr_list
call would result in more attributes.
The
.I al_offset
array contains the byte offset within the
.I buffer
of the structure describing each of the attributes,
an \f4attrlist_ent_t\fP structure.
The \f4ATTR_ENTRY(buffer, index)\fP macro will help with decoding the list.
It takes a pointer to the
.I buffer
and an
.I index
into the 
.I al_offset
array and returns a pointer to the corresponding
\f4attrlist_ent_t\fP structure.
.PP
The contents of an \f4attrlist_ent_t\fP structure
include the following members:
.P
.RS 3
.nf
.ft 4
.ta 9n 22n
u_int32_t a_valuelen; /\(** number bytes in value of attr \(**/
char a_name[]; /\(** attr name (NULL terminated) \(**/
.ft 1
.fi
.Op
.RE
.PP
The
.I a_valuelen
field shows the size in bytes of the value
associated with the attribute whose name is stored in the
.I a_name
field.
The name is a NULL terminated string.
.PP
Note that the value of the attribute cannot be obtained through
this interface, the
.I attr_get
call should be used to get the value.
The
.I attr_list
interface tells the calling process how large of a buffer
it must have in order to get the attribute\'s value.
.PP
The
.I flags
argument can contain the following symbols bitwise OR\'ed together:
.TP
.SM
\%ATTR_ROOT
List the attributes that are in the
.B root
address space, not in the
.B user
address space.
(limited to use by super-user only)
.TP
.SM
\%ATTR_DONTFOLLOW
Do not follow symbolic links when resolving a
.I path
on an
.I attr_list
function call.
The default is to follow symbolic links.
.PP
The
.I 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
.I cursor
are to pass it into an
.I attr_list
function call or to zero it out.
It should be zero\'ed out before the first
.I attr_list
call.
Note that multi-threaded applications may keep more than one
.I cursor
in order to serve multiple contexts, ie: the
.I attr_list
call is "thread-safe".
.PP
.I attr_list
will fail if one or more of the following are true:
.TP 17
.SM
\%[ENOENT]
The named file does not exist.
.TP
.SM
\%[EPERM]
The effective user
.SM ID
does not match the owner of the file
and the effective user
.SM ID
is not super-user.
.TP
.SM
\%[ENOTDIR]
A component of the
path prefix
is not a directory.
.TP
.SM
\%[EACCES]
Search permission is denied on a
component of the
path prefix.
.TP
.SM
\%[EINVAL]
A bit was set in the
.I flag
argument that is not defined for this system call,
or the buffer was too small or too large.
.TP
.SM
\%[EFAULT]
Either
.I Path
or
.I buffer
points outside the allocated address space of the process, or
.I buffer
or
.I bufsize
are not 32bit aligned.
.TP
.SM
\%[ELOOP]
A path name lookup involved too many symbolic links.
.TP
.SM
\%[ENAMETOOLONG]
The length of
.I path
exceeds
.SM
.RI { MAXPATHLEN },
or a pathname component is longer than
.SM
.RI { MAXNAMELEN }.
.TP
.SM
\%[ENOATTR] 
.I attribute\^
does not exist for this file.
.PP
.I attr_listf\^
will fail if:
.TP 15
.SM
\%[EINVAL]
A bit was set in the
.I flag
argument that is not defined for this system call, or
.I fd\^
refers to a socket, not a file,
or the buffer was too small or too large.
.TP
.SM
\%[EFAULT]
Either
.I Path
or
.I buffer
points outside the allocated address space of the process, or
.I buffer
or
.I bufsize
are not 32bit aligned.
.TP
.SM
\%[EBADF]
.I Fd\^
does not refer to a valid descriptor.
.SH "SEE ALSO"
attr(1),
.br
attrctl(2),
.br
attr_get(3), attr_getf(3),
.br
attr_multi(3), attr_multif(3)
.br
attr_remove(3), attr_removef(3),
.br
attr_set(3), attr_set(3)
.SH "DIAGNOSTICS"
Upon successful completion, a value of 0 is returned.
Otherwise, a value of \-1 is returned and
.I errno\^
is set to indicate the error.