#include <sys/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); [
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.
[c p a] 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; /* 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:
u_int32_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:
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:
attr_listf will fail if: