The return value of the completion will be 0 on success, negative
error code on failure.
@param io the context to operate in
@param oid the name of the object
@param completion what to do when the append is safe and complete
@param buf the data to append
@param len length of buf (in bytes)
@returns 0 on success, -EROFS if the io context specifies a snap_seq
other than LIBRADOS_SNAP_HEAD
Asychronously append data to an object
Queues the append and returns.
The return value of the completion will be 0 on success, negative error code on failure.
@param io the context to operate in @param oid the name of the object @param completion what to do when the append is safe and complete @param buf the data to append @param len length of buf (in bytes) @returns 0 on success, -EROFS if the io context specifies a snap_seq other than LIBRADOS_SNAP_HEAD