CEPH_RADOS_API int rados_read(rados_ioctx_t io, const char * oid, char * buf, size_t len, uint64_t off)¶
Read data from an object
The io context determines the snapshot to read from, if any was set by rados_ioctx_snap_set_read().
Return
number of bytes read on success, negative error code on failure
Parameters
io: the context in which to perform the read
oid: the name of the object to read from
buf: where to store the results
len: the number of bytes to read
off: the offset to start reading from in the object
librados c同步读取功能询问要读取多少个字节，而没有显式的功能来读取整个对象。
如果我想读取对象的所有字节，则可以给它提供一个巨大的size_t值，假设到达对象末尾时它将被切断吗？还是会继续阅读？
在需要读取对象或将其存储在对象的元数据中之前，我可以确保知道对象的大小，但是如果可能的话，尽量避免执行那些不必要的步骤。