Hi, On 2/14/2025 2:02 AM, Alexei Starovoitov wrote: > On Sat, Jan 25, 2025 at 2:59 AM Hou Tao <houtao@xxxxxxxxxxxxxxx> wrote: >> From: Hou Tao <houtao1@xxxxxxxxxx> >> >> For map with dynptr key support, it needs to use map_extra to specify >> the maximum data length of these dynptrs. The implementation of the map >> will check whether map_extra is smaller than the limitation imposed by >> memory allocation during map creation. It may also use map_extra to >> optimize the memory allocation for dynptr. > Why limit it? > The only piece of code I could find is: > > uptr->size > map->map_extra > > and it doesn't look necessary. > Let it consume whatever necessary ? > . It will be usable when trying to iterate keys through ->get_next_key() in kernel (e.g., support map_seq_show_elem in v3), because for now the data memory for dynptr in the map key is allocated by the caller (because the callee hold a rcu read lock). If the max length of dynptr data is unknown, map_iter_alloc()/map_seq_next() may need some logic to probe the max length of dynptr data during the traversal of keys. Will check whether or not it is feasible in v3.
