On Thu, Aug 30, 2018 at 10:10 PM Willem de Bruijn willemdebruijn.kernel@gmail.com wrote:
On Wed, Aug 29, 2018 at 9:05 AM Arnd Bergmann arnd@arndb.de wrote:
The SIOCGSTAMP/SIOCGSTAMPNS ioctl commands are implemented by many socket protocol handlers, and all of those end up calling the same sock_get_timestamp()/sock_get_timestampns() helper functions, which results in a lot of duplicate code.
With the introduction of 64-bit time_t on 32-bit architectures, this gets worse, as we then need four different ioctl commands in each socket protocol implementation.
To simplify that, let's add a new .gettstamp() operation in struct proto_ops, and move ioctl implementation into the common sock_ioctl()/compat_sock_ioctl_trans() functions that these all go through.
We can reuse the sock_get_timestamp() implementation, but generalize it so it can deal with both native and compat mode, as well as timeval and timespec structures.
Signed-off-by: Arnd Bergmann arnd@arndb.de
This also will simplify fixing a recently reported race condition with sock_get_timestamp [1]. That calls sock_enable_timestamp, which modifies sk->sk_flags, without taking the socket lock. Currently some callers of sock_get_timestamp hold the lock (ax25, netrom, qrtr), many don't. See also how this patch removes the lock_sock in the netrom case. Moving the call to sock_gettstamp outside the protocol handlers will allow taking the lock inside the function.
I suppose it would be best to always take that lock then, rather than removing the lock as my patch does at the moment.
If this is the only valid implementation of .gettstamp, the indirect call could be avoided in favor of a simple branch.
I thought about that as well, but I could not come up with a good way to encode the difference between socket protocols that allow timestamping and those that don't.
I think ideally we would just call sock_gettstamp() unconditonally on every socket, and have that function decide whether timestamps make sense or not. The part I did not understand is which ones actually want the timestamps or not. Most protocols that implement the ioctls also assign skb->tstamp, but there are some protocols in which I could not see skb->tstamp ever being set, and some that set it but don't seem to have the ioctls.
Looking at it again, it seems that sock_gettstamp() should actually deal with this gracefully: it will return a -EINVAL error condition if the timestamp remains at the SK_DEFAULT_STAMP initial value, which is probably just as appropriate (or better) as the current -ENOTTY default, and if we are actually recording timestamps, we might just as well report them.
Acked-by: Willem de Bruijn willemb@google.com
Thanks,
Arnd