Re: [PATCH 0/5] add initial io_uring_cmd support for sockets

[Pavel Begunkov <asml.silence@gmail.com>]

On 5/2/23 10:21, Adrien Delorme wrote:
>  From Adrien Delorme
> 
>> From: David Ahern
>> Sent: 12 April 2023 7:39
>>> Sent: 11 April 2023 16:28
>> ....
>>> Christoph's patch set a few years back that removed set_fs broke the
>>> ability to do in-kernel ioctl and {s,g}setsockopt calls. I did not
>>> follow that change; was it a deliberate intent to not allow these
>>> in-kernel calls vs wanting to remove the set_fs? e.g., can we add a
>>> kioctl variant for in-kernel use of the APIs?
>>
>> I think that was a side effect, and with no in-tree in-kernel
>> users (apart from limited calls in bpf) it was deemed acceptable.
>> (It is a PITA for any code trying to use SCTP in kernel.)
>>
>> One problem is that not all sockopt calls pass the correct length.
>> And some of them can have very long buffers.
>> Not to mention the ones that are read-modify-write.
>>
>> A plausible solution is to pass a 'fat pointer' that contains
>> some, or all, of:
>>        - A userspace buffer pointer.
>>        - A kernel buffer pointer.
>>        - The length supplied by the user.
>>        - The length of the kernel buffer.
>>        = The number of bytes to copy on completion.
>> For simple user requests the syscall entry/exit code
>> would copy the data to a short on-stack buffer.
>> Kernel users just pass the kernel address.
>> Odd requests can just use the user pointer.
>>
>> Probably needs accessors that add in an offset.
>>
>> It might also be that some of the problematic sockopt
>> were in decnet - now removed.
> 
> Hello everyone,
> 
> I'm currently working on an implementation of {get,set} sockopt.
> Since this thread is already talking about it, I hope that I replying at the correct place.

Hi Adrien, I believe Breno is working on set/getsockopt as well
and had similar patches for awhile, but that would need for some
problems to be solved first, e.g. try and decide whether it copies
to a ptr as the syscall versions or would get/return optval
directly in sqe/cqe. And also where to store bits that you pass
in struct args_setsockopt_uring, and whether to rely on SQE128
or not.


> My implementation is rather simple using a struct that will be used to pass the necessary info throught sqe->cmd.
> 
> Here is my implementation based of kernel version 6.3 :
> 
> Signed-off-by: Adrien Delorme <delorme.ade@outlook.com>
> 
> diff -uprN a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
> --- a/include/uapi/linux/io_uring.h     2023-04-23 15:02:52.000000000 -0400
> +++ b/include/uapi/linux/io_uring.h     2023-04-24 07:55:21.406981696 -0400
> @@ -235,6 +235,25 @@ enum io_uring_op {
>    */
> #define IORING_URING_CMD_FIXED (1U << 0)
> 
> +/* struct io_uring_cmd->cmd_op flags for socket operations */
> +#define IO_URING_CMD_OP_GETSOCKOPT 0x0
> +#define IO_URING_CMD_OP_SETSOCKOPT 0x1
> +
> +/* Struct to pass args for IO_URING_CMD_OP_GETSOCKOPT and IO_URING_CMD_OP_SETSOCKOPT operations */
> +struct args_setsockopt_uring{

The name of the structure is quite inconsistent with the
rest. It's better to be io_[uring_]_sockopt_arg or some
variation.

> +       int                             level;
> +       int                     optname;
> +       char __user *   user_optval;
> +       int                     optlen;

That's uapi, there should not be __user, and field sizes
should be more portable, i.e. use __u32, __u64, etc, look
through the file.

Would need to look into the get/setsockopt implementation
before saying anything about uring_cmd_{set,get}sockopt.


> +};
> +
> +struct args_getsockopt_uring{
> +       int                             level;
> +       int                     optname;
> +       char __user *   user_optval;
> +       int      __user *       optlen;
> +};
> +
> 
> /*
>    * sqe->fsync_flags
> diff -uprN a/net/socket.c b/net/socket.c
> --- a/net/socket.c      2023-04-23 15:02:52.000000000 -0400
> +++ b/net/socket.c      2023-04-24 08:06:44.800981696 -0400
> @@ -108,6 +108,11 @@
> #include <linux/ptp_clock_kernel.h>
> #include <trace/events/sock.h>
> 
> +#ifdef CONFIG_IO_URING
> +#include <uapi/linux/io_uring.h>
> +#include <linux/io_uring.h>
> +#endif
> +
> #ifdef CONFIG_NET_RX_BUSY_POLL
> unsigned int sysctl_net_busy_read __read_mostly;
> unsigned int sysctl_net_busy_poll __read_mostly;
> @@ -132,6 +137,11 @@ static ssize_t sock_splice_read(struct f
>                                  struct pipe_inode_info *pipe, size_t len,
>                                  unsigned int flags);
> 
> +
> +#ifdef CONFIG_IO_URING
> +int socket_uring_cmd_handler(struct io_uring_cmd *cmd, unsigned int flags);
> +#endif
> +
> #ifdef CONFIG_PROC_FS
> static void sock_show_fdinfo(struct seq_file *m, struct file *f)
> {
> @@ -166,6 +176,9 @@ static const struct file_operations sock
>          .splice_write = generic_splice_sendpage,
>          .splice_read =  sock_splice_read,
>          .show_fdinfo =  sock_show_fdinfo,
> +#ifdef CONFIG_IO_URING
> +       .uring_cmd = socket_uring_cmd_handler,
> +#endif
> };
> 
> static const char * const pf_family_names[] = {
> @@ -2330,6 +2343,126 @@ SYSCALL_DEFINE5(getsockopt, int, fd, int
>          return __sys_getsockopt(fd, level, optname, optval, optlen);
> }
> 
> +#ifdef CONFIG_IO_URING
> +
> +/*
> + * Make getsockopt operation with io_uring.
> + * This fonction is based of the __sys_getsockopt without sockfd_lookup_light
> + * since io_uring retrieves it for us.
> + */
> +int uring_cmd_getsockopt(struct socket *sock, int level, int optname, char __user *optval,
> +               int __user *optlen)
> +{
> +       int err;
> +       int max_optlen;
> +
> +       err = security_socket_getsockopt(sock, level, optname);
> +       if (err)
> +               goto out_put;
> +
> +       if (!in_compat_syscall())
> +               max_optlen = BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN(optlen);
> +
> +       if (level == SOL_SOCKET)
> +               err = sock_getsockopt(sock, level, optname, optval, optlen);
> +       else if (unlikely(!sock->ops->getsockopt))
> +               err = -EOPNOTSUPP;
> +       else
> +               err = sock->ops->getsockopt(sock, level, optname, optval,
> +                                           optlen);
> +
> +       if (!in_compat_syscall())
> +               err = BPF_CGROUP_RUN_PROG_GETSOCKOPT(sock->sk, level, optname,
> +                                                    optval, optlen, max_optlen,
> +                                                    err);
> +out_put:
> +       return err;
> +}
> +
> +/*
> + * Make setsockopt operation with io_uring.
> + * This fonction is based of the __sys_setsockopt without sockfd_lookup_light
> + * since io_uring retrieves it for us.
> + */
> +int uring_cmd_setsockopt(struct socket *sock, int level, int optname, char *user_optval,
> +               int optlen)
> +{
> +       sockptr_t optval = USER_SOCKPTR(user_optval);
> +       char *kernel_optval = NULL;
> +       int err;
> +
> +       if (optlen < 0)
> +               return -EINVAL;
> +
> +       err = security_socket_setsockopt(sock, level, optname);
> +       if (err)
> +               goto out_put;
> +
> +       if (!in_compat_syscall())
> +               err = BPF_CGROUP_RUN_PROG_SETSOCKOPT(sock->sk, &level, &optname,
> +                                                    user_optval, &optlen,
> +                                                    &kernel_optval);
> +       if (err < 0)
> +               goto out_put;
> +       if (err > 0) {
> +               err = 0;
> +               goto out_put;
> +       }
> +
> +       if (kernel_optval)
> +               optval = KERNEL_SOCKPTR(kernel_optval);
> +       if (level == SOL_SOCKET && !sock_use_custom_sol_socket(sock))
> +               err = sock_setsockopt(sock, level, optname, optval, optlen);
> +       else if (unlikely(!sock->ops->setsockopt))
> +               err = -EOPNOTSUPP;
> +       else
> +               err = sock->ops->setsockopt(sock, level, optname, optval,
> +                                           optlen);
> +       kfree(kernel_optval);
> +out_put:
> +       return err;
> +}
> +
> +/*
> + * Handler uring_cmd socket file_operations.
> + *
> + * Operation code and struct are defined in /include/uapi/linux/io_uring.h
> + * The io_uring ring needs to be set with the flags : IORING_SETUP_SQE128 and IORING_SETUP_CQE32
> + *
> + */
> +int socket_uring_cmd_handler(struct io_uring_cmd *cmd, unsigned int flags){
> +
> +       /* Retrieve socket */
> +       struct socket *sock = sock_from_file(cmd->file);
> +
> +       if (!sock)
> +               return -EINVAL;
> +
> +       /* Does the requested operation */
> +       switch (cmd->cmd_op) {
> +               case IO_URING_CMD_OP_GETSOCKOPT:
> +                       struct args_getsockopt_uring *values_get = (struct args_getsockopt_uring *) cmd->cmd;
> +                       return uring_cmd_getsockopt(sock,
> +                                                                               values_get->level,
> +                                                                               values_get->optname,
> +                                                                               values_get->user_optval,
> +                                                                               values_get->optlen);
> +
> +               case IO_URING_CMD_OP_SETSOCKOPT:
> +                       struct args_setsockopt_uring *values_set = (struct args_setsockopt_uring *) cmd->cmd;
> +                       return uring_cmd_setsockopt(sock,
> +                                                                               values_set->level,
> +                                                                               values_set->optname,
> +                                                                               values_set->user_optval,
> +                                                                               values_set->optlen);
> +               default:
> +                       break;
> +
> +       }
> +       return -EINVAL;
> +}
> +#endif
> +
> /*
>    *     Shutdown a socket.
>    */
> 
> I would appreciate any feedback or advice you may have on this work. Hopefully it will be of some kind of help. Thank you for your time and consideration.
> 
> Adrien

-- 
Pavel Begunkov