Re: [patch 1/2][RFC] add socketat syscall

Michael Kerrisk wrote:

quoted

On Fri, Oct 31, 2008 at 4:56 PM, Daniel Lezcano [off-list ref] wrote:

quoted

This patch adds the socketat syscall which allows to specify in
which network namespace we want to create a socket. The network
namespace destination is referred by a socket fd previously opened
in the destination network namespace.

Daniel,

Is there any documentation for this system call, and/or test programs?

Not yet.

This small patch is a proposition to Andreas and Vivien to have a single 
process being able to manage several network namespaces.

When a process unshares the network, it creates a socket which is used 
as a socket control (it belongs to the network namespace). Each time a 
network namespace is created, a socket control is created.

When the process has to create a socket for a specific network 
namespace, it can use the socket control to specify it. This is the 
purpose of the socketat syscall.

One example for a program in userspace:

int main(int argc, char *argv[])
{
	const int maxunshare = 128;
	int scs[maxunshare];
	int i, fd;
	
	for (i = 0; i < maxunshare; i++) {
		scs[i] = socket(PF_INET, SOCK_DGRAM, 0);
		unshare(CLONE_NEWNET);
	}

	....

	/* I want to create a socket inside the network namespace #10 */

	fd = socketat(scs[10], PF_INET, SOCKET_STREAM, 0);

	....

	bind, listen, etc ...
}

quoted

quoted

Signed-off-by: Daniel Lezcano <dlezcano-NmTC/0ZBporQT0dZR+AlfA@public.gmane.org>
---
 arch/x86/include/asm/unistd_32.h   |    1
 arch/x86/include/asm/unistd_64.h   |    3 +-
 arch/x86/kernel/syscall_table_32.S |    1
 include/linux/syscalls.h           |    1
 kernel/sys_ni.c                    |    1
 net/socket.c                       |   45 +++++++++++++++++++++++++++++++++++++
 6 files changed, 51 insertions(+), 1 deletion(-)

Index: net-next-2.6/arch/x86/include/asm/unistd_32.h
===================================================================

--- net-next-2.6.orig/arch/x86/include/asm/unistd_32.h
+++ net-next-2.6/arch/x86/include/asm/unistd_32.h

@@ -338,6 +338,7 @@
 #define __NR_dup3              330
 #define __NR_pipe2             331
 #define __NR_inotify_init1     332
+#define __NR_socketat           333

 #ifdef __KERNEL__

Index: net-next-2.6/arch/x86/include/asm/unistd_64.h
===================================================================

--- net-next-2.6.orig/arch/x86/include/asm/unistd_64.h
+++ net-next-2.6/arch/x86/include/asm/unistd_64.h

@@ -653,7 +653,8 @@ __SYSCALL(__NR_dup3, sys_dup3)
 __SYSCALL(__NR_pipe2, sys_pipe2)
 #define __NR_inotify_init1                     294
 __SYSCALL(__NR_inotify_init1, sys_inotify_init1)
-
+#define __NR_socketat                           295
+__SYSCALL(__NR_socketat, sys_socketat)

 #ifndef __NO_STUBS
 #define __ARCH_WANT_OLD_READDIR

Index: net-next-2.6/arch/x86/kernel/syscall_table_32.S
===================================================================

--- net-next-2.6.orig/arch/x86/kernel/syscall_table_32.S
+++ net-next-2.6/arch/x86/kernel/syscall_table_32.S

@@ -332,3 +332,4 @@ ENTRY(sys_call_table)
       .long sys_dup3                  /* 330 */
       .long sys_pipe2
       .long sys_inotify_init1
+       .long sys_socketat

Index: net-next-2.6/net/socket.c
===================================================================

--- net-next-2.6.orig/net/socket.c
+++ net-next-2.6/net/socket.c

@@ -1253,6 +1253,51 @@ out_release:
       return retval;
 }

+asmlinkage long sys_socketat(int fd, int family, int type, int protocol)
+{
+       int retval, fput_needed;
+       struct socket *sock;
+       struct socket *sockat;
+       struct net *net;
+       int flags;
+
+       /* Check the SOCK_* constants for consistency.  */
+       BUILD_BUG_ON(SOCK_CLOEXEC != O_CLOEXEC);
+       BUILD_BUG_ON((SOCK_MAX | SOCK_TYPE_MASK) != SOCK_TYPE_MASK);
+       BUILD_BUG_ON(SOCK_CLOEXEC & SOCK_TYPE_MASK);
+       BUILD_BUG_ON(SOCK_NONBLOCK & SOCK_TYPE_MASK);
+
+       flags = type & ~SOCK_TYPE_MASK;
+       if (flags & ~(SOCK_CLOEXEC | SOCK_NONBLOCK))
+               return -EINVAL;
+       type &= SOCK_TYPE_MASK;
+
+       if (SOCK_NONBLOCK != O_NONBLOCK && (flags & SOCK_NONBLOCK))
+               flags = (flags & ~SOCK_NONBLOCK) | O_NONBLOCK;
+
+       sock = sockfd_lookup_light(fd, &retval, &fput_needed);
+       if (!sock)
+               goto out;
+
+       net = sock_net(sock->sk);
+
+       retval = __sock_create(net, family, type, protocol, &sockat, 0);
+       if (retval)
+               goto out_fput;
+
+       retval = sock_map_fd(sock, flags & (O_CLOEXEC | O_NONBLOCK));
+       if (retval < 0)
+               goto out_release;
+out_fput:
+       fput_light(sock->file, fput_needed);
+out:
+       return retval;
+
+out_release:
+       sock_release(sockat);
+       goto out;
+}
+
 /*
 *     Create a pair of connected sockets.
 */

Index: net-next-2.6/include/linux/syscalls.h
===================================================================

--- net-next-2.6.orig/include/linux/syscalls.h
+++ net-next-2.6/include/linux/syscalls.h

@@ -423,6 +423,7 @@ asmlinkage long sys_recvfrom(int, void _
                               struct sockaddr __user *, int __user *);
 asmlinkage long sys_recvmsg(int fd, struct msghdr __user *msg, unsigned flags);
 asmlinkage long sys_socket(int, int, int);
+asmlinkage long sys_socketat(int, int, int, int);
 asmlinkage long sys_socketpair(int, int, int, int __user *);
 asmlinkage long sys_socketcall(int call, unsigned long __user *args);
 asmlinkage long sys_listen(int, int);

Index: net-next-2.6/kernel/sys_ni.c
===================================================================

--- net-next-2.6.orig/kernel/sys_ni.c
+++ net-next-2.6/kernel/sys_ni.c

@@ -40,6 +40,7 @@ cond_syscall(sys_send);
 cond_syscall(sys_recvfrom);
 cond_syscall(sys_recv);
 cond_syscall(sys_socket);
+cond_syscall(sys_socketat);
 cond_syscall(sys_setsockopt);
 cond_syscall(compat_sys_setsockopt);
 cond_syscall(sys_getsockopt);

--

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