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Subject[PATCH 13/18] flag parameters: NONBLOCK in socket and socketpair
This patch introduces support for the SOCK_NONBLOCK flag in socket,
socketpair, and paccept. To do this the internal function sock_attach_fd
gets an additional parameter which it uses to set the appropriate flag for
the file descriptor.

Given that in modern, scalable programs almost all socket connections are
non-blocking and the minimal additional cost for the new functionality
I see no reason not to add this code.

The following test must be adjusted for architectures other than x86 and
x86-64 and in case the syscall numbers changed.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
#include <fcntl.h>
#include <pthread.h>
#include <stdio.h>
#include <unistd.h>
#include <netinet/in.h>
#include <sys/socket.h>
#include <sys/syscall.h>

#ifndef __NR_paccept
# ifdef __x86_64__
# define __NR_paccept 288
# elif defined __i386__
# define SYS_PACCEPT 18
# define USE_SOCKETCALL 1
# else
# error "need __NR_paccept"
# endif
#endif

#ifdef USE_SOCKETCALL
# define paccept(fd, addr, addrlen, mask, flags) \
({ long args[6] = { \
(long) fd, (long) addr, (long) addrlen, (long) mask, 8, (long) flags }; \
syscall (__NR_socketcall, SYS_PACCEPT, args); })
#else
# define paccept(fd, addr, addrlen, mask, flags) \
syscall (__NR_paccept, fd, addr, addrlen, mask, 8, flags)
#endif

#define PORT 57392

#define SOCK_NONBLOCK 0x20000000

static pthread_barrier_t b;

static void *
tf (void *arg)
{
pthread_barrier_wait (&b);
int s = socket (AF_INET, SOCK_STREAM, 0);
struct sockaddr_in sin;
sin.sin_family = AF_INET;
sin.sin_addr.s_addr = htonl (INADDR_LOOPBACK);
sin.sin_port = htons (PORT);
connect (s, (const struct sockaddr *) &sin, sizeof (sin));
close (s);
pthread_barrier_wait (&b);

pthread_barrier_wait (&b);
s = socket (AF_INET, SOCK_STREAM, 0);
sin.sin_port = htons (PORT);
connect (s, (const struct sockaddr *) &sin, sizeof (sin));
close (s);
pthread_barrier_wait (&b);

return NULL;
}

int
main (void)
{
int fd;
fd = socket (PF_INET, SOCK_STREAM, 0);
if (fd == -1)
{
puts ("socket(0) failed");
return 1;
}
int fl = fcntl (fd, F_GETFL);
if (fl == -1)
{
puts ("fcntl failed");
return 1;
}
if (fl & O_NONBLOCK)
{
puts ("socket(0) set non-blocking mode");
return 1;
}
close (fd);

fd = socket (PF_INET, SOCK_STREAM|SOCK_NONBLOCK, 0);
if (fd == -1)
{
puts ("socket(SOCK_NONBLOCK) failed");
return 1;
}
fl = fcntl (fd, F_GETFL);
if (fl == -1)
{
puts ("fcntl failed");
return 1;
}
if ((fl & O_NONBLOCK) == 0)
{
puts ("socket(SOCK_NONBLOCK) does not set non-blocking mode");
return 1;
}
close (fd);

int fds[2];
if (socketpair (PF_UNIX, SOCK_STREAM, 0, fds) == -1)
{
puts ("socketpair(0) failed");
return 1;
}
for (int i = 0; i < 2; ++i)
{
fl = fcntl (fds[i], F_GETFL);
if (fl == -1)
{
puts ("fcntl failed");
return 1;
}
if (fl & O_NONBLOCK)
{
printf ("socketpair(0) set non-blocking mode for fds[%d]\n", i);
return 1;
}
close (fds[i]);
}

if (socketpair (PF_UNIX, SOCK_STREAM|SOCK_NONBLOCK, 0, fds) == -1)
{
puts ("socketpair(SOCK_NONBLOCK) failed");
return 1;
}
for (int i = 0; i < 2; ++i)
{
fl = fcntl (fds[i], F_GETFL);
if (fl == -1)
{
puts ("fcntl failed");
return 1;
}
if ((fl & O_NONBLOCK) == 0)
{
printf ("socketpair(SOCK_NONBLOCK) does not set non-blocking mode for fds[%d]\n", i);
return 1;
}
close (fds[i]);
}

pthread_barrier_init (&b, NULL, 2);

struct sockaddr_in sin;
pthread_t th;
if (pthread_create (&th, NULL, tf, NULL) != 0)
{
puts ("pthread_create failed");
return 1;
}

int s = socket (AF_INET, SOCK_STREAM, 0);
int reuse = 1;
setsockopt (s, SOL_SOCKET, SO_REUSEADDR, &reuse, sizeof (reuse));
sin.sin_family = AF_INET;
sin.sin_addr.s_addr = htonl (INADDR_LOOPBACK);
sin.sin_port = htons (PORT);
bind (s, (struct sockaddr *) &sin, sizeof (sin));
listen (s, SOMAXCONN);

pthread_barrier_wait (&b);

int s2 = paccept (s, NULL, 0, NULL, 0);
if (s2 < 0)
{
puts ("paccept(0) failed");
return 1;
}

fl = fcntl (s2, F_GETFL);
if (fl & O_NONBLOCK)
{
puts ("paccept(0) set non-blocking mode");
return 1;
}
close (s2);
close (s);

pthread_barrier_wait (&b);

s = socket (AF_INET, SOCK_STREAM, 0);
sin.sin_port = htons (PORT);
setsockopt (s, SOL_SOCKET, SO_REUSEADDR, &reuse, sizeof (reuse));
bind (s, (struct sockaddr *) &sin, sizeof (sin));
listen (s, SOMAXCONN);

pthread_barrier_wait (&b);

s2 = paccept (s, NULL, 0, NULL, SOCK_NONBLOCK);
if (s2 < 0)
{
puts ("paccept(SOCK_NONBLOCK) failed");
return 1;
}

fl = fcntl (s2, F_GETFL);
if ((fl & O_NONBLOCK) == 0)
{
puts ("paccept(SOCK_NONBLOCK) does not set non-blocking mode");
return 1;
}
close (s2);
close (s);

pthread_barrier_wait (&b);
puts ("OK");

return 0;
}
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


include/linux/net.h | 1 +
net/socket.c | 13 +++++++------
2 files changed, 8 insertions(+), 6 deletions(-)


Signed-off-by: Ulrich Drepper <drepper@redhat.com>

diff --git a/include/linux/net.h b/include/linux/net.h
index 71f7dd5..fcd3694 100644
--- a/include/linux/net.h
+++ b/include/linux/net.h
@@ -94,6 +94,7 @@ enum sock_type {
SOCK_PACKET = 10,

/* Flag values, ORed to the types above. */
+ SOCK_NONBLOCK = 0x20000000,
SOCK_CLOEXEC = 0x40000000
};

diff --git a/net/socket.c b/net/socket.c
index 66c4a8c..1df03ae 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -367,7 +367,7 @@ static int sock_alloc_fd(struct file **filep)
return fd;
}

-static int sock_attach_fd(struct socket *sock, struct file *file)
+static int sock_attach_fd(struct socket *sock, struct file *file, int flags)
{
struct dentry *dentry;
struct qstr name = { .name = "" };
@@ -389,20 +389,20 @@ static int sock_attach_fd(struct socket *sock, struct file *file)
init_file(file, sock_mnt, dentry, FMODE_READ | FMODE_WRITE,
&socket_file_ops);
SOCK_INODE(sock)->i_fop = &socket_file_ops;
- file->f_flags = O_RDWR;
+ file->f_flags = O_RDWR | (flags & O_NONBLOCK);
file->f_pos = 0;
file->private_data = sock;

return 0;
}

int sock_map_fd(struct socket *sock, int flags)
{
struct file *newfile;
int fd = sock_alloc_fd(&newfile, flags);

if (likely(fd >= 0)) {
- int err = sock_attach_fd(sock, newfile);
+ int err = sock_attach_fd(sock, newfile, flags);

if (unlikely(err < 0)) {
put_filp(newfile);
@@ -1216,6 +1216,7 @@ int sock_create_kern(int family, int type, int protocol, struct socket **res)

static const struct flags_rmap sock_file_flags_remap[] = {
{ SOCK_CLOEXEC, O_CLOEXEC },
+ { SOCK_NONBLOCK, O_NONBLOCK }
};

asmlinkage long sys_socket(int family, int type, int protocol)
@@ -1292,12 +1293,12 @@ asmlinkage long sys_socketpair(int family, int type, int protocol,
goto out_release_both;
}

- err = sock_attach_fd(sock1, newfile1);
+ err = sock_attach_fd(sock1, newfile1, fflags);
if (unlikely(err < 0)) {
goto out_fd2;
}

- err = sock_attach_fd(sock2, newfile2);
+ err = sock_attach_fd(sock2, newfile2, fflags);
if (unlikely(err < 0)) {
fput(newfile1);
goto out_fd1;
@@ -1456,7 +1457,7 @@ long do_accept(int fd, struct sockaddr __user *upeer_sockaddr,
goto out_put;
}

- err = sock_attach_fd(newsock, newfile);
+ err = sock_attach_fd(newsock, newfile, fflags);
if (err < 0)
goto out_fd_simple;


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