This patch adds preadv and pwritev system calls. These syscalls are a
pretty straightforward combination of pread and readv (same for write).
They are quite useful for doing vectored I/O in threaded applications.
Using lseek+readv instead opens race windows you'll have to plug with
locking.
Other systems have such system calls too, for example NetBSD, check
here: http://www.daemon-systems.org/man/preadv.2.html
The application-visible interface provided by glibc should look like
this to be compatible to the existing implementations in the *BSD family:
ssize_t preadv(int d, const struct iovec *iov, int iovcnt, off_t offset);
ssize_t pwritev(int d, const struct iovec *iov, int iovcnt, off_t offset);
This prototype has one problem though: On 32bit archs is the (64bit)
offset argument unaligned, which the syscall ABI of several archs doesn't
allow to do. At least s390 needs a wrapper in glibc to handle this. As
we'll need a wrappers in glibc anyway I've decided to push problem to
glibc entriely and use a syscall prototype which works without
arch-specific wrappers inside the kernel: The offset argument is
explicitly splitted into two 32bit values.
The patch sports the actual system call implementation and the windup in
the x86 system call tables. Other archs follow as separate patches.
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: <linux-api@vger.kernel.org>
Cc: <linux-arch@vger.kernel.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Introduce a new accept4() system call. The addition of this system call
matches analogous changes in 2.6.27 (dup3(), evenfd2(), signalfd4(),
inotify_init1(), epoll_create1(), pipe2()) which added new system calls
that differed from analogous traditional system calls in adding a flags
argument that can be used to access additional functionality.
The accept4() system call is exactly the same as accept(), except that
it adds a flags bit-mask argument. Two flags are initially implemented.
(Most of the new system calls in 2.6.27 also had both of these flags.)
SOCK_CLOEXEC causes the close-on-exec (FD_CLOEXEC) flag to be enabled
for the new file descriptor returned by accept4(). This is a useful
security feature to avoid leaking information in a multithreaded
program where one thread is doing an accept() at the same time as
another thread is doing a fork() plus exec(). More details here:
http://udrepper.livejournal.com/20407.html "Secure File Descriptor Handling",
Ulrich Drepper).
The other flag is SOCK_NONBLOCK, which causes the O_NONBLOCK flag
to be enabled on the new open file description created by accept4().
(This flag is merely a convenience, saving the use of additional calls
fcntl(F_GETFL) and fcntl (F_SETFL) to achieve the same result.
Here's a test program. Works on x86-32. Should work on x86-64, but
I (mtk) don't have a system to hand to test with.
It tests accept4() with each of the four possible combinations of
SOCK_CLOEXEC and SOCK_NONBLOCK set/clear in 'flags', and verifies
that the appropriate flags are set on the file descriptor/open file
description returned by accept4().
I tested Ulrich's patch in this thread by applying against 2.6.28-rc2,
and it passes according to my test program.
/* test_accept4.c
Copyright (C) 2008, Linux Foundation, written by Michael Kerrisk
<mtk.manpages@gmail.com>
Licensed under the GNU GPLv2 or later.
*/
#define _GNU_SOURCE
#include <unistd.h>
#include <sys/syscall.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <stdlib.h>
#include <fcntl.h>
#include <stdio.h>
#include <string.h>
#define PORT_NUM 33333
#define die(msg) do { perror(msg); exit(EXIT_FAILURE); } while (0)
/**********************************************************************/
/* The following is what we need until glibc gets a wrapper for
accept4() */
/* Flags for socket(), socketpair(), accept4() */
#ifndef SOCK_CLOEXEC
#define SOCK_CLOEXEC O_CLOEXEC
#endif
#ifndef SOCK_NONBLOCK
#define SOCK_NONBLOCK O_NONBLOCK
#endif
#ifdef __x86_64__
#define SYS_accept4 288
#elif __i386__
#define USE_SOCKETCALL 1
#define SYS_ACCEPT4 18
#else
#error "Sorry -- don't know the syscall # on this architecture"
#endif
static int
accept4(int fd, struct sockaddr *sockaddr, socklen_t *addrlen, int flags)
{
printf("Calling accept4(): flags = %x", flags);
if (flags != 0) {
printf(" (");
if (flags & SOCK_CLOEXEC)
printf("SOCK_CLOEXEC");
if ((flags & SOCK_CLOEXEC) && (flags & SOCK_NONBLOCK))
printf(" ");
if (flags & SOCK_NONBLOCK)
printf("SOCK_NONBLOCK");
printf(")");
}
printf("\n");
#if USE_SOCKETCALL
long args[6];
args[0] = fd;
args[1] = (long) sockaddr;
args[2] = (long) addrlen;
args[3] = flags;
return syscall(SYS_socketcall, SYS_ACCEPT4, args);
#else
return syscall(SYS_accept4, fd, sockaddr, addrlen, flags);
#endif
}
/**********************************************************************/
static int
do_test(int lfd, struct sockaddr_in *conn_addr,
int closeonexec_flag, int nonblock_flag)
{
int connfd, acceptfd;
int fdf, flf, fdf_pass, flf_pass;
struct sockaddr_in claddr;
socklen_t addrlen;
printf("=======================================\n");
connfd = socket(AF_INET, SOCK_STREAM, 0);
if (connfd == -1)
die("socket");
if (connect(connfd, (struct sockaddr *) conn_addr,
sizeof(struct sockaddr_in)) == -1)
die("connect");
addrlen = sizeof(struct sockaddr_in);
acceptfd = accept4(lfd, (struct sockaddr *) &claddr, &addrlen,
closeonexec_flag | nonblock_flag);
if (acceptfd == -1) {
perror("accept4()");
close(connfd);
return 0;
}
fdf = fcntl(acceptfd, F_GETFD);
if (fdf == -1)
die("fcntl:F_GETFD");
fdf_pass = ((fdf & FD_CLOEXEC) != 0) ==
((closeonexec_flag & SOCK_CLOEXEC) != 0);
printf("Close-on-exec flag is %sset (%s); ",
(fdf & FD_CLOEXEC) ? "" : "not ",
fdf_pass ? "OK" : "failed");
flf = fcntl(acceptfd, F_GETFL);
if (flf == -1)
die("fcntl:F_GETFD");
flf_pass = ((flf & O_NONBLOCK) != 0) ==
((nonblock_flag & SOCK_NONBLOCK) !=0);
printf("nonblock flag is %sset (%s)\n",
(flf & O_NONBLOCK) ? "" : "not ",
flf_pass ? "OK" : "failed");
close(acceptfd);
close(connfd);
printf("Test result: %s\n", (fdf_pass && flf_pass) ? "PASS" : "FAIL");
return fdf_pass && flf_pass;
}
static int
create_listening_socket(int port_num)
{
struct sockaddr_in svaddr;
int lfd;
int optval;
memset(&svaddr, 0, sizeof(struct sockaddr_in));
svaddr.sin_family = AF_INET;
svaddr.sin_addr.s_addr = htonl(INADDR_ANY);
svaddr.sin_port = htons(port_num);
lfd = socket(AF_INET, SOCK_STREAM, 0);
if (lfd == -1)
die("socket");
optval = 1;
if (setsockopt(lfd, SOL_SOCKET, SO_REUSEADDR, &optval,
sizeof(optval)) == -1)
die("setsockopt");
if (bind(lfd, (struct sockaddr *) &svaddr,
sizeof(struct sockaddr_in)) == -1)
die("bind");
if (listen(lfd, 5) == -1)
die("listen");
return lfd;
}
int
main(int argc, char *argv[])
{
struct sockaddr_in conn_addr;
int lfd;
int port_num;
int passed;
passed = 1;
port_num = (argc > 1) ? atoi(argv[1]) : PORT_NUM;
memset(&conn_addr, 0, sizeof(struct sockaddr_in));
conn_addr.sin_family = AF_INET;
conn_addr.sin_addr.s_addr = htonl(INADDR_LOOPBACK);
conn_addr.sin_port = htons(port_num);
lfd = create_listening_socket(port_num);
if (!do_test(lfd, &conn_addr, 0, 0))
passed = 0;
if (!do_test(lfd, &conn_addr, SOCK_CLOEXEC, 0))
passed = 0;
if (!do_test(lfd, &conn_addr, 0, SOCK_NONBLOCK))
passed = 0;
if (!do_test(lfd, &conn_addr, SOCK_CLOEXEC, SOCK_NONBLOCK))
passed = 0;
close(lfd);
exit(passed ? EXIT_SUCCESS : EXIT_FAILURE);
}
[mtk.manpages@gmail.com: rewrote changelog, updated test program]
Signed-off-by: Ulrich Drepper <drepper@redhat.com>
Tested-by: Michael Kerrisk <mtk.manpages@gmail.com>
Acked-by: Michael Kerrisk <mtk.manpages@gmail.com>
Cc: <linux-api@vger.kernel.org>
Cc: <linux-arch@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Change header guards named "ASM_X86__*" to "_ASM_X86_*" since:
a. the double underscore is ugly and pointless.
b. no leading underscore violates namespace constraints.
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Gerd Hoffmann