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    SubjectRe: [RFC PATCH v2] waitfd
    Casey Dahlin wrote:
    > Linux now exposes signals, timers, and events via file descriptors
    > through signalfd, timerfd, and eventfd. This means programmers can use a
    > single select/[e]poll call to monitor all change in their program. This
    > patch aims to expose child death via the same mechanism.
    >
    > waitfd provides a file descriptor out of which may be read a series of
    > siginfo_t objects describing child death. A child process is reaped as
    > soon as its information is read. This means child monitoring too can be
    > performed with that same poll call.
    >
    > Patch is against v2.6.28
    >
    > --CJD
    >
    > diff --git a/arch/x86/include/asm/unistd_32.h
    > b/arch/x86/include/asm/unistd_32.h
    > index f2bba78..134d83c 100644
    > --- a/arch/x86/include/asm/unistd_32.h
    > +++ b/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_waitfd 333
    >
    > #ifdef __KERNEL__
    >
    > diff --git a/arch/x86/include/asm/unistd_64.h
    > b/arch/x86/include/asm/unistd_64.h
    > index d2e415e..b28eb07 100644
    > --- a/arch/x86/include/asm/unistd_64.h
    > +++ b/arch/x86/include/asm/unistd_64.h
    > @@ -653,6 +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_waitfd 295
    > +__SYSCALL(__NR_waitfd, sys_waitfd)
    >

    Only for x86??

    >
    > #ifndef __NO_STUBS
    > diff --git a/arch/x86/kernel/syscall_table_32.S
    > b/arch/x86/kernel/syscall_table_32.S
    > index d44395f..c796a8b 100644
    > --- a/arch/x86/kernel/syscall_table_32.S
    > +++ b/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_waitfd
    > diff --git a/fs/Makefile b/fs/Makefile
    > index d9f8afe..74c31fb 100644
    > --- a/fs/Makefile
    > +++ b/fs/Makefile
    > @@ -25,6 +25,7 @@ obj-$(CONFIG_INOTIFY_USER) += inotify_user.o
    > obj-$(CONFIG_EPOLL) += eventpoll.o
    > obj-$(CONFIG_ANON_INODES) += anon_inodes.o
    > obj-$(CONFIG_SIGNALFD) += signalfd.o
    > +obj-$(CONFIG_WAITFD) += waitfd.o
    > obj-$(CONFIG_TIMERFD) += timerfd.o
    > obj-$(CONFIG_EVENTFD) += eventfd.o
    > obj-$(CONFIG_AIO) += aio.o
    > diff --git a/fs/waitfd.c b/fs/waitfd.c
    > new file mode 100644
    > index 0000000..0155a83
    > --- /dev/null
    > +++ b/fs/waitfd.c
    > @@ -0,0 +1,117 @@
    > +/*
    > + * fs/waitfd.c
    > + *
    > + * Copyright (C) 2008 Red Hat, Casey Dahlin <cdahlin@redhat.com>
    > + *
    > + * Largely derived from fs/signalfd.c
    > + */
    > +
    > +#include <linux/file.h>
    > +#include <linux/poll.h>
    > +#include <linux/init.h>
    > +#include <linux/fs.h>
    > +#include <linux/sched.h>
    > +#include <linux/kernel.h>
    > +#include <linux/signal.h>
    > +#include <linux/list.h>
    > +#include <linux/anon_inodes.h>
    > +#include <linux/syscalls.h>
    > +
    > +long do_waitid(int which, pid_t upid,
    > + struct siginfo __user *infop, int options,
    > + struct rusage __user *ru);
    > +
    > +struct waitfd_ctx {
    > + int ops;
    > + int which;
    > + pid_t upid;
    > +};
    > +

    Please use kernel coding style: use tabs to indent, not <lots-of-spaces>,
    and struct members, functions, etc., are indented by one tab stop minimum.

    > +static int waitfd_release(struct inode *inode, struct file *file)
    > +{
    > + kfree(file->private_data);
    > + return 0;
    > +}
    > +
    > +static unsigned int waitfd_poll(struct file *file, poll_table *wait)
    > +{
    > + struct waitfd_ctx *ctx = file->private_data;
    > + long value;
    > +
    > + poll_wait(file, &current->signal->wait_chldexit, wait);
    > +
    > + value = do_waitid(ctx->which, ctx->upid, NULL,
    > + ctx->ops | WNOHANG | WNOWAIT, NULL);
    > + if (value > 0 || value == -ECHILD)
    > + return POLLIN;
    > +
    > + return 0;
    > +}
    > +
    > +/*
    > + * Returns a multiple of the size of a struct siginfo, or a negative
    > + * error code. The "count" parameter must be at least sizeof(struct
    > siginfo)
    > + */
    > +static ssize_t waitfd_read(struct file *file, char __user *buf, size_t
    > count,
    > + loff_t *ppos)
    > +{
    > + struct waitfd_ctx *ctx = file->private_data;
    > + struct siginfo __user *info_addr = (struct siginfo *)buf;
    > + int flags = ctx->ops;
    > + ssize_t ret, total = 0;
    > +
    > + count /= sizeof(struct siginfo);
    > + if (!count)
    > + return -EINVAL;
    > +
    > + do {
    > + ret = do_waitid(ctx->which, ctx->upid, info_addr, flags, NULL);
    > + if (ret == 0)
    > + ret = -EAGAIN;
    > + if (ret == -ECHILD)
    > + ret = 0;
    > + if (ret <= 0)
    > + break;
    > +
    > + info_addr++;
    > + total += sizeof(struct siginfo);
    > + flags |= WNOHANG;
    > + } while (--count);
    > +
    > + return total ? total: ret;

    return total ? total : ret;
    please.

    > +}
    > +
    > +static const struct file_operations waitfd_fops = {
    > + .release = waitfd_release,
    > + .poll = waitfd_poll,
    > + .read = waitfd_read,
    > +};
    > +
    > +asmlinkage long sys_waitfd(int which, pid_t upid, int options, int unused)
    > +{
    > + int ufd;
    > + struct waitfd_ctx *ctx;
    > +
    > + /* Just to make sure we don't end up with a sys_waitfd4 */
    > + (void)unused;
    > +
    > + if (options & ~(WNOHANG|WEXITED|WSTOPPED|WCONTINUED))
    > + return -EINVAL;
    > + if (!(options & (WEXITED|WSTOPPED|WCONTINUED)))
    > + return -EINVAL;

    Use spaces around '|'.

    > +
    > + ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
    > + if (!ctx)
    > + return -ENOMEM;
    > +
    > + ctx->ops = options;
    > + ctx->upid = upid;
    > + ctx->which = which;
    > +
    > + ufd = anon_inode_getfd("[waitfd]", &waitfd_fops, ctx,
    > + (options & WNOHANG) ? O_NONBLOCK : 0);
    > + if (ufd < 0)
    > + kfree(ctx);
    > +
    > + return ufd;
    > +}
    > diff --git a/init/Kconfig b/init/Kconfig
    > index f763762..bc34871 100644
    > --- a/init/Kconfig
    > +++ b/init/Kconfig
    > @@ -683,6 +683,16 @@ config EPOLL
    > Disabling this option will cause the kernel to be built without
    > support for epoll family of system calls.
    >
    > +config WAITFD
    > + bool "Enable waitfd() system call" if EMBEDDED
    > + select ANON_INODES
    > + default y
    > + help
    > + Enable the waitfd() system call that allows receving child state

    receiving

    Kconfig help text should be indented by <tab><space><space>.

    > + changes from a file descriptor.
    > +
    > + If unsure, say Y.
    > +
    > config SIGNALFD
    > bool "Enable signalfd() system call" if EMBEDDED
    > select ANON_INODES
    > diff --git a/kernel/exit.c b/kernel/exit.c
    > index 2d8be7e..b53e8ba 100644
    > --- a/kernel/exit.c
    > +++ b/kernel/exit.c
    > @@ -1233,18 +1233,20 @@ static int wait_noreap_copyout(struct
    > task_struct *p, pid_t pid, uid_t uid,
    > int retval = rusagep ? getrusage(p, RUSAGE_BOTH, rusagep) : 0;
    >
    > put_task_struct(p);
    > - if (!retval)
    > - retval = put_user(SIGCHLD, &infop->si_signo);
    > - if (!retval)
    > - retval = put_user(0, &infop->si_errno);
    > - if (!retval)
    > - retval = put_user((short)why, &infop->si_code);
    > - if (!retval)
    > - retval = put_user(pid, &infop->si_pid);
    > - if (!retval)
    > - retval = put_user(uid, &infop->si_uid);
    > - if (!retval)
    > - retval = put_user(status, &infop->si_status);
    > + if (infop) {
    > + if (!retval)
    > + retval = put_user(SIGCHLD, &infop->si_signo);
    > + if (!retval)
    > + retval = put_user(0, &infop->si_errno);
    > + if (!retval)
    > + retval = put_user((short)why, &infop->si_code);
    > + if (!retval)
    > + retval = put_user(pid, &infop->si_pid);
    > + if (!retval)
    > + retval = put_user(uid, &infop->si_uid);
    > + if (!retval)
    > + retval = put_user(status, &infop->si_status);
    > + }
    > if (!retval)
    > retval = pid;
    > return retval;
    > @@ -1727,35 +1729,12 @@ repeat:
    > end:
    > current->state = TASK_RUNNING;
    > remove_wait_queue(&current->signal->wait_chldexit,&wait);
    > - if (infop) {
    > - if (retval > 0)
    > - retval = 0;
    > - else {
    > - /*
    > - * For a WNOHANG return, clear out all the fields
    > - * we would set so the user can easily tell the
    > - * difference.
    > - */
    > - if (!retval)
    > - retval = put_user(0, &infop->si_signo);
    > - if (!retval)
    > - retval = put_user(0, &infop->si_errno);
    > - if (!retval)
    > - retval = put_user(0, &infop->si_code);
    > - if (!retval)
    > - retval = put_user(0, &infop->si_pid);
    > - if (!retval)
    > - retval = put_user(0, &infop->si_uid);
    > - if (!retval)
    > - retval = put_user(0, &infop->si_status);
    > - }
    > - }
    > return retval;
    > }
    >
    > -asmlinkage long sys_waitid(int which, pid_t upid,
    > - struct siginfo __user *infop, int options,
    > - struct rusage __user *ru)
    > +long do_waitid(int which, pid_t upid,
    > + struct siginfo __user *infop, int options,
    > + struct rusage __user *ru)
    > {
    > struct pid *pid = NULL;
    > enum pid_type type;
    > @@ -1789,6 +1768,39 @@ asmlinkage long sys_waitid(int which, pid_t upid,
    > ret = do_wait(type, pid, options, infop, NULL, ru);
    > put_pid(pid);
    >
    > + return ret;
    > +}
    > +
    > +asmlinkage long sys_waitid(int which, pid_t upid,
    > + struct siginfo __user *infop, int options,
    > + struct rusage __user *ru)
    > +{
    > + long ret;
    > +
    > + ret = do_waitid(which, upid, infop, options, ru);
    > +
    > + if (ret > 0)
    > + ret = 0;
    > + else {
    > + /*
    > + * For a WNOHANG return, clear out all the fields
    > + * we would set so the user can easily tell the
    > + * difference.
    > + */
    > + if (!ret)
    > + ret = put_user(0, &infop->si_signo);
    > + if (!ret)
    > + ret = put_user(0, &infop->si_errno);
    > + if (!ret)
    > + ret = put_user(0, &infop->si_code);
    > + if (!ret)
    > + ret = put_user(0, &infop->si_pid);
    > + if (!ret)
    > + ret = put_user(0, &infop->si_uid);
    > + if (!ret)
    > + ret = put_user(0, &infop->si_status);
    > + }
    > +
    > /* avoid REGPARM breakage on x86: */
    > asmlinkage_protect(5, ret, which, upid, infop, options, ru);
    > return ret;
    > diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
    > index e14a232..e8d4da6 100644
    > --- a/kernel/sys_ni.c
    > +++ b/kernel/sys_ni.c
    > @@ -163,6 +163,7 @@ cond_syscall(sys_ioprio_set);
    > cond_syscall(sys_ioprio_get);
    >
    > /* New file descriptors */
    > +cond_syscall(sys_waitfd);
    > cond_syscall(sys_signalfd);
    > cond_syscall(sys_signalfd4);
    > cond_syscall(compat_sys_signalfd);


    --
    ~Randy


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