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Date: Sat, 17 Mar 2007 22:35:08 +0100
From: Arnd Bergmann <arnd@...db.de>
To: Davide Libenzi <davidel@...ilserver.org>
Cc: Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Oleg Nesterov <oleg@...sign.ru>
Subject: Re: [patch 2/13] signal/timer/event fds v6 - signalfd core ...
On Friday 16 March 2007 01:22:15 Davide Libenzi wrote:
> +
> +static struct sighand_struct *signalfd_get_sighand(struct signalfd_ctx
> *ctx, + unsigned long *flags);
> +static void signalfd_put_sighand(struct signalfd_ctx *ctx,
> + struct sighand_struct *sighand,
> + unsigned long *flags);
> +static void signalfd_cleanup(struct signalfd_ctx *ctx);
> +static int signalfd_close(struct inode *inode, struct file *file);
> +static unsigned int signalfd_poll(struct file *file, poll_table *wait);
> +static int signalfd_copyinfo(struct signalfd_siginfo __user *uinfo,
> + siginfo_t const *kinfo);
> +static ssize_t signalfd_read(struct file *file, char __user *buf, size_t
> count, + loff_t *ppos);
> +
see my comment about forward declarations in the previous mail
> +asmlinkage long sys_signalfd(int ufd, sigset_t __user *user_mask, size_t
> sizemask) +{
> + int error;
> + unsigned long flags;
> + sigset_t sigmask;
> + struct signalfd_ctx *ctx;
> + struct sighand_struct *sighand;
> + struct file *file;
> + struct inode *inode;
> +
> + error = -EINVAL;
> + if (sizemask != sizeof(sigset_t) ||
> + copy_from_user(&sigmask, user_mask, sizeof(sigmask)))
> + goto err_exit;
sizeof(sigset_t) may be different for native and 32-bit compat code.
It would be good if you could handle sizemask==4 && sizeof(sigset_t)==8
in this code, so that there is no need for an extra compat_sys_signalfd
function.
> + if ((sighand = signalfd_get_sighand(ctx, &flags)) != NULL) {
> + if (next_signal(&ctx->tsk->pending, &ctx->sigmask) > 0 ||
> + next_signal(&ctx->tsk->signal->shared_pending,
> + &ctx->sigmask) > 0)
> + events |= POLLIN;
> + signalfd_put_sighand(ctx, sighand, &flags);
> + } else
> + events |= POLLIN;
> +
> + return events;
> +}
I never really understood the events mask, but other subsystems often
use (POLLIN | POLLRDNORM) instead of just POLLIN. Is there a reason
for not returning POLLRDNORM here?
> +static int signalfd_copyinfo(struct signalfd_siginfo __user *uinfo,
> + siginfo_t const *kinfo)
> +{
> + long err;
> +
> + err = __clear_user(uinfo, sizeof(*uinfo));
> +
> + /*
> + * If you change siginfo_t structure, please be sure
> + * this code is fixed accordingly.
> + */
> + err |= __put_user(kinfo->si_signo, &uinfo->signo);
> + err |= __put_user(kinfo->si_errno, &uinfo->err);
> + err |= __put_user((short)kinfo->si_code, &uinfo->code);
> + switch (kinfo->si_code & __SI_MASK) {
> + case __SI_KILL:
> + err |= __put_user(kinfo->si_pid, &uinfo->pid);
> + err |= __put_user(kinfo->si_uid, &uinfo->uid);
> + break;
> + case __SI_TIMER:
> + err |= __put_user(kinfo->si_tid, &uinfo->tid);
> + err |= __put_user(kinfo->si_overrun, &uinfo->overrun);
> + err |= __put_user(kinfo->si_ptr, &uinfo->svptr);
> + break;
> + case __SI_POLL:
> + err |= __put_user(kinfo->si_band, &uinfo->band);
> + err |= __put_user(kinfo->si_fd, &uinfo->fd);
> + break;
> + case __SI_FAULT:
> + err |= __put_user(kinfo->si_addr, &uinfo->addr);
> +#ifdef __ARCH_SI_TRAPNO
> + err |= __put_user(kinfo->si_trapno, &uinfo->trapno);
> +#endif
> + break;
> + case __SI_CHLD:
> + err |= __put_user(kinfo->si_pid, &uinfo->pid);
> + err |= __put_user(kinfo->si_uid, &uinfo->uid);
> + err |= __put_user(kinfo->si_status, &uinfo->status);
> + err |= __put_user(kinfo->si_utime, &uinfo->utime);
> + err |= __put_user(kinfo->si_stime, &uinfo->stime);
> + break;
> + case __SI_RT: /* This is not generated by the kernel as of now. */
> + case __SI_MESGQ: /* But this is */
> + err |= __put_user(kinfo->si_pid, &uinfo->pid);
> + err |= __put_user(kinfo->si_uid, &uinfo->uid);
> + err |= __put_user(kinfo->si_ptr, &uinfo->svptr);
> + break;
> + default: /* this is just in case for now ... */
> + err |= __put_user(kinfo->si_pid, &uinfo->pid);
> + err |= __put_user(kinfo->si_uid, &uinfo->uid);
> + break;
> + }
> +
> + return err ? -EFAULT: sizeof(*uinfo);
> +}
Doing it this way looks rather inefficient to me. I think it's
better to just prepare the signalfd_siginfo on the stack and
do a single copy_to_user.
Also, what's the reasoning behind defining a new structure
instead of just returning siginfo_t? Sure siginfo_t is ugly
but it is a well-defined structure and users already deal
with the problems it causes.
> +static void __exit signalfd_exit(void)
> +{
> + kmem_cache_destroy(signalfd_ctx_cachep);
> +}
> +
> +module_init(signalfd_init);
> +module_exit(signalfd_exit);
> +
> +MODULE_LICENSE("GPL");
Since this file defines a syscall, it can't be a module, so why bother
with this?
> +
> +struct signalfd_siginfo {
> + __u32 signo;
> + __s32 err;
> + __s32 code;
> + __u32 pid;
> + __u32 uid;
> + __s32 fd;
> + __u32 tid;
> + __u32 band;
> + __u32 overrun;
> + __u32 trapno;
> + __s32 status;
> + __s32 svint;
> + __u64 svptr;
> + __u64 utime;
> + __u64 stime;
> + __u64 addr;
> +};
> +
Since you define the structure using __u32 etc types, I assume
you mean it to be included from libc or other user space, right?
In this case it needs to be listed in include/linux/Kbuild for
make headers_install to work.
> +void signalfd_deliver(struct task_struct *tsk, int sig);
> +
> +/*
> + * No need to fall inside signalfd_deliver() if no signal listeners are
> available. + */
> +static inline void signalfd_notify(struct task_struct *tsk, int sig)
> +{
> + if (unlikely(!list_empty(&tsk->sighand->sfdlist)))
> + signalfd_deliver(tsk, sig);
> +}
> +
> +static inline void signalfd_detach_locked(struct task_struct *tsk)
> +{
> + if (unlikely(!list_empty(&tsk->sighand->sfdlist)))
> + signalfd_deliver(tsk, -1);
> +}
> +
> +static inline void signalfd_detach(struct task_struct *tsk)
> +{
> + struct sighand_struct *sighand = tsk->sighand;
> +
> + if (unlikely(!list_empty(&sighand->sfdlist))) {
> + spin_lock_irq(&sighand->siglock);
> + signalfd_deliver(tsk, -1);
> + spin_unlock_irq(&sighand->siglock);
> + }
> +}
> +
And all of these need to be surrounded by #ifdef __KERNEL__ so
they don't bleed out to the user space visible parts.
Arnd <><
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