<p dir="ltr"><br>
On Jan 30, 2013 8:05 AM, "Andrey Vagin" <<a href="mailto:avagin@openvz.org">avagin@openvz.org</a>> wrote:<br>
><br>
> If signalfd is created with the flag SFD_PEEK, it reads siginfo-s<br>
> without dequeuing signals.<br>
><br>
> For reading not first siginfo pread(fd, buf, size, pos) can be used,<br>
> where ppos / sizeof(signalfd_siginfo) is a sequence number of a signal<br>
> in a queue.</p>
<p dir="ltr">Andrey,</p>
<p dir="ltr">Is it perhaps worth erroring (EINVAL) if ((ppos % sizeof (signalfd_siginfo)) != 0) ?</p>
<p dir="ltr">Cheers,</p>
<p dir="ltr">Michael</p>
<p dir="ltr">> This functionality is required for checkpointing pending signals.<br>
><br>
> v2: * signals can be dumped only from one queue.<br>
> * treat pos as offset in bytes, not in elements, so pos should be<br>
> aligned to the size of signalfd_siginfo.<br>
><br>
> Cc: Oleg Nesterov <<a href="mailto:oleg@redhat.com">oleg@redhat.com</a>><br>
> Cc: Alexander Viro <<a href="mailto:viro@zeniv.linux.org.uk">viro@zeniv.linux.org.uk</a>><br>
> Cc: "Paul E. McKenney" <<a href="mailto:paulmck@linux.vnet.ibm.com">paulmck@linux.vnet.ibm.com</a>><br>
> Cc: David Howells <<a href="mailto:dhowells@redhat.com">dhowells@redhat.com</a>><br>
> Cc: Dave Jones <<a href="mailto:davej@redhat.com">davej@redhat.com</a>><br>
> Cc: Andrey Vagin <<a href="mailto:avagin@openvz.org">avagin@openvz.org</a>><br>
> Cc: Michael Kerrisk <<a href="mailto:mtk.manpages@gmail.com">mtk.manpages@gmail.com</a>><br>
> Cc: Pavel Emelyanov <<a href="mailto:xemul@parallels.com">xemul@parallels.com</a>><br>
> CC: Cyrill Gorcunov <<a href="mailto:gorcunov@openvz.org">gorcunov@openvz.org</a>><br>
> Signed-off-by: Andrey Vagin <<a href="mailto:avagin@openvz.org">avagin@openvz.org</a>><br>
> ---<br>
> fs/signalfd.c | 61 ++++++++++++++++++++++++++++++++++++++++---<br>
> include/uapi/linux/signalfd.h | 2 ++<br>
> 2 files changed, 60 insertions(+), 3 deletions(-)<br>
><br>
> diff --git a/fs/signalfd.c b/fs/signalfd.c<br>
> index 8019ec9..0da6a30 100644<br>
> --- a/fs/signalfd.c<br>
> +++ b/fs/signalfd.c<br>
> @@ -51,6 +51,47 @@ struct signalfd_ctx {<br>
> sigset_t sigmask;<br>
> };<br>
><br>
> +static int peek_signal(struct sigpending *pending, sigset_t *mask,<br>
> + siginfo_t *info, loff_t *pseq)<br>
> +{<br>
> + struct sigqueue *q;<br>
> + int ret = 0;<br>
> +<br>
> + spin_lock_irq(&current->sighand->siglock);<br>
> +<br>
> + list_for_each_entry(q, &pending->list, list) {<br>
> + if (sigismember(mask, q->info.si_signo))<br>
> + continue;<br>
> +<br>
> + if ((*pseq)-- == 0) {<br>
> + copy_siginfo(info, &q->info);<br>
> + ret = info->si_signo;<br>
> + break;<br>
> + }<br>
> + }<br>
> +<br>
> + spin_unlock_irq(&current->sighand->siglock);<br>
> +<br>
> + return ret;<br>
> +}<br>
> +<br>
> +static ssize_t signalfd_peek(struct signalfd_ctx *ctx,<br>
> + siginfo_t *info, loff_t *ppos, int queue_mask)<br>
> +{<br>
> + loff_t seq = *ppos / sizeof(struct signalfd_siginfo);<br>
> + int signr = 0;<br>
> +<br>
> + if (queue_mask & SIGQUEUE_PRIVATE)<br>
> + signr = peek_signal(&current->pending,<br>
> + &ctx->sigmask, info, &seq);<br>
> + else if (queue_mask & SIGQUEUE_SHARED)<br>
> + signr = peek_signal(&current->signal->shared_pending,<br>
> + &ctx->sigmask, info, &seq);<br>
> + (*ppos) += sizeof(struct signalfd_siginfo);<br>
> +<br>
> + return signr;<br>
> +}<br>
> +<br>
> static int signalfd_release(struct inode *inode, struct file *file)<br>
> {<br>
> kfree(file->private_data);<br>
> @@ -257,9 +298,15 @@ static ssize_t signalfd_read(struct file *file, char __user *buf, size_t count,<br>
> if (!count)<br>
> return -EINVAL;<br>
><br>
> + if (*ppos % sizeof(struct signalfd_siginfo))<br>
> + return -EINVAL;<br>
> +<br>
> siginfo = (struct signalfd_siginfo __user *) buf;<br>
> do {<br>
> - ret = signalfd_dequeue(ctx, &info, nonblock, qmask);<br>
> + if (file->f_flags & SFD_PEEK)<br>
> + ret = signalfd_peek(ctx, &info, ppos, qmask);<br>
> + else<br>
> + ret = signalfd_dequeue(ctx, &info, nonblock, qmask);<br>
><br>
> if (unlikely(ret <= 0))<br>
> break;<br>
> @@ -315,7 +362,12 @@ SYSCALL_DEFINE4(signalfd4, int, ufd, sigset_t __user *, user_mask,<br>
> BUILD_BUG_ON(SFD_CLOEXEC != O_CLOEXEC);<br>
> BUILD_BUG_ON(SFD_NONBLOCK != O_NONBLOCK);<br>
><br>
> - if (flags & ~(SFD_CLOEXEC | SFD_NONBLOCK | SFD_RAW | SFD_QUEUES))<br>
> + if (flags & ~(SFD_CLOEXEC | SFD_NONBLOCK |<br>
> + SFD_RAW | SFD_PEEK | SFD_QUEUES))<br>
> + return -EINVAL;<br>
> +<br>
> + /* SFD_PEEK can be used for one queue only */<br>
> + if ((flags & SFD_PEEK) && ((flags & SFD_QUEUES) == SFD_QUEUES))<br>
> return -EINVAL;<br>
><br>
> if (sizemask != sizeof(sigset_t) ||<br>
> @@ -352,7 +404,10 @@ SYSCALL_DEFINE4(signalfd4, int, ufd, sigset_t __user *, user_mask,<br>
> }<br>
><br>
> file->f_flags |= (flags & SFD_QUEUES) ? : SFD_QUEUES;<br>
> - file->f_flags |= flags & SFD_RAW;<br>
> + file->f_flags |= flags & (SFD_RAW | SFD_PEEK);<br>
> +<br>
> + if (file->f_flags & SFD_PEEK)<br>
> + file->f_mode |= FMODE_PREAD;<br>
><br>
> fd_install(ufd, file);<br>
> } else {<br>
> diff --git a/include/uapi/linux/signalfd.h b/include/uapi/linux/signalfd.h<br>
> index 481b658..24c5d2d 100644<br>
> --- a/include/uapi/linux/signalfd.h<br>
> +++ b/include/uapi/linux/signalfd.h<br>
> @@ -20,6 +20,8 @@<br>
> #define SFD_SHARED_QUEUE O_DIRECTORY<br>
> /* Read signals from a per-thread queue */<br>
> #define SFD_PER_THREAD_QUEUE O_EXCL<br>
> +/* Read signals without removing them from a queue */<br>
> +#define SFD_PEEK O_APPEND<br>
><br>
> struct signalfd_siginfo {<br>
> __u32 ssi_signo;<br>
> --<br>
> 1.7.11.7<br>
><br>
</p>