lkml.org 
[lkml]   [2013]   [Jan]   [22]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH 3/3] signalfd: add ability to read siginfo-s without dequeuing signals
Date
If signalfd is created with the flag SFD_PEEK, it reads siginfo-s
without dequeuing signals.

For reading not first siginfo pread(fd, buf, size, pos) can be used,
where ppos is a sequence number of a signal in a queue.

This functionality is required for checkpointing pending signals.

Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Dave Jones <davej@redhat.com>
Cc: Andrey Vagin <avagin@openvz.org>
Cc: Michael Kerrisk <mtk.manpages@gmail.com>
Cc: Pavel Emelyanov <xemul@parallels.com>
CC: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Andrey Vagin <avagin@openvz.org>
---
fs/signalfd.c | 52 ++++++++++++++++++++++++++++++++++++++++---
include/uapi/linux/signalfd.h | 2 ++
2 files changed, 51 insertions(+), 3 deletions(-)

diff --git a/fs/signalfd.c b/fs/signalfd.c
index 8019ec9..a160a7c 100644
--- a/fs/signalfd.c
+++ b/fs/signalfd.c
@@ -51,6 +51,47 @@ struct signalfd_ctx {
sigset_t sigmask;
};

+static int peek_signal(struct sigpending *pending, sigset_t *mask,
+ siginfo_t *info, loff_t *pseq)
+{
+ struct sigqueue *q;
+ int ret = 0;
+
+ spin_lock_irq(&current->sighand->siglock);
+
+ list_for_each_entry(q, &pending->list, list) {
+ if (sigismember(mask, q->info.si_signo))
+ continue;
+
+ if ((*pseq)-- == 0) {
+ copy_siginfo(info, &q->info);
+ ret = info->si_signo;
+ break;
+ }
+ }
+
+ spin_unlock_irq(&current->sighand->siglock);
+
+ return ret;
+}
+
+static ssize_t signalfd_peek(struct signalfd_ctx *ctx,
+ siginfo_t *info, loff_t *ppos, int queue_mask)
+{
+ loff_t seq = *ppos;
+ int signr = 0;
+
+ if (queue_mask & SIGQUEUE_PRIVATE)
+ signr = peek_signal(&current->pending,
+ &ctx->sigmask, info, &seq);
+ if (!signr && (queue_mask & SIGQUEUE_SHARED))
+ signr = peek_signal(&current->signal->shared_pending,
+ &ctx->sigmask, info, &seq);
+ (*ppos)++;
+
+ return signr;
+}
+
static int signalfd_release(struct inode *inode, struct file *file)
{
kfree(file->private_data);
@@ -259,7 +300,10 @@ static ssize_t signalfd_read(struct file *file, char __user *buf, size_t count,

siginfo = (struct signalfd_siginfo __user *) buf;
do {
- ret = signalfd_dequeue(ctx, &info, nonblock, qmask);
+ if (file->f_flags & SFD_PEEK)
+ ret = signalfd_peek(ctx, &info, ppos, qmask);
+ else
+ ret = signalfd_dequeue(ctx, &info, nonblock, qmask);

if (unlikely(ret <= 0))
break;
@@ -315,7 +359,8 @@ SYSCALL_DEFINE4(signalfd4, int, ufd, sigset_t __user *, user_mask,
BUILD_BUG_ON(SFD_CLOEXEC != O_CLOEXEC);
BUILD_BUG_ON(SFD_NONBLOCK != O_NONBLOCK);

- if (flags & ~(SFD_CLOEXEC | SFD_NONBLOCK | SFD_RAW | SFD_QUEUES))
+ if (flags & ~(SFD_CLOEXEC | SFD_NONBLOCK |
+ SFD_RAW | SFD_PEEK | SFD_QUEUES))
return -EINVAL;

if (sizemask != sizeof(sigset_t) ||
@@ -352,7 +397,8 @@ SYSCALL_DEFINE4(signalfd4, int, ufd, sigset_t __user *, user_mask,
}

file->f_flags |= (flags & SFD_QUEUES) ? : SFD_QUEUES;
- file->f_flags |= flags & SFD_RAW;
+ file->f_flags |= flags & (SFD_RAW | SFD_PEEK);
+ file->f_mode |= FMODE_PREAD;

fd_install(ufd, file);
} else {
diff --git a/include/uapi/linux/signalfd.h b/include/uapi/linux/signalfd.h
index 481b658..24c5d2d 100644
--- a/include/uapi/linux/signalfd.h
+++ b/include/uapi/linux/signalfd.h
@@ -20,6 +20,8 @@
#define SFD_SHARED_QUEUE O_DIRECTORY
/* Read signals from a per-thread queue */
#define SFD_PER_THREAD_QUEUE O_EXCL
+/* Read signals without removing them from a queue */
+#define SFD_PEEK O_APPEND

struct signalfd_siginfo {
__u32 ssi_signo;
--
1.7.11.7


\
 
 \ /
  Last update: 2013-01-22 12:01    [W:0.155 / U:1.352 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site