Re: [PATCH 3/3] signalfd: add ability to read siginfo-s withoutdequeuing signals (v2)

From: Andrey Wagin
Date: Sat Feb 02 2013 - 02:16:28 EST


2013/2/2 Michael Kerrisk (man-pages) <mtk.manpages@xxxxxxxxx>:
>
> On Jan 30, 2013 8:05 AM, "Andrey Vagin" <avagin@xxxxxxxxxx> wrote:
>>
>> 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 / sizeof(signalfd_siginfo) is a sequence number of a signal
>> in a queue.
>
> Andrey,
>
> Is it perhaps worth erroring (EINVAL) if ((ppos % sizeof
> (signalfd_siginfo)) != 0) ?

Yes, it's already in the patch.

@@ -257,9 +298,15 @@ static ssize_t signalfd_read(struct file *file,
char __user *buf, size_t count,
if (!count)
return -EINVAL;

+ if (*ppos % sizeof(struct signalfd_siginfo))
+ return -EINVAL;
+


>
> Cheers,
>
> Michael
>
>> This functionality is required for checkpointing pending signals.
>>
>> v2: * signals can be dumped only from one queue.
>> * treat pos as offset in bytes, not in elements, so pos should be
>> aligned to the size of signalfd_siginfo.
>>
>> Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
>> Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
>> Cc: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>
>> Cc: David Howells <dhowells@xxxxxxxxxx>
>> Cc: Dave Jones <davej@xxxxxxxxxx>
>> Cc: Andrey Vagin <avagin@xxxxxxxxxx>
>> Cc: Michael Kerrisk <mtk.manpages@xxxxxxxxx>
>> Cc: Pavel Emelyanov <xemul@xxxxxxxxxxxxx>
>> CC: Cyrill Gorcunov <gorcunov@xxxxxxxxxx>
>> Signed-off-by: Andrey Vagin <avagin@xxxxxxxxxx>
>> ---
>> fs/signalfd.c | 61
>> ++++++++++++++++++++++++++++++++++++++++---
>> include/uapi/linux/signalfd.h | 2 ++
>> 2 files changed, 60 insertions(+), 3 deletions(-)
>>
>> diff --git a/fs/signalfd.c b/fs/signalfd.c
>> index 8019ec9..0da6a30 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 / sizeof(struct signalfd_siginfo);
>> + int signr = 0;
>> +
>> + if (queue_mask & SIGQUEUE_PRIVATE)
>> + signr = peek_signal(&current->pending,
>> + &ctx->sigmask, info, &seq);
>> + else if (queue_mask & SIGQUEUE_SHARED)
>> + signr = peek_signal(&current->signal->shared_pending,
>> + &ctx->sigmask, info, &seq);
>> + (*ppos) += sizeof(struct signalfd_siginfo);
>> +
>> + return signr;
>> +}
>> +
>> static int signalfd_release(struct inode *inode, struct file *file)
>> {
>> kfree(file->private_data);
>> @@ -257,9 +298,15 @@ static ssize_t signalfd_read(struct file *file, char
>> __user *buf, size_t count,
>> if (!count)
>> return -EINVAL;
>>
>> + if (*ppos % sizeof(struct signalfd_siginfo))
>> + return -EINVAL;
>> +
>> 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 +362,12 @@ 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;
>> +
>> + /* SFD_PEEK can be used for one queue only */
>> + if ((flags & SFD_PEEK) && ((flags & SFD_QUEUES) == SFD_QUEUES))
>> return -EINVAL;
>>
>> if (sizemask != sizeof(sigset_t) ||
>> @@ -352,7 +404,10 @@ 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);
>> +
>> + if (file->f_flags & 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
>>
--
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