2012/12/28 Oleg Nesterov <oleg@xxxxxxxxxx>:
> On 12/28, Andrey Vagin wrote:
>>
>> signalfd should be called with the flag SFD_RAW for that.
>>
>> signalfd_siginfo is not full for siginfo with a negative si_code.
>> copy_siginfo_to_user() is copied a full siginfo to user-space, if
>> si_code is negative. signalfd_copyinfo() doesn't do that and can't be
>> expanded, because it has not compatible format with siginfo_t.
>>
>> Another problem is that a constant __SI_* is removed from si_code.
>> It's not a problem for usual applications, because they expect
>> a defined type of siginfo (internal logic).
>> When we want to dump pending signals, we can't predict a type of
>> siginfo, so we should get it from kernel.
>>
>> The main idea of the raw format is that it should be enough for
>> restoring exactly the same siginfo for the current process.
>>
>> This functionality is required for checkpointing pending signals.
>
> And this should be used along with pread().
>
> I won't argue, but perhaps we should simply postulate that pread()
> always dumps siginfo in raw format and avoid the new flag?
I won't argue too:), but I think the flag is more flexiable. The flag
allows to get raw siginfo from read(), it may be useful not only for
checkpoint/restore. pread with offset = 0 is equal to read(), so the
interface with the flag is more clear.
>
>> @@ -272,20 +311,35 @@ SYSCALL_DEFINE4(signalfd4, int, ufd, sigset_t __user *, user_mask,
>> signotset(&sigmask);
>>
>> if (ufd == -1) {
>> + struct file *file;
>> ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
>> if (!ctx)
>> return -ENOMEM;
>>
>> ctx->sigmask = sigmask;
>>
>> + ufd = get_unused_fd_flags(flags);
>> + if (ufd < 0) {
>> + kfree(ctx);
>> + goto out;
>> + }
>> +
>> /*
>> * When we call this, the initialization must be complete, since
>> * anon_inode_getfd() will install the fd.
>> */
>> - ufd = anon_inode_getfd("[signalfd]", &signalfd_fops, ctx,
>> + file = anon_inode_getfile("[signalfd]", &signalfd_fops, ctx,
>> O_RDWR | (flags & (O_CLOEXEC | O_NONBLOCK)));
>> - if (ufd < 0)
>> + if (IS_ERR(file)) {
>> + put_unused_fd(ufd);
>> + ufd = PTR_ERR(file);
>> kfree(ctx);
>> + goto out;
>> + }
>> +
>> + file->f_flags |= flags & SFD_RAW;
>> +
>> + fd_install(ufd, file);
>
> And this is needed because we want to set more bits in f_flags/f_mode.
>
> I am wondering if we can change anon_inode_getfd/getfile somehow so
> that the user can pass more flags...
>
> Or. Currently fops->open() is never used if this file_operations is used
> by anon_inode_get*. So perhaps we can change anon_inode_getfile() to call
> fops->open() if it is not zero before return?
>
> OK, this is almost off-topic, please ignore.
>
> Oleg.
>
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