Messages in this thread | | | From | Linus Torvalds <> | Date | Wed, 24 Jul 2019 10:37:34 -0700 | Subject | Re: [RFC][PATCH 1/5] exit: kill struct waitid_info |
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On Wed, Jul 24, 2019 at 7:47 AM Christian Brauner <christian@brauner.io> wrote: > > The code here uses a struct waitid_info to catch basic information about > process exit including the pid, uid, status, and signal that caused the > process to exit. This information is then stuffed into a struct siginfo > for the waitid() syscall. That seems like an odd thing to do. We can > just pass down a siginfo_t struct directly which let's us cleanup and > simplify the whole code quite a bit.
Ack. Except I'd like the commit message to explain where this comes from instead of that "That seems like an odd thing to do".
The _original_ reason for "struct waitid_info" was that "siginfo_t" is huge because of all the insane padding that various architectures do.
So it was introduced by commit 67d7ddded322 ("waitid(2): leave copyout of siginfo to syscall itself") very much to avoid stack usage issues. And I quote:
collect the information needed for siginfo into a small structure (waitid_info)
simply because "sigset_t" was big.
But that size came from the explicit "pad it out to 128 bytes for future expansion that will never happen", and the kernel using the same exact sigset_t that was exposed to user space.
Then in commit 4ce5f9c9e754 ("signal: Use a smaller struct siginfo in the kernel") we got rid of the insane padding for in-kernel use, exactly because it causes issues like this.
End result: that "struct waitid_info" no longer makes sense. It's not appreciably smaller than kernel_siginfo_t is today, but it made sense at the time.
Linus
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