Messages in this thread | | | Subject | Re: [PATCH] af_unix: Allow Unix sockets to raise SIGURG | From | Shoaib Rao <> | Date | Fri, 29 Jan 2021 12:44:44 -0800 |
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On 1/29/21 12:18 PM, Jakub Kicinski wrote: > On Fri, 29 Jan 2021 12:10:21 -0800 Shoaib Rao wrote: >> On 1/29/21 12:02 PM, Jakub Kicinski wrote: >>> On Fri, 29 Jan 2021 11:48:15 -0800 Shoaib Rao wrote: >>>> Data was discarded because the flag was not supported, this patch >>>> changes that but does not support any urgent data. >>> When you say it does not support any urgent data do you mean the >>> message len must be == 0 because something is checking it, or that >>> the code does not support its handling? >>> >>> I'm perfectly fine with the former, just point me at the check, please. >> The code does not care about the size of data -- All it does is that if >> MSG_OOB is set it will deliver the signal to the peer process >> irrespective of the length of the data (which can be zero length). Let's >> look at the code of unix_stream_sendmsg() It does the following (sent is >> initialized to zero) > Okay. Let me try again. AFAICS your code makes it so that data sent > with MSG_OOB is treated like any other data. It just sends a signal. Correct. > So you're hijacking the MSG_OOB to send a signal, because OOB also > sends a signal. Correct. > But there is nothing OOB about the data itself. Correct. > So > I'm asking you to make sure that there is no data in the message. Yes I can do that. > That way when someone wants _actual_ OOB data on UNIX sockets they > can implement it without breaking backwards compatibility of the > kernel uAPI.
I see what you are trying to achieve. However it may not work.
Let's assume that __actual__ OOB data has been implemented. An application sends a zero length message with MSG_OOB, after that it sends some data (not suppose to be OOB data). How is the receiver going to differentiate if the data an OOB or not.
We could use a different flag (MSG_SIGURG) or implement the _actual_ OOB data semantics (If anyone is interested in it). MSG_SIGURG could be a generic flag that just sends SIGURG irrespective of the length of the data.
Shoaib
> >> while (sent < len) { >> size = len - sent; >> <..> >> >> } >> >> if (msg->msg_flags & MSG_OOB) >> sk_send_sigurg(other); >> >> Before the patch there was a check above the while loop that checked the >> flag and returned and error, that has been removed.
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