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From: Stefan Metzmacher <[email protected]>
To: Pavel Begunkov <[email protected]>,
	Jens Axboe <[email protected]>,
	[email protected]
Cc: "[email protected]" <[email protected]>
Subject: Re: [PATCH 0/2] send[msg]()/recv[msg]() fixes/improvements
Date: Thu, 18 Mar 2021 01:15:30 +0100	[thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>

Hi Pavel,

>>>>> here're patches which fix linking of send[msg]()/recv[msg]() calls
>>>>> and make sure io_uring_enter() never generate a SIGPIPE.
>>>
>>> 1/2 breaks userspace.
>>
>> Can you explain that a bit please, how could some application ever
>> have a useful use of IOSQE_IO_LINK with these socket calls?
> 
> Packet delivery of variable size, i.e. recv(max_size). Byte stream
> that consumes whatever you've got and links something (e.g. notification
> delivery, or poll). Not sure about netlink, but maybe. Or some
> "create a file via send" crap, or some made-up custom protocols

Ok, then we need a flag or a new opcode to provide that behavior?

For recv() and recvmsg() MSG_WAITALL might be usable.

It's not defined in 'man 2 sendmsg', but should we use it anyway
for IORING_OP_SEND[MSG] in order to activate the short send check
as the low level sock_sendmsg() call seem to ignore unused flags,
which seems to be the reason for the following logic in tcp_sendmsg_locked:

if (flags & MSG_ZEROCOPY && size && sock_flag(sk, SOCK_ZEROCOPY)) {

You need to set SOCK_ZEROCOPY in the socket in order to give a meaning
to MSG_ZEROCOPY.

Should I prepare an add-on patch to make the short send/recv logic depend
on MSG_WAITALL?

I'm cc'ing [email protected] in order to more feedback of
MSG_WAITALL can be passed to sendmsg without fear to trigger
-EINVAL.

The example for io_sendmsg() would look like this:

--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -4383,7 +4383,7 @@ static int io_sendmsg(struct io_kiocb *req, unsigned int issue_flags)
        struct io_async_msghdr iomsg, *kmsg;
        struct socket *sock;
        unsigned flags;
-       int expected_ret;
+       int min_ret = 0;
        int ret;

        sock = sock_from_file(req->file);
@@ -4404,9 +4404,11 @@ static int io_sendmsg(struct io_kiocb *req, unsigned int issue_flags)
        else if (issue_flags & IO_URING_F_NONBLOCK)
                flags |= MSG_DONTWAIT;

-       expected_ret = iov_iter_count(&kmsg->msg.msg_iter);
-       if (unlikely(expected_ret == MAX_RW_COUNT))
-               expected_ret += 1;
+       if (flags & MSG_WAITALL) {
+               min_ret = iov_iter_count(&kmsg->msg.msg_iter);
+               if (unlikely(min_ret == MAX_RW_COUNT))
+                       min_ret += 1;
+       }
        ret = __sys_sendmsg_sock(sock, &kmsg->msg, flags);
        if ((issue_flags & IO_URING_F_NONBLOCK) && ret == -EAGAIN)
                return io_setup_async_msg(req, kmsg);
@@ -4417,7 +4419,7 @@ static int io_sendmsg(struct io_kiocb *req, unsigned int issue_flags)
        if (kmsg->free_iov)
                kfree(kmsg->free_iov);
        req->flags &= ~REQ_F_NEED_CLEANUP;
-       if (ret != expected_ret)
+       if (ret < min_ret)
                req_set_fail_links(req);
        __io_req_complete(req, issue_flags, ret, 0);
        return 0;

Which means the default of min_ret = 0 would result in:

        if (ret < 0)
                req_set_fail_links(req);

again...

>>> Sounds like 2/2 might too, does it?
>>
>> Do you think any application really expects to get a SIGPIPE
>> when calling io_uring_enter()?
> 
> If it was about what I think I would remove lots of old garbage :)
> I doubt it wasn't working well before, e.g. because of iowq, but
> who knows

Yes, it was inconsistent before and now it's reliable.

metze




  reply	other threads:[~2021-03-18  0:16 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-16 15:33 [PATCH 0/2] send[msg]()/recv[msg]() fixes/improvements Stefan Metzmacher
2021-03-16 15:33 ` [PATCH 1/2] io_uring: call req_set_fail_links() on short send[msg]()/recv[msg]() calls Stefan Metzmacher
2021-03-20 19:33   ` [PATCH v2 1/1] io_uring: call req_set_fail_links() on short send[msg]()/recv[msg]() with MSG_WAITALL Stefan Metzmacher
2021-03-20 22:57     ` Jens Axboe
2021-03-21 10:20       ` Stefan Metzmacher
2021-03-21 13:10         ` Jens Axboe
2021-03-16 15:33 ` [PATCH 2/2] io_uring: imply MSG_NOSIGNAL for send[msg]()/recv[msg]() calls Stefan Metzmacher
2021-03-17 22:36 ` [PATCH 0/2] send[msg]()/recv[msg]() fixes/improvements Jens Axboe
2021-03-17 23:07   ` Pavel Begunkov
2021-03-17 23:24     ` Jens Axboe
2021-03-17 23:26     ` Stefan Metzmacher
2021-03-17 23:39       ` Pavel Begunkov
2021-03-18  0:15         ` Stefan Metzmacher [this message]
2021-03-18 13:00           ` Pavel Begunkov
2021-03-18 13:08           ` Pavel Begunkov

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