[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <gnj4drf7llod4voaaasoh5jdlq545gduishrbc3ql3665pw7qy@ytd5ykxc4gsr>
Date: Mon, 10 Jul 2023 00:33:06 +0200
From: Ahelenia Ziemiańska
<nabijaczleweli@...ijaczleweli.xyz>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Christian Brauner <brauner@...nel.org>,
Jens Axboe <axboe@...nel.dk>,
David Howells <dhowells@...hat.com>,
Alexander Viro <viro@...iv.linux.org.uk>,
linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: Pending splice(file -> FIFO) excludes all other FIFO operations
forever (was: ... always blocks read(FIFO), regardless of O_NONBLOCK on read
side?)
On Sun, Jul 09, 2023 at 03:03:22AM +0200, Ahelenia Ziemiańska wrote:
> On Sat, Jul 08, 2023 at 01:06:56PM -0700, Linus Torvalds wrote:
> > I guess combined with something like
> >
> > if (!(in->f_mode & FMODE_NOWAIT))
> > return -EINVAL;
> >
> > it might all work.
> Yes, that makes the splice instantly -EINVAL for ttys, but doesn't
> affect the socketpair() case above, which still blocks forever.
This also triggers for regular file -> pipe splices,
which is probably a no-go.
Attaching a summary diff that does all I said in the previous mail.
filemap_get_pages() does use and inspect IOCB_NOWAIT if set in
filemap_splice_read(), but it appears to not really make much sense,
inasmuch it returns EAGAIN for the first splice() from a
blockdev and then instantly return with data on the next go-around.
This doesn't really make much sense ‒ and open(2) says blockdevs
don't have O_NONBLOCK semantics, so I'm assuming this is not supposed
to be exposed to userspace ‒ so I'm not setting it in the diff.
I've tested this for:
* tty: -EINVAL
* socketpair(AF_UNIX, SOCK_STREAM): works as expected
$ wc -c fifo &
[1] 261
$ ./af_unix ./s > fifo
5 Success
6454 Resource temporarily unavailable
5 Success
6445 Resource temporarily unavailable
0 Success
10 fifo
* socket(AF_INET, SOCK_STREAM, 0): works as expected
$ wc fifo &
[1] 249
$ ./tcp ./s > fifo
23099 Resource temporarily unavailable
7 Success
2099 Resource temporarily unavailable
4 Success
1751 Resource temporarily unavailable
3 Success
21655 Resource temporarily unavailable
95 Success
19589 Resource temporarily unavailable
0 Success
4 15 109 fifo
corresponding to
host$ nc 127.0.0.1 14640
żupan
asd
ad
asdda dasj aiojd askdl; jasiopdij as[pkdo[p askd9p ias90dk aso[pjd 890pasid90[ jaskl;dj il;asd
^C
* blockdev (/dev/vda): as expected (with filemap_splice_read() unchanged), copies it all
* regular file: -EINVAL(!)
Splicers still sleep if the pipe's full, of course,
unless SPLICE_F_NONBLOCK.
Test drivers attached as well.
View attachment "nowait.diff" of type "text/x-diff" (7196 bytes)
View attachment "s.c" of type "text/x-csrc" (485 bytes)
View attachment "tcp.c" of type "text/x-csrc" (507 bytes)
View attachment "af_unix.c" of type "text/x-csrc" (394 bytes)
Download attachment "signature.asc" of type "application/pgp-signature" (834 bytes)
Powered by blists - more mailing lists