Date: Fri, 27 Jul 2012 21:08:13 +1000 (EST) From: Bruce Evans <brde@optusnet.com.au> To: davidxu@FreeBSD.org Cc: Garrett Cooper <yanegomi@gmail.com>, freebsd-bugs@FreeBSD.org, freebsd-gnats-submit@FreeBSD.org, Bruce Evans <brde@optusnet.com.au> Subject: Re: kern/170203: [kern] piped dd's don't behave sanely when dealing with a fifo Message-ID: <20120727210330.L6869@besplex.bde.org> In-Reply-To: <501256C6.5000307@gmail.com> References: <201207262256.q6QMurVf077480@red.freebsd.org> <20120727103622.B933@besplex.bde.org> <501256C6.5000307@gmail.com>
next in thread | previous in thread | raw e-mail | index | archive | help
On Fri, 27 Jul 2012, David Xu wrote: > On 2012/7/27 10:07, Bruce Evans wrote: >> >> I think it's working almost as expected. Large blocks give non-atomic >> I/O, so the reader sees small blocks, then EOF when it gets ahead of >> the writer. This always happens without SMP. >> >> Not is a bug (debugged below). There is no SIGPIPE at the start of >> write() because there is a reader then, and no SIGPIPE for the next >> write() because there is no next write() -- the current one doesn't >> notice when the reader goes away. >> > After fixed dd to not open fifo output file in O_RDWR mode, I still found the > writer is blocked there even the reader is already exited. I'm not sure that dd's open is a bug. It must be intentional to use O_RDWR for some cases. POSIX (old 2001 draft) doesn't say anything about dd's open mode. > I think this is definitely a bug. if reader is exited, the writer should be > aborted too, > but I found it still be blocked in state "pipedwt", obviously, the code in > /sys/fs/fifo_vnops.c wants to wake up the writer when the reader is closing > the fifo, > but it failed, because the bit flag PIPE_WANTW is forgotten to be set by > writer, > so it skips executing wakeup(), and then the writer has no chance to find EOF > bit flag > is set. Does this affect nameless pipes too? The old implementation presumably doesn't have this bug. Bruce
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20120727210330.L6869>