Hi On Tue, Jul 26, 2022 at 12:44 PM Daniel P. Berrangé <berrange@redhat.com> wrote:
On Tue, Jul 26, 2022 at 12:32:32PM +0400, marcandre.lureau@redhat.com wrote:
From: Marc-André Lureau <marcandre.lureau@redhat.com>
As Ed Swierk explained back in 2006: https://lists.nongnu.org/archive/html/qemu-devel/2006-12/msg00160.html
"When qemu writes into the pipe, it immediately reads back what it just wrote and treats it as a monitor command, endlessly breathing its own exhaust."
This is similarly confusing when using the chardev with a serial device, as reported in https://bugzilla.redhat.com/show_bug.cgi?id=2106975.
It seems we have kept the support for bidirectional pipes for historical reasons and odd systems, however it's not documented in qemu -chardev options. I suggest to stop supporting it, for portability reasons.
Hmm, I always assumed that in this scenario the pipe was operating in output-only mode. Obviously not the case with the code as it exists, but perhaps this would be useful ? eg its good as a serial console logging mechanism at least.
The current "-chardev pipe,id=id,path=path" option handling will first check the presence of unidirectional "path.in" & "path.out" (although they are opened RDWR...), and fallback on bidirectional "path". We could allow for the presence of "path.out" alone, although this may be a behaviour/breaking change: diff --git a/chardev/char-pipe.c b/chardev/char-pipe.c index 7db963035e..f78bcd7daf 100644 --- a/chardev/char-pipe.c +++ b/chardev/char-pipe.c @@ -137,12 +137,12 @@ static void qemu_chr_open_pipe(Chardev *chr, g_free(filename_in); g_free(filename_out); if (fd_in < 0 || fd_out < 0) { + if (fd_out >= 0) { + goto out; + } if (fd_in >= 0) { close(fd_in); } - if (fd_out >= 0) { - close(fd_out); - } warn_report("Support for bidirectional pipe is deprecated,"); warn_report("please use portable one-way pipes instead (%s.in & %s.out).", filename, filename); @@ -152,6 +152,7 @@ static void qemu_chr_open_pipe(Chardev *chr, return; } } +out: qemu_chr_open_fd(chr, fd_in, fd_out); or we introduce a new "access=write" option, or a new chardev type ?
Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com> --- docs/about/deprecated.rst | 6 ++++++ chardev/char-pipe.c | 4 ++++ 2 files changed, 10 insertions(+)
diff --git a/docs/about/deprecated.rst b/docs/about/deprecated.rst index 7ee26626d5cf..dd5ca30d527b 100644 --- a/docs/about/deprecated.rst +++ b/docs/about/deprecated.rst @@ -45,6 +45,12 @@ transmit audio through the VNC protocol. ``tty`` and ``parport`` are aliases that will be removed. Instead, the actual backend names ``serial`` and ``parallel`` should be used.
+``-chardev pipe`` support for bidirectional pipes (since 7.1) +'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' + +For portability reasons, the support for bidirectional ``pipe`` will +be removed. Instead, use ``file.in`` & ``file.out`` unidirectional pipes. + Short-form boolean options (since 6.0) ''''''''''''''''''''''''''''''''''''''
diff --git a/chardev/char-pipe.c b/chardev/char-pipe.c index 66d3b8509183..7db963035e7d 100644 --- a/chardev/char-pipe.c +++ b/chardev/char-pipe.c @@ -27,6 +27,7 @@ #include "qemu/main-loop.h" #include "qemu/module.h" #include "qemu/option.h" +#include "qemu/error-report.h" #include "chardev/char.h"
#ifdef _WIN32 @@ -142,6 +143,9 @@ static void qemu_chr_open_pipe(Chardev *chr, if (fd_out >= 0) { close(fd_out); } + warn_report("Support for bidirectional pipe is deprecated,"); + warn_report("please use portable one-way pipes instead (%s.in & %s.out).", + filename, filename); TFR(fd_in = fd_out = qemu_open_old(filename, O_RDWR | O_BINARY)); if (fd_in < 0) { error_setg_file_open(errp, errno, filename); -- 2.37.0.rc0
With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|