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[Qemu-devel] [PULL 03/28] qemu-char: Keep pty slave file descriptor open

From: Paolo Bonzini
Subject: [Qemu-devel] [PULL 03/28] qemu-char: Keep pty slave file descriptor open until the master is closed
Date: Mon, 8 Feb 2016 18:02:54 +0100

If a process opens the slave pts device, writes data to it, then
immediately closes it, the data doesn't reliably get delivered to the
emulated serial port. This seems to be because a read of the master
pty device returns EIO on Linux if no process has the pts device open,
even when data is waiting "in the pipe".

A fix seems to be for QEMU to keep the pts file descriptor open until
the pty is closed, as per the below patch.

Signed-off-by: Ashley Jonathan <address@hidden>
Message-Id: <address@hidden>
Reviewed-by: Michael Tokarev <address@hidden>
Signed-off-by: Paolo Bonzini <address@hidden>
 qemu-char.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/qemu-char.c b/qemu-char.c
index 927c47e..1fbccf0 100644
--- a/qemu-char.c
+++ b/qemu-char.c
@@ -1171,6 +1171,7 @@ typedef struct {
     int connected;
     guint timer_tag;
     guint open_tag;
+    int slave_fd;
 } PtyCharDriver;
 static void pty_chr_update_read_handler_locked(CharDriverState *chr);
@@ -1347,6 +1348,7 @@ static void pty_chr_close(struct CharDriverState *chr)
     pty_chr_state(chr, 0);
+    close(s->slave_fd);
     if (s->timer_tag) {
@@ -1374,7 +1376,6 @@ static CharDriverState *qemu_chr_open_pty(const char *id,
         return NULL;
-    close(slave_fd);
     chr = qemu_chr_alloc(common, errp);
@@ -1399,6 +1400,7 @@ static CharDriverState *qemu_chr_open_pty(const char *id,
     chr->explicit_be_open = true;
     s->ioc = QIO_CHANNEL(qio_channel_file_new_fd(master_fd));
+    s->slave_fd = slave_fd;
     s->timer_tag = 0;
     return chr;

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