[Qemu-devel] [4956] Attempt to detect unconnected ptys (Gerd Hoffman)

[Anthony Liguori <anthony@codemonkey.ws>]

Revision: 4956
          http://svn.sv.gnu.org/viewvc/?view=rev&root=qemu&revision=4956
Author:   aliguori
Date:     2008-07-28 18:55:32 +0000 (Mon, 28 Jul 2008)

Log Message:
-----------
Attempt to detect unconnected ptys (Gerd Hoffman)

This patch moves the pty char device imlementation away from the generic
filehandle code.  It tries to detect as good as possible whenever there
is someone connected to the slave pty device and only send data down the
road in case someone is listening.  Unfortunaly we have to poll via
timer once in a while to check the status because we have to use read()
on the master pty to figure the status (returns -EIO when unconnected).

Poll intervall for an idle guest is one second, when the guest sends
data to the virtual device linked to the pty we check more frequently.

The point for all of this is to avoid qemu blocking and not responding
any more.  Writing to the master pty handle succeeds even when nobody is
connected to (and reading from) to the slave end of the pty.  The kernel
just bufferes the writes.  And as soon as the kernel buffer is full the
write() call blocks forever ...

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

Modified Paths:
--------------
    trunk/vl.c

Modified: trunk/vl.c
===================================================================
--- trunk/vl.c	2008-07-27 11:09:21 UTC (rev 4955)
+++ trunk/vl.c	2008-07-28 18:55:32 UTC (rev 4956)
@@ -2464,21 +2464,162 @@
 #endif
 
 #if defined(__linux__) || defined(__sun__)
+
+typedef struct {
+    int fd;
+    int connected;
+    int polling;
+    int read_bytes;
+    QEMUTimer *timer;
+} PtyCharDriver;
+
+static void pty_chr_update_read_handler(CharDriverState *chr);
+static void pty_chr_state(CharDriverState *chr, int connected);
+
+static int pty_chr_write(CharDriverState *chr, const uint8_t *buf, int len)
+{
+    PtyCharDriver *s = chr->opaque;
+
+    if (!s->connected) {
+        /* guest sends data, check for (re-)connect */
+        pty_chr_update_read_handler(chr);
+        return 0;
+    }
+    return unix_write(s->fd, buf, len);
+}
+
+static int pty_chr_read_poll(void *opaque)
+{
+    CharDriverState *chr = opaque;
+    PtyCharDriver *s = chr->opaque;
+
+    s->read_bytes = qemu_chr_can_read(chr);
+    return s->read_bytes;
+}
+
+static void pty_chr_read(void *opaque)
+{
+    CharDriverState *chr = opaque;
+    PtyCharDriver *s = chr->opaque;
+    int size, len;
+    uint8_t buf[1024];
+
+    len = sizeof(buf);
+    if (len > s->read_bytes)
+        len = s->read_bytes;
+    if (len == 0)
+        return;
+    size = read(s->fd, buf, len);
+    if ((size == -1 && errno == EIO) ||
+        (size == 0)) {
+        pty_chr_state(chr, 0);
+        return;
+    }
+    if (size > 0) {
+        pty_chr_state(chr, 1);
+        qemu_chr_read(chr, buf, size);
+    }
+}
+
+static void pty_chr_update_read_handler(CharDriverState *chr)
+{
+    PtyCharDriver *s = chr->opaque;
+
+    qemu_set_fd_handler2(s->fd, pty_chr_read_poll,
+                         pty_chr_read, NULL, chr);
+    s->polling = 1;
+    /*
+     * Short timeout here: just need wait long enougth that qemu makes
+     * it through the poll loop once.  When reconnected we want a
+     * short timeout so we notice it almost instantly.  Otherwise
+     * read() gives us -EIO instantly, making pty_chr_state() reset the
+     * timeout to the normal (much longer) poll interval before the
+     * timer triggers.
+     */
+    qemu_mod_timer(s->timer, qemu_get_clock(rt_clock) + 10);
+}
+
+static void pty_chr_state(CharDriverState *chr, int connected)
+{
+    PtyCharDriver *s = chr->opaque;
+
+    if (!connected) {
+        qemu_set_fd_handler2(s->fd, NULL, NULL, NULL, NULL);
+        s->connected = 0;
+        s->polling = 0;
+        /* (re-)connect poll interval for idle guests: once per second.
+         * We check more frequently in case the guests sends data to
+         * the virtual device linked to our pty. */
+        qemu_mod_timer(s->timer, qemu_get_clock(rt_clock) + 1000);
+    } else {
+        if (!s->connected)
+            qemu_chr_reset(chr);
+        s->connected = 1;
+    }
+}
+
+void pty_chr_timer(void *opaque)
+{
+    struct CharDriverState *chr = opaque;
+    PtyCharDriver *s = chr->opaque;
+
+    if (s->connected)
+        return;
+    if (s->polling) {
+        /* If we arrive here without polling being cleared due
+         * read returning -EIO, then we are (re-)connected */
+        pty_chr_state(chr, 1);
+        return;
+    }
+
+    /* Next poll ... */
+    pty_chr_update_read_handler(chr);
+}
+
+static void pty_chr_close(struct CharDriverState *chr)
+{
+    PtyCharDriver *s = chr->opaque;
+
+    qemu_set_fd_handler2(s->fd, NULL, NULL, NULL, NULL);
+    close(s->fd);
+    qemu_free(s);
+}
+
 static CharDriverState *qemu_chr_open_pty(void)
 {
+    CharDriverState *chr;
+    PtyCharDriver *s;
     struct termios tty;
-    int master_fd, slave_fd;
+    int slave_fd;
 
-    if (openpty(&master_fd, &slave_fd, NULL, NULL, NULL) < 0) {
+    chr = qemu_mallocz(sizeof(CharDriverState));
+    if (!chr)
         return NULL;
+    s = qemu_mallocz(sizeof(PtyCharDriver));
+    if (!s) {
+        qemu_free(chr);
+        return NULL;
     }
 
+    if (openpty(&s->fd, &slave_fd, NULL, NULL, NULL) < 0) {
+        return NULL;
+    }
+
     /* Set raw attributes on the pty. */
     cfmakeraw(&tty);
     tcsetattr(slave_fd, TCSAFLUSH, &tty);
+    close(slave_fd);
 
-    fprintf(stderr, "char device redirected to %s\n", ptsname(master_fd));
-    return qemu_chr_open_fd(master_fd, master_fd);
+    fprintf(stderr, "char device redirected to %s\n", ptsname(s->fd));
+
+    chr->opaque = s;
+    chr->chr_write = pty_chr_write;
+    chr->chr_update_read_handler = pty_chr_update_read_handler;
+    chr->chr_close = pty_chr_close;
+
+    s->timer = qemu_new_timer(rt_clock, pty_chr_timer, chr);
+
+    return chr;
 }
 
 static void tty_serial_init(int fd, int speed,