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From 0bb331d124049a9157c08bb1d3572493e6691f05 Mon Sep 17 00:00:00 2001
From: Amit Shah <amit.shah@redhat.com>
Date: Mon, 21 Mar 2011 22:00:27 +0100
Subject: [PATCH] char: Update send_all() to handle nonblocking chardev write
 requests

The send_all function is modified to return to the caller in case the
driver cannot handle any more data.  It returns -EAGAIN or
WSAEWOULDBLOCK on non-Windows and Windows platforms respectively.  This
is only done when the caller sets a callback function handler indicating
it's not interested in blocking till the driver has written out all the
data.

Currently there's no driver or caller that supports this.  Future
commits will add such capability.

Signed-off-by: Amit Shah <amit.shah@redhat.com>
Signed-off-by: Cole Robinson <crobinso@redhat.com>
---
 qemu-char.c   | 69 +++++++++++++++++++++++++++++++++++++++++++++++++++++------
 qemu_socket.h |  2 +-
 2 files changed, 64 insertions(+), 7 deletions(-)

diff --git a/qemu-char.c b/qemu-char.c
index b5266d1..b46cc97 100644
--- a/qemu-char.c
+++ b/qemu-char.c
@@ -508,7 +508,7 @@ static CharDriverState *qemu_chr_open_mux(CharDriverState *drv)
 
 
 #ifdef _WIN32
-int send_all(int fd, const void *buf, int len1)
+static int do_send(int fd, const void *buf, int len1, bool nonblock)
 {
     int ret, len;
 
@@ -516,9 +516,14 @@ int send_all(int fd, const void *buf, int len1)
     while (len > 0) {
         ret = send(fd, buf, len, 0);
         if (ret < 0) {
+            if (nonblock && len1 - len) {
+                return len1 - len;
+            }
             errno = WSAGetLastError();
             if (errno != WSAEWOULDBLOCK) {
                 return -1;
+            } else if (errno == WSAEWOULDBLOCK && nonblock) {
+                return WSAEWOULDBLOCK;
             }
         } else if (ret == 0) {
             break;
@@ -532,7 +537,7 @@ int send_all(int fd, const void *buf, int len1)
 
 #else
 
-int send_all(int fd, const void *_buf, int len1)
+static int do_send(int fd, const void *_buf, int len1, bool nonblock)
 {
     int ret, len;
     const uint8_t *buf = _buf;
@@ -541,8 +546,15 @@ int send_all(int fd, const void *_buf, int len1)
     while (len > 0) {
         ret = write(fd, buf, len);
         if (ret < 0) {
-            if (errno != EINTR && errno != EAGAIN)
+            if (nonblock && len1 - len) {
+                return len1 - len;
+            }
+            if (errno == EAGAIN && nonblock) {
+                return -EAGAIN;
+            }
+            if (errno != EINTR && errno != EAGAIN) {
                 return -1;
+            }
         } else if (ret == 0) {
             break;
         } else {
@@ -557,6 +569,44 @@ int send_all(int fd, const void *_buf, int len1)
 #define STDIO_MAX_CLIENTS 1
 static int stdio_nb_clients;
 
+int send_all(CharDriverState *chr, int fd, const void *_buf, int len1)
+{
+    int ret, eagain_errno;
+    bool nonblock;
+
+    if (chr && chr->write_blocked) {
+        /*
+         * The caller should not send us data while we're blocked,
+         * but this can happen when multiple writers are woken at once,
+         * so simply return -EAGAIN.
+         */
+        return -EAGAIN;
+    }
+
+    nonblock = false;
+    /*
+     * Ensure the char backend is able to receive and handle the
+     * 'write unblocked' event before we turn on nonblock support.
+     */
+    if (chr && chr->chr_enable_write_fd_handler && chr->chr_write_unblocked) {
+        nonblock = true;
+    }
+    ret = do_send(fd, _buf, len1, nonblock);
+
+#ifdef _WIN32
+    eagain_errno = WSAEWOULDBLOCK;
+#else
+    eagain_errno = -EAGAIN;
+#endif
+
+    if (nonblock && (ret == eagain_errno || (ret >= 0 && ret < len1))) {
+        /* Update fd handler to wake up when chr becomes writable */
+        chr->chr_enable_write_fd_handler(chr);
+        chr->write_blocked = true;
+    }
+    return ret;
+}
+
 #ifndef _WIN32
 
 typedef struct {
@@ -568,7 +618,7 @@ typedef struct {
 static int fd_chr_write(CharDriverState *chr, const uint8_t *buf, int len)
 {
     FDCharDriver *s = chr->opaque;
-    return send_all(s->fd_out, buf, len);
+    return send_all(chr, s->fd_out, buf, len);
 }
 
 static int fd_chr_read_poll(void *opaque)
@@ -887,7 +937,7 @@ static int pty_chr_write(CharDriverState *chr, const uint8_t *buf, int len)
         pty_chr_update_read_handler(chr);
         return 0;
     }
-    return send_all(s->fd, buf, len);
+    return send_all(chr, s->fd, buf, len);
 }
 
 static int pty_chr_read_poll(void *opaque)
@@ -2174,8 +2224,15 @@ static void tcp_closed(void *opaque)
 static int tcp_chr_write(CharDriverState *chr, const uint8_t *buf, int len)
 {
     TCPCharDriver *s = chr->opaque;
+
     if (s->connected) {
-        return send_all(s->fd, buf, len);
+        int ret;
+
+        ret = send_all(chr, s->fd, buf, len);
+        if (ret == -1 && errno == EPIPE) {
+            tcp_closed(chr);
+        }
+        return ret;
     } else {
         /* XXX: indicate an error ? */
         return len;
diff --git a/qemu_socket.h b/qemu_socket.h
index 3e8aee9..a537d86 100644
--- a/qemu_socket.h
+++ b/qemu_socket.h
@@ -36,7 +36,7 @@ int qemu_accept(int s, struct sockaddr *addr, socklen_t *addrlen);
 int socket_set_cork(int fd, int v);
 void socket_set_block(int fd);
 void socket_set_nonblock(int fd);
-int send_all(int fd, const void *buf, int len1);
+int send_all(CharDriverState *chr, int fd, const void *buf, int len1);
 
 /* callback function for nonblocking connect
  * valid fd on success, negative error code on failure