Patchwork [v5,4/6] char: Add qemu_chr_write_nb() for nonblocking writes

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Submitter Amit Shah
Date May 4, 2010, 10:52 a.m.
Message ID <1272970367-24647-5-git-send-email-amit.shah@redhat.com>
Download mbox | patch
Permalink /patch/51587/
State New
Headers show

Comments

Amit Shah - May 4, 2010, 10:52 a.m.
For char devices whose backing files are open in non-blocking mode,
non-blocking writes can now be made using qemu_chr_write_nb().

For non-blocking chardevs, we can return -EAGAIN to callers of
qemu_chr_write_nb(). When the backend is ready to accept more data,
we can let the caller know via a callback.

-EAGAIN is returned only when the backend's file is non-blocking
and a callback is registered by the caller when invoking
qemu_chr_add_handlers().

In case a backend doesn't support non-blocking writes,
qemu_chr_write_nb() invokes qemu_chr_write().

Individual callers can update their code to add a callback handler,
call qemu_chr_write_nb() instead of qemu_chr_write() if they wish to
receive -EAGAIN notifications.

No backend currently supports non-blocking writes.

Signed-off-by: Amit Shah <amit.shah@redhat.com>
---
 net/socket.c  |    4 ++--
 qemu-char.c   |   31 ++++++++++++++++++++++++-------
 qemu-char.h   |    8 ++++++++
 qemu_socket.h |    3 ++-
 4 files changed, 36 insertions(+), 10 deletions(-)

Patch

diff --git a/net/socket.c b/net/socket.c
index 1c4e153..8a401e6 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -56,8 +56,8 @@  static ssize_t net_socket_receive(VLANClientState *nc, const uint8_t *buf, size_
     uint32_t len;
     len = htonl(size);
 
-    send_all(s->fd, (const uint8_t *)&len, sizeof(len));
-    return send_all(s->fd, buf, size);
+    send_all(s->fd, (const uint8_t *)&len, sizeof(len), false);
+    return send_all(s->fd, buf, size, false);
 }
 
 static ssize_t net_socket_receive_dgram(VLANClientState *nc, const uint8_t *buf, size_t size)
diff --git a/qemu-char.c b/qemu-char.c
index 97f2ef6..d383c8f 100644
--- a/qemu-char.c
+++ b/qemu-char.c
@@ -145,6 +145,16 @@  int qemu_chr_write(CharDriverState *s, const uint8_t *buf, int len)
     return s->chr_write(s, buf, len);
 }
 
+ssize_t qemu_chr_write_nb(CharDriverState *s, const uint8_t *buf, size_t len)
+{
+    if (!s->nonblock) {
+        /* Fallback to blocking write if no callback registered */
+        return qemu_chr_write(s, buf, len);
+    }
+
+    return s->chr_write_nb(s, buf, len);
+}
+
 int qemu_chr_ioctl(CharDriverState *s, int cmd, void *arg)
 {
     if (!s->chr_ioctl)
@@ -203,11 +213,15 @@  void qemu_chr_add_handlers(CharDriverState *s,
     }
     s->chr_can_read = handlers->fd_can_read;
     s->chr_read = handlers->fd_read;
+    s->chr_write_unblocked = handlers->fd_write_unblocked;
     s->chr_event = handlers->fd_event;
     s->handler_opaque = opaque;
     if (s->chr_update_read_handler)
         s->chr_update_read_handler(s);
 
+    /* We'll set this at connect-time */
+    s->nonblock = false;
+
     /* We're connecting to an already opened device, so let's make sure we
        also get the open event */
     if (s->opened) {
@@ -499,7 +513,7 @@  static CharDriverState *qemu_chr_open_mux(CharDriverState *drv)
 
 
 #ifdef _WIN32
-int send_all(int fd, const void *buf, int len1)
+int send_all(int fd, const void *buf, int len1, bool nonblock)
 {
     int ret, len;
 
@@ -526,7 +540,7 @@  int send_all(int fd, const void *buf, int len1)
 
 #else
 
-static int unix_write(int fd, const uint8_t *buf, int len1)
+static int unix_write(int fd, const uint8_t *buf, int len1, bool nonblock)
 {
     int ret, len;
 
@@ -537,6 +551,9 @@  static int unix_write(int fd, const uint8_t *buf, int len1)
             if (len1 - len) {
                 return len1 - len;
             }
+            if (errno == EAGAIN && nonblock) {
+                return -EAGAIN;
+            }
             if (errno != EINTR && errno != EAGAIN) {
                 return -1;
             }
@@ -550,9 +567,9 @@  static int unix_write(int fd, const uint8_t *buf, int len1)
     return len1 - len;
 }
 
-int send_all(int fd, const void *buf, int len1)
+int send_all(int fd, const void *buf, int len1, bool nonblock)
 {
-    return unix_write(fd, buf, len1);
+    return unix_write(fd, buf, len1, nonblock);
 }
 #endif /* !_WIN32 */
 
@@ -569,7 +586,7 @@  static int stdio_nb_clients = 0;
 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(s->fd_out, buf, len, false);
 }
 
 static int fd_chr_read_poll(void *opaque)
@@ -881,7 +898,7 @@  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(s->fd, buf, len, false);
 }
 
 static int pty_chr_read_poll(void *opaque)
@@ -1946,7 +1963,7 @@  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);
+        return send_all(s->fd, buf, len, false);
     } else {
         /* XXX: indicate an error ? */
         return len;
diff --git a/qemu-char.h b/qemu-char.h
index 6ff490b..7b10b2b 100644
--- a/qemu-char.h
+++ b/qemu-char.h
@@ -1,6 +1,8 @@ 
 #ifndef QEMU_CHAR_H
 #define QEMU_CHAR_H
 
+#include <stdbool.h>
+
 #include "qemu-common.h"
 #include "qemu-queue.h"
 #include "qemu-option.h"
@@ -53,12 +55,15 @@  typedef void IOEventHandler(void *opaque, int event);
 struct CharDriverState {
     void (*init)(struct CharDriverState *s);
     int (*chr_write)(struct CharDriverState *s, const uint8_t *buf, int len);
+    ssize_t (*chr_write_nb)(struct CharDriverState *s, const uint8_t *buf,
+                            size_t len);
     void (*chr_update_read_handler)(struct CharDriverState *s);
     int (*chr_ioctl)(struct CharDriverState *s, int cmd, void *arg);
     int (*get_msgfd)(struct CharDriverState *s);
     IOEventHandler *chr_event;
     IOCanReadHandler *chr_can_read;
     IOReadHandler *chr_read;
+    IOHandler *chr_write_unblocked;
     void *handler_opaque;
     void (*chr_send_event)(struct CharDriverState *chr, int event);
     void (*chr_close)(struct CharDriverState *chr);
@@ -68,6 +73,8 @@  struct CharDriverState {
     char *label;
     char *filename;
     int opened;
+    bool nonblock;
+    bool write_blocked;
     QTAILQ_ENTRY(CharDriverState) next;
 };
 
@@ -85,6 +92,7 @@  CharDriverState *qemu_chr_open(const char *label, const char *filename, void (*i
 void qemu_chr_close(CharDriverState *chr);
 void qemu_chr_printf(CharDriverState *s, const char *fmt, ...);
 int qemu_chr_write(CharDriverState *s, const uint8_t *buf, int len);
+ssize_t qemu_chr_write_nb(CharDriverState *s, const uint8_t *buf, size_t len);
 void qemu_chr_send_event(CharDriverState *s, int event);
 void qemu_chr_add_handlers(CharDriverState *s, QemuChrHandlers *handlers,
                            void *opaque);
diff --git a/qemu_socket.h b/qemu_socket.h
index 164ae3e..bdf878b 100644
--- a/qemu_socket.h
+++ b/qemu_socket.h
@@ -23,6 +23,7 @@  int inet_aton(const char *cp, struct in_addr *ia);
 #include <arpa/inet.h>
 #include <netdb.h>
 #include <sys/un.h>
+#include <stdbool.h>
 
 #define socket_error() errno
 #define closesocket(s) close(s)
@@ -35,7 +36,7 @@  int inet_aton(const char *cp, struct in_addr *ia);
 int qemu_socket(int domain, int type, int protocol);
 int qemu_accept(int s, struct sockaddr *addr, socklen_t *addrlen);
 void socket_set_nonblock(int fd);
-int send_all(int fd, const void *buf, int len1);
+int send_all(int fd, const void *buf, int len1, bool nonblock);
 
 /* New, ipv6-ready socket helper functions, see qemu-sockets.c */
 int inet_listen_opts(QemuOpts *opts, int port_offset);