socket shutdown

Add QEMUFile interface to allow a socket to be 'shut down' - i.e. any
reads/writes will fail (and any blocking read/write will be woken).

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Amit Shah <amit.shah@redhat.com>
Signed-off-by: Amit Shah <amit.shah@redhat.com>

include/migration/qemu-file.h

@@ -84,6 +84,14 @@ typedef size_t (QEMURamSaveFunc)(QEMUFile *f, void *opaque,
                                size_t size,
                                int *bytes_sent);
 
+/*
+ * Stop any read or write (depending on flags) on the underlying
+ * transport on the QEMUFile.
+ * Existing blocking reads/writes must be woken
+ * Returns 0 on success, -err on error
+ */
+typedef int (QEMUFileShutdownFunc)(void *opaque, bool rd, bool wr);
+
 typedef struct QEMUFileOps {
     QEMUFilePutBufferFunc *put_buffer;
     QEMUFileGetBufferFunc *get_buffer;
@@ -94,6 +102,7 @@ typedef struct QEMUFileOps {
     QEMURamHookFunc *after_ram_iterate;
     QEMURamHookFunc *hook_ram_load;
     QEMURamSaveFunc *save_page;
+    QEMUFileShutdownFunc *shut_down;
 } QEMUFileOps;
 
 struct QEMUSizedBuffer {
@@ -177,6 +186,7 @@ void qemu_file_set_rate_limit(QEMUFile *f, int64_t new_rate);
 int64_t qemu_file_get_rate_limit(QEMUFile *f);
 int qemu_file_get_error(QEMUFile *f);
 void qemu_file_set_error(QEMUFile *f, int ret);
+int qemu_file_shutdown(QEMUFile *f);
 void qemu_fflush(QEMUFile *f);
 
 static inline void qemu_put_be64s(QEMUFile *f, const uint64_t *pv)

include/qemu/sockets.h

@@ -44,6 +44,13 @@ int socket_set_fast_reuse(int fd);
 int send_all(int fd, const void *buf, int len1);
 int recv_all(int fd, void *buf, int len1, bool single_read);
 
+#ifdef WIN32
+/* Windows has different names for the same constants with the same values */
+#define SHUT_RD   0
+#define SHUT_WR   1
+#define SHUT_RDWR 2
+#endif
+
 /* callback function for nonblocking connect
  * valid fd on success, negative error code on failure
  */

migration/qemu-file-unix.c

@@ -26,6 +26,7 @@
 #include "qemu/sockets.h"
 #include "block/coroutine.h"
 #include "migration/qemu-file.h"
+#include "migration/qemu-file-internal.h"
 
 typedef struct QEMUFileSocket {
     int fd;
@@ -84,6 +85,17 @@ static int socket_close(void *opaque)
     return 0;
 }
 
+static int socket_shutdown(void *opaque, bool rd, bool wr)
+{
+    QEMUFileSocket *s = opaque;
+
+    if (shutdown(s->fd, rd ? (wr ? SHUT_RDWR : SHUT_RD) : SHUT_WR)) {
+        return -errno;
+    } else {
+        return 0;
+    }
+}
+
 static ssize_t unix_writev_buffer(void *opaque, struct iovec *iov, int iovcnt,
                                   int64_t pos)
 {
@@ -192,15 +204,18 @@ QEMUFile *qemu_fdopen(int fd, const char *mode)
 }
 
 static const QEMUFileOps socket_read_ops = {
-    .get_fd =     socket_get_fd,
+    .get_fd     = socket_get_fd,
     .get_buffer = socket_get_buffer,
-    .close =      socket_close
+    .close      = socket_close,
+    .shut_down  = socket_shutdown
+
 };
 
 static const QEMUFileOps socket_write_ops = {
-    .get_fd =     socket_get_fd,
+    .get_fd        = socket_get_fd,
     .writev_buffer = socket_writev_buffer,
-    .close =      socket_close
+    .close         = socket_close,
+    .shut_down     = socket_shutdown
 };
 
 QEMUFile *qemu_fopen_socket(int fd, const char *mode)

migration/qemu-file.c

@@ -30,6 +30,18 @@
 #include "migration/qemu-file-internal.h"
 #include "trace.h"
 
+/*
+ * Stop a file from being read/written - not all backing files can do this
+ * typically only sockets can.
+ */
+int qemu_file_shutdown(QEMUFile *f)
+{
+    if (!f->ops->shut_down) {
+        return -ENOSYS;
+    }
+    return f->ops->shut_down(f->opaque, true, true);
+}
+
 bool qemu_file_mode_is_not_valid(const char *mode)
 {
     if (mode == NULL ||