migration: add qemu_get_fd

Reviewed-by: Orit Wasserman <owasserm@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

buffered_file.c

@@ -174,6 +174,13 @@ static int buffered_close(void *opaque)
  *   1: Time to stop
  *   negative: There has been an error
  */
+static int buffered_get_fd(void *opaque)
+{
+    QEMUFileBuffered *s = opaque;
+
+    return qemu_get_fd(s->file);
+}
+
 static int buffered_rate_limit(void *opaque)
 {
     QEMUFileBuffered *s = opaque;
@@ -235,6 +242,7 @@ static void buffered_rate_tick(void *opaque)
 }
 
 static const QEMUFileOps buffered_file_ops = {
+    .get_fd =         buffered_get_fd,
     .put_buffer =     buffered_put_buffer,
     .close =          buffered_close,
     .rate_limit =     buffered_rate_limit,

qemu-file.h

@@ -47,6 +47,10 @@ typedef int (QEMUFileGetBufferFunc)(void *opaque, uint8_t *buf,
  */
 typedef int (QEMUFileCloseFunc)(void *opaque);
 
+/* Called to return the OS file descriptor associated to the QEMUFile.
+ */
+typedef int (QEMUFileGetFD)(void *opaque);
+
 /* Called to determine if the file has exceeded its bandwidth allocation.  The
  * bandwidth capping is a soft limit, not a hard limit.
  */
@@ -63,6 +67,7 @@ typedef struct QEMUFileOps {
     QEMUFilePutBufferFunc *put_buffer;
     QEMUFileGetBufferFunc *get_buffer;
     QEMUFileCloseFunc *close;
+    QEMUFileGetFD *get_fd;
     QEMUFileRateLimit *rate_limit;
     QEMUFileSetRateLimit *set_rate_limit;
     QEMUFileGetRateLimit *get_rate_limit;
@@ -74,6 +79,7 @@ QEMUFile *qemu_fdopen(int fd, const char *mode);
 QEMUFile *qemu_fopen_socket(int fd);
 QEMUFile *qemu_popen(FILE *popen_file, const char *mode);
 QEMUFile *qemu_popen_cmd(const char *command, const char *mode);
+int qemu_get_fd(QEMUFile *f);
 int qemu_stdio_fd(QEMUFile *f);
 int qemu_fclose(QEMUFile *f);
 void qemu_put_buffer(QEMUFile *f, const uint8_t *buf, int size);

savevm.c

@@ -188,6 +188,13 @@ typedef struct QEMUFileSocket
     QEMUFile *file;
 } QEMUFileSocket;
 
+static int socket_get_fd(void *opaque)
+{
+    QEMUFileSocket *s = opaque;
+
+    return s->fd;
+}
+
 static int socket_get_buffer(void *opaque, uint8_t *buf, int64_t pos, int size)
 {
     QEMUFileSocket *s = opaque;
@@ -210,6 +217,13 @@ static int socket_close(void *opaque)
     return 0;
 }
 
+static int stdio_get_fd(void *opaque)
+{
+    QEMUFileStdio *s = opaque;
+
+    return fileno(s->stdio_file);
+}
+
 static int stdio_put_buffer(void *opaque, const uint8_t *buf, int64_t pos, int size)
 {
     QEMUFileStdio *s = opaque;
@@ -253,11 +267,13 @@ static int stdio_fclose(void *opaque)
 }
 
 static const QEMUFileOps stdio_pipe_read_ops = {
+    .get_fd =     stdio_get_fd,
     .get_buffer = stdio_get_buffer,
     .close =      stdio_pclose
 };
 
 static const QEMUFileOps stdio_pipe_write_ops = {
+    .get_fd =     stdio_get_fd,
     .put_buffer = stdio_put_buffer,
     .close =      stdio_pclose
 };
@@ -307,11 +323,13 @@ int qemu_stdio_fd(QEMUFile *f)
 }
 
 static const QEMUFileOps stdio_file_read_ops = {
+    .get_fd =     stdio_get_fd,
     .get_buffer = stdio_get_buffer,
     .close =      stdio_fclose
 };
 
 static const QEMUFileOps stdio_file_write_ops = {
+    .get_fd =     stdio_get_fd,
     .put_buffer = stdio_put_buffer,
     .close =      stdio_fclose
 };
@@ -345,6 +363,7 @@ fail:
 }
 
 static const QEMUFileOps socket_read_ops = {
+    .get_fd =     socket_get_fd,
     .get_buffer = socket_get_buffer,
     .close =      socket_close
 };
@@ -492,6 +511,14 @@ static void qemu_fill_buffer(QEMUFile *f)
         qemu_file_set_error(f, len);
 }
 
+int qemu_get_fd(QEMUFile *f)
+{
+    if (f->ops->get_fd) {
+        return f->ops->get_fd(f->opaque);
+    }
+    return -1;
+}
+
 /** Closes the file
  *
  * Returns negative error value if any error happened on previous operations or