io: Introduce qio_channel_file_new_dupfd

Add a new helper function for creating a QIOChannelFile channel with a
duplicated file descriptor. This saves the calling code from having to
do error checking on the dup() call.

Suggested-by: "Daniel P. Berrangé" <berrange@redhat.com>
Signed-off-by: Fabiano Rosas <farosas@suse.de>
Reviewed-by: "Daniel P. Berrangé" <berrange@redhat.com>
Link: https://lore.kernel.org/r/20240311233335.17299-2-farosas@suse.de
Signed-off-by: Peter Xu <peterx@redhat.com>

include/io/channel-file.h

@@ -68,6 +68,24 @@ struct QIOChannelFile {
 QIOChannelFile *
 qio_channel_file_new_fd(int fd);
 
+/**
+ * qio_channel_file_new_dupfd:
+ * @fd: the file descriptor
+ * @errp: pointer to initialized error object
+ *
+ * Create a new IO channel object for a file represented by the @fd
+ * parameter. Like qio_channel_file_new_fd(), but the @fd is first
+ * duplicated with dup().
+ *
+ * The channel will own the duplicated file descriptor and will take
+ * responsibility for closing it, the original FD is owned by the
+ * caller.
+ *
+ * Returns: the new channel object
+ */
+QIOChannelFile *
+qio_channel_file_new_dupfd(int fd, Error **errp);
+
 /**
  * qio_channel_file_new_path:
  * @path: the file path

io/channel-file.c

@@ -45,6 +45,18 @@ qio_channel_file_new_fd(int fd)
     return ioc;
 }
 
+QIOChannelFile *
+qio_channel_file_new_dupfd(int fd, Error **errp)
+{
+    int newfd = dup(fd);
+
+    if (newfd < 0) {
+        error_setg_errno(errp, errno, "Could not dup FD %d", fd);
+        return NULL;
+    }
+
+    return qio_channel_file_new_fd(newfd);
+}
 
 QIOChannelFile *
 qio_channel_file_new_path(const char *path,