preadv is going to be needed when 'fixed-ram'-enabled stream are to be
restored. Simply add a wrapper around preadv that's specific to
QIOChannelFile.

Signed-off-by: Nikolay Borisov <nborisov@suse.com>
---
 include/io/channel-file.h |  5 +++++
 io/channel-file.c         | 26 ++++++++++++++++++++++++++
 2 files changed, 31 insertions(+)

diff --git a/include/io/channel-file.h b/include/io/channel-file.h
index 0a5d54f5e58e..2187f5affd23 100644
--- a/include/io/channel-file.h
+++ b/include/io/channel-file.h
@@ -89,6 +89,11 @@ qio_channel_file_new_path(const char *path,
                           mode_t mode,
                           Error **errp);
 
+ssize_t qio_channel_file_preadv(QIOChannel *ioc,
+			       const struct iovec *iov,
+			       size_t niov,
+			       off_t offset,
+			       Error **errp);
 ssize_t qio_channel_file_pwritev(QIOChannel *ioc,
 				 const struct iovec *iov,
 				 size_t niov,
diff --git a/io/channel-file.c b/io/channel-file.c
index d84a6737f2f7..edca64ad63a7 100644
--- a/io/channel-file.c
+++ b/io/channel-file.c
@@ -141,6 +141,32 @@ static ssize_t qio_channel_file_writev(QIOChannel *ioc,
     return ret;
 }
 
+ssize_t qio_channel_file_preadv(QIOChannel *ioc,
+			       const struct iovec *iov,
+			       size_t niov,
+			       off_t offset,
+			       Error **errp)
+{
+    QIOChannelFile *fioc = QIO_CHANNEL_FILE(ioc);
+    ssize_t ret;
+
+ retry:
+    ret = preadv(fioc->fd, iov, niov, offset);
+    if (ret < 0) {
+        if (errno == EAGAIN) {
+            return QIO_CHANNEL_ERR_BLOCK;
+        }
+        if (errno == EINTR) {
+            goto retry;
+        }
+
+        error_setg_errno(errp, errno, "Unable to read from file");
+        return -1;
+    }
+
+    return ret;
+}
+
 ssize_t qio_channel_file_pwritev(QIOChannel *ioc,
 				 const struct iovec *iov,
 				 size_t niov,
-- 
2.34.1