1 files changed, 43 insertions, 2 deletions

diff --git a/migration/file.c b/migration/file.c
index 0a65c43fdd..cf5b1bf365 100644
--- a/migration/file.c
+++ b/migration/file.c
@@ -6,6 +6,8 @@
  */
 
 #include "qemu/osdep.h"
+#include "qemu/cutils.h"
+#include "qapi/error.h"
 #include "channel.h"
 #include "file.h"
 #include "migration.h"
@@ -13,14 +15,41 @@
 #include "io/channel-util.h"
 #include "trace.h"
 
-void file_start_outgoing_migration(MigrationState *s, const char *filename,
+#define OFFSET_OPTION ",offset="
+
+/* Remove the offset option from @filespec and return it in @offsetp. */
+
+static int file_parse_offset(char *filespec, uint64_t *offsetp, Error **errp)
+{
+    char *option = strstr(filespec, OFFSET_OPTION);
+    int ret;
+
+    if (option) {
+        *option = 0;
+        option += sizeof(OFFSET_OPTION) - 1;
+        ret = qemu_strtosz(option, NULL, offsetp);
+        if (ret) {
+            error_setg_errno(errp, -ret, "file URI has bad offset %s", option);
+            return -1;
+        }
+    }
+    return 0;
+}
+
+void file_start_outgoing_migration(MigrationState *s, const char *filespec,
                                    Error **errp)
 {
+    g_autofree char *filename = g_strdup(filespec);
     g_autoptr(QIOChannelFile) fioc = NULL;
+    uint64_t offset = 0;
     QIOChannel *ioc;
 
     trace_migration_file_outgoing(filename);
 
+    if (file_parse_offset(filename, &offset, errp)) {
+        return;
+    }
+
     fioc = qio_channel_file_new_path(filename, O_CREAT | O_WRONLY | O_TRUNC,
                                      0600, errp);
     if (!fioc) {
@@ -28,6 +57,9 @@ void file_start_outgoing_migration(MigrationState *s, const char *filename,
     }
 
     ioc = QIO_CHANNEL(fioc);
+    if (offset && qio_channel_io_seek(ioc, offset, SEEK_SET, errp) < 0) {
+        return;
+    }
     qio_channel_set_name(ioc, "migration-file-outgoing");
     migration_channel_connect(s, ioc, NULL, NULL);
 }
@@ -41,19 +73,28 @@ static gboolean file_accept_incoming_migration(QIOChannel *ioc,
     return G_SOURCE_REMOVE;
 }
 
-void file_start_incoming_migration(const char *filename, Error **errp)
+void file_start_incoming_migration(const char *filespec, Error **errp)
 {
+    g_autofree char *filename = g_strdup(filespec);
     QIOChannelFile *fioc = NULL;
+    uint64_t offset = 0;
     QIOChannel *ioc;
 
     trace_migration_file_incoming(filename);
 
+    if (file_parse_offset(filename, &offset, errp)) {
+        return;
+    }
+
     fioc = qio_channel_file_new_path(filename, O_RDONLY, 0, errp);
     if (!fioc) {
         return;
     }
 
     ioc = QIO_CHANNEL(fioc);
+    if (offset && qio_channel_io_seek(ioc, offset, SEEK_SET, errp) < 0) {
+        return;
+    }
     qio_channel_set_name(QIO_CHANNEL(ioc), "migration-file-incoming");
     qio_channel_add_watch_full(ioc, G_IO_IN,
                                file_accept_incoming_migration,