blockdev: Fix drive_add for drives without media

Watch this:

    (qemu) drive_add 0 if=none
    (qemu) info block
    none0: type=hd removable=0 [not inserted]
    (qemu) drive_del none0
    Segmentation fault (core dumped)

add_init_drive() is confused about drive_init()'s failure modes, and
cleans up when it shouldn't.  This leaves the DriveInfo with member
opts dangling.  drive_del attempts to free it, and dies.

drive_init() behaves as follows:

* If it created a drive with media, it returns its DriveInfo.

* If it created a drive without media, it clears *fatal_error and
  returns NULL.

* If it couldn't create a drive, it sets *fatal_error and returns
  NULL.

Of its three callers:

* drive_init_func() is correct.

* usb_msd_init() assumes drive_init() failed when it returns NULL.
  This is correct only because it always passes option "file", and
  "drive without media" can't happen then.

* add_init_drive() assumes drive_init() failed when it returns NULL.
  This is incorrect.

Clean up drive_init() to return NULL on failure and only on failure.
Drop its parameter fatal_error.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

2 files changed, 2 insertions, 4 deletions

diff --git a/hw/device-hotplug.c b/hw/device-hotplug.c
index 95a63726f3..8b2ed7a492 100644
--- a/hw/device-hotplug.c
+++ b/hw/device-hotplug.c
@@ -29,7 +29,6 @@
 
 DriveInfo *add_init_drive(const char *optstr)
 {
-    int fatal_error;
     DriveInfo *dinfo;
     QemuOpts *opts;
 
@@ -37,7 +36,7 @@ DriveInfo *add_init_drive(const char *optstr)
     if (!opts)
         return NULL;
 
-    dinfo = drive_init(opts, current_machine->use_scsi, &fatal_error);
+    dinfo = drive_init(opts, current_machine->use_scsi);
     if (!dinfo) {
         qemu_opts_del(opts);
         return NULL;
diff --git a/hw/usb-msd.c b/hw/usb-msd.c
index 11722c7486..97d1e4af13 100644
--- a/hw/usb-msd.c
+++ b/hw/usb-msd.c
@@ -542,7 +542,6 @@ static USBDevice *usb_msd_init(const char *filename)
     QemuOpts *opts;
     DriveInfo *dinfo;
     USBDevice *dev;
-    int fatal_error;
     const char *p1;
     char fmt[32];
 
@@ -572,7 +571,7 @@ static USBDevice *usb_msd_init(const char *filename)
     qemu_opt_set(opts, "if", "none");
 
     /* create host drive */
-    dinfo = drive_init(opts, 0, &fatal_error);
+    dinfo = drive_init(opts, 0);
     if (!dinfo) {
         qemu_opts_del(opts);
         return NULL;