bootdevice: FW_CFG interface for LCHS values

Using fw_cfg, supply logical CHS values directly from QEMU to the BIOS.

Non-standard logical geometries break under QEMU.

A virtual disk which contains an operating system which depends on
logical geometries (consistent values being reported from BIOS INT13
AH=08) will most likely break under QEMU/SeaBIOS if it has non-standard
logical geometries - for example 56 SPT (sectors per track).
No matter what QEMU will report - SeaBIOS, for large enough disks - will
use LBA translation, which will report 63 SPT instead.

In addition we cannot force SeaBIOS to rely on physical geometries at
all. A virtio-blk-pci virtual disk with 255 phyiscal heads cannot
report more than 16 physical heads when moved to an IDE controller,
since the ATA spec allows a maximum of 16 heads - this is an artifact of
virtualization.

By supplying the logical geometries directly we are able to support such
"exotic" disks.

We serialize this information in a similar way to the "bootorder"
interface.
The new fw_cfg entry is "bios-geometry".

Reviewed-by: Karl Heubaum <karl.heubaum@oracle.com>
Reviewed-by: Arbel Moshe <arbel.moshe@oracle.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Sam Eiderman <shmuel.eiderman@oracle.com>
Signed-off-by: Sam Eiderman <sameid@google.com>
Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: John Snow <jsnow@redhat.com>

1 files changed, 11 insertions, 3 deletions

diff --git a/hw/nvram/fw_cfg.c b/hw/nvram/fw_cfg.c
index aef1727..44a3c19 100644
--- a/hw/nvram/fw_cfg.c
+++ b/hw/nvram/fw_cfg.c
@@ -949,13 +949,21 @@ void *fw_cfg_modify_file(FWCfgState *s, const char *filename,
 
 static void fw_cfg_machine_reset(void *opaque)
 {
+    MachineClass *mc = MACHINE_GET_CLASS(qdev_get_machine());
+    FWCfgState *s = opaque;
     void *ptr;
     size_t len;
-    FWCfgState *s = opaque;
-    char *bootindex = get_boot_devices_list(&len);
+    char *buf;
 
-    ptr = fw_cfg_modify_file(s, "bootorder", (uint8_t *)bootindex, len);
+    buf = get_boot_devices_list(&len);
+    ptr = fw_cfg_modify_file(s, "bootorder", (uint8_t *)buf, len);
     g_free(ptr);
+
+    if (!mc->legacy_fw_cfg_order) {
+        buf = get_boot_devices_lchs_list(&len);
+        ptr = fw_cfg_modify_file(s, "bios-geometry", (uint8_t *)buf, len);
+        g_free(ptr);
+    }
 }
 
 static void fw_cfg_machine_ready(struct Notifier *n, void *data)