On Wed, Jun 19, 2019 at 12:29:04PM +0300, Sam Eiderman wrote:
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 Signed-off-by: Sam Eiderman shmuel.eiderman@oracle.com
bootdevice.c | 32 ++++++++++++++++++++++++++++++++ hw/nvram/fw_cfg.c | 14 +++++++++++--- include/sysemu/sysemu.h | 1 + 3 files changed, 44 insertions(+), 3 deletions(-)
diff --git a/bootdevice.c b/bootdevice.c index 2b12fb85a4..b034ad7bdc 100644 --- a/bootdevice.c +++ b/bootdevice.c @@ -405,3 +405,35 @@ void del_boot_device_lchs(DeviceState *dev, const char *suffix) } } }
+/* Serialized as: (device name\0 + lchs struct) x devices */
Comment is outdated.
- 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);
Can fw_cfg_modify_file handle buf == NULL?
cheers, Gerd