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, 31 insertions, 0 deletions

diff --git a/bootdevice.c b/bootdevice.c
index 2cf6b37c57..03aaffcc8d 100644
--- a/bootdevice.c
+++ b/bootdevice.c
@@ -405,3 +405,34 @@ void del_boot_device_lchs(DeviceState *dev, const char *suffix)
         }
     }
 }
+
+char *get_boot_devices_lchs_list(size_t *size)
+{
+    FWLCHSEntry *i;
+    size_t total = 0;
+    char *list = NULL;
+
+    QTAILQ_FOREACH(i, &fw_lchs, link) {
+        char *bootpath;
+        char *chs_string;
+        size_t len;
+
+        bootpath = get_boot_device_path(i->dev, false, i->suffix);
+        chs_string = g_strdup_printf("%s %" PRIu32 " %" PRIu32 " %" PRIu32,
+                                     bootpath, i->lcyls, i->lheads, i->lsecs);
+
+        if (total) {
+            list[total - 1] = '\n';
+        }
+        len = strlen(chs_string) + 1;
+        list = g_realloc(list, total + len);
+        memcpy(&list[total], chs_string, len);
+        total += len;
+        g_free(chs_string);
+        g_free(bootpath);
+    }
+
+    *size = total;
+
+    return list;
+}