[Qemu-devel] [QEMU] [PATCH v4 7/8] bootdevice: FW_CFG interface for LCHS values

[Sam Eiderman <shmuel.eiderman@oracle.com>]

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 */
+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;
+}
diff --git a/hw/nvram/fw_cfg.c b/hw/nvram/fw_cfg.c
index 9f7b7789bc..c1230fe11c 100644
--- a/hw/nvram/fw_cfg.c
+++ b/hw/nvram/fw_cfg.c
@@ -916,13 +916,21 @@ 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)
diff --git a/include/sysemu/sysemu.h b/include/sysemu/sysemu.h
index 173dfbb539..1ca8799588 100644
--- a/include/sysemu/sysemu.h
+++ b/include/sysemu/sysemu.h
@@ -174,6 +174,7 @@ void validate_bootdevices(const char *devices, Error **errp);
 void add_boot_device_lchs(DeviceState *dev, const char *suffix,
                           uint32_t lcyls, uint32_t lheads, uint32_t lsecs);
 void del_boot_device_lchs(DeviceState *dev, const char *suffix);
+char *get_boot_devices_lchs_list(size_t *size);
 
 /* handler to set the boot_device order for a specific type of MachineClass */
 typedef void QEMUBootSetHandler(void *opaque, const char *boot_order,
-- 
2.13.3