[Qemu-devel] [RFC PATCH] hw/arm/virt: use variable size of flash device to save memory

[Xiang Zheng]

Currently we fill the VIRT_FLASH space with two 64MB NOR images when
using persistent UEFI variables on QEMU. Actually we only use a very
small part of the memory while the rest significant large part of
memory is wasted.

This patch creates and maps a variable size of flash device instead of
a mandatory 64MB one to save memory.

Signed-off-by: Xiang Zheng <address@hidden>
---

This patch might be insufficient since it also needs to modify the flash size
in ACPI and DTB.

BTW, I don't understand why it requires the two NOR images to be exactly 64MB
in size when using -pflash.

---
 hw/arm/virt.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/hw/arm/virt.c b/hw/arm/virt.c
index ce2664a..8269532 100644
--- a/hw/arm/virt.c
+++ b/hw/arm/virt.c
@@ -44,6 +44,7 @@
 #include "sysemu/numa.h"
 #include "sysemu/sysemu.h"
 #include "sysemu/kvm.h"
+#include "sysemu/block-backend.h"
 #include "hw/loader.h"
 #include "exec/address-spaces.h"
 #include "qemu/bitops.h"
@@ -881,14 +882,18 @@ static void create_one_flash(const char *name, hwaddr 
flashbase,
     DriveInfo *dinfo = drive_get_next(IF_PFLASH);
     DeviceState *dev = qdev_create(NULL, TYPE_PFLASH_CFI01);
     SysBusDevice *sbd = SYS_BUS_DEVICE(dev);
+    BlockBackend *blk_backend = NULL;
     const uint64_t sectorlength = 256 * 1024;
+    hwaddr real_size = flashsize;
 
     if (dinfo) {
-        qdev_prop_set_drive(dev, "drive", blk_by_legacy_dinfo(dinfo),
-                            &error_abort);
+        blk_backend = blk_by_legacy_dinfo(dinfo);
+        qdev_prop_set_drive(dev, "drive", blk_backend, &error_abort);
+        real_size = blk_getlength(blk_backend);
+        real_size = flashsize > real_size ? real_size : flashsize;
     }
 
-    qdev_prop_set_uint32(dev, "num-blocks", flashsize / sectorlength);
+    qdev_prop_set_uint32(dev, "num-blocks", real_size / sectorlength);
     qdev_prop_set_uint64(dev, "sector-length", sectorlength);
     qdev_prop_set_uint8(dev, "width", 4);
     qdev_prop_set_uint8(dev, "device-width", 2);
-- 
1.8.3.1