[RFC PATCH 3/3] hw/block/pflash: use memory_region_init_rom_device_from_file()

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

If the block drive is read-only we will model a "protected" flash
device. We can thus use memory_region_init_rom_device_from_file()
which mmap the backing file when creating the MemoryRegion.
If the same backing file is used by multiple QEMU instances, this
reduces the memory footprint (this is often the case with the
CODE flash image from OVMF and AAVMF).

Suggested-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
---
 hw/block/pflash_cfi01.c | 20 ++++++++++++++------
 hw/block/pflash_cfi02.c | 18 ++++++++++++++----
 2 files changed, 28 insertions(+), 10 deletions(-)

diff --git a/hw/block/pflash_cfi01.c b/hw/block/pflash_cfi01.c
index a5fa8d8b74a..5757391df1c 100644
--- a/hw/block/pflash_cfi01.c
+++ b/hw/block/pflash_cfi01.c
@@ -743,11 +743,19 @@ static void pflash_cfi01_realize(DeviceState *dev, Error **errp)
         pfl->ro = 0;
     }
 
-    memory_region_init_rom_device(
-        &pfl->mem, OBJECT(dev),
-        &pflash_cfi01_ops,
-        pfl,
-        pfl->name, total_len, errp);
+    if (pfl->blk && pfl->ro) {
+        memory_region_init_rom_device_from_file(&pfl->mem, OBJECT(dev),
+                                                &pflash_cfi01_ops, pfl,
+                                                pfl->name, total_len,
+                                                qemu_real_host_page_size,
+                                                RAM_SHARED,
+                                                blk_bs(pfl->blk)->filename,
+                                                true, errp);
+    } else {
+        memory_region_init_rom_device(&pfl->mem, OBJECT(dev),
+                                      &pflash_cfi01_ops, pfl,
+                                      pfl->name, total_len, errp);
+    }
     if (*errp) {
         return;
     }
@@ -755,7 +763,7 @@ static void pflash_cfi01_realize(DeviceState *dev, Error **errp)
     pfl->storage = memory_region_get_ram_ptr(&pfl->mem);
     sysbus_init_mmio(SYS_BUS_DEVICE(dev), &pfl->mem);
 
-    if (pfl->blk) {
+    if (pfl->blk && !pfl->ro) {
         if (!blk_check_size_and_read_all(pfl->blk, pfl->storage, total_len,
                                          errp)) {
             vmstate_unregister_ram(&pfl->mem, DEVICE(pfl));
diff --git a/hw/block/pflash_cfi02.c b/hw/block/pflash_cfi02.c
index 4f62ce8917d..d57f64d7732 100644
--- a/hw/block/pflash_cfi02.c
+++ b/hw/block/pflash_cfi02.c
@@ -803,16 +803,26 @@ static void pflash_cfi02_realize(DeviceState *dev, Error **errp)
         pfl->ro = 0;
     }
 
-    memory_region_init_rom_device(&pfl->orig_mem, OBJECT(pfl),
-                                  &pflash_cfi02_ops, pfl, pfl->name,
-                                  pfl->chip_len, errp);
+    if (pfl->blk && pfl->ro) {
+        memory_region_init_rom_device_from_file(&pfl->orig_mem, OBJECT(pfl),
+                                                &pflash_cfi02_ops, pfl,
+                                                pfl->name, pfl->chip_len,
+                                                qemu_real_host_page_size,
+                                                RAM_SHARED,
+                                                blk_bs(pfl->blk)->filename,
+                                                true, errp);
+    } else {
+        memory_region_init_rom_device(&pfl->orig_mem, OBJECT(pfl),
+                                      &pflash_cfi02_ops, pfl, pfl->name,
+                                      pfl->chip_len, errp);
+    }
     if (*errp) {
         return;
     }
 
     pfl->storage = memory_region_get_ram_ptr(&pfl->orig_mem);
 
-    if (pfl->blk) {
+    if (pfl->blk && !pfl->ro) {
         if (!blk_check_size_and_read_all(pfl->blk, pfl->storage,
                                          pfl->chip_len, errp)) {
             vmstate_unregister_ram(&pfl->orig_mem, DEVICE(pfl));
-- 
2.26.2