[Qemu-devel] [qemu PATCH] hw/i386/pc_sysfw: support more than one flash drive

[Laszlo Ersek <lersek@redhat.com>]

This patch allows the user to usefully specify

  -drive file=img_1,if=pflash,format=raw,readonly \
  -drive file=img_2,if=pflash,format=raw

on the command line. The flash images will be mapped under 4G in their
reverse unit order -- that is, with their base addresses progressing
downwards, in increasing unit order.

(The unit number increases with command line order if not explicitly
specified.)

This accommodates the following use case: suppose that OVMF is split in
two parts, a writeable host file for non-volatile variable storage, and a
read-only part for bootstrap and decompressible executable code.

The binary code part would be read-only, centrally managed on the host
system, and passed in as unit 0. The variable store would be writeable,
VM-specific, and passed in as unit 1.

  00000000ffe00000-00000000ffe1ffff (prio 0, R-): system.flash1
  00000000ffe20000-00000000ffffffff (prio 0, R-): system.flash0

(If the guest tries to write to the flash range that is backed by the
read-only drive, bdrv_write() in pflash_update() will correctly deny the
write with -EACCES, and pflash_update() won't care, which suits us well.)

Signed-off-by: Laszlo Ersek <lersek@redhat.com>
---
 hw/i386/pc_sysfw.c | 60 ++++++++++++++++++++++++++++++++++++++++--------------
 1 file changed, 45 insertions(+), 15 deletions(-)

diff --git a/hw/i386/pc_sysfw.c b/hw/i386/pc_sysfw.c
index e917c83..1c3e3d6 100644
--- a/hw/i386/pc_sysfw.c
+++ b/hw/i386/pc_sysfw.c
@@ -72,35 +72,65 @@ static void pc_isa_bios_init(MemoryRegion *rom_memory,
     memory_region_set_readonly(isa_bios, true);
 }
 
+/* This function maps flash drives from 4G downward, in order of their unit
+ * numbers. Addressing within one flash drive is of course not reversed.
+ *
+ * The drive with unit number 0 is mapped at the highest address, and it is
+ * passed to pc_isa_bios_init(). Merging severral drives for isa-bios is not
+ * supported.
+ *
+ * The caller is responsible to pass in the non-NULL @pflash_drv that
+ * corresponds to the flash drive with unit number 0.
+ */
 static void pc_system_flash_init(MemoryRegion *rom_memory,
                                  DriveInfo *pflash_drv)
 {
+    int unit = 0;
     BlockDriverState *bdrv;
     int64_t size;
-    hwaddr phys_addr;
+    hwaddr phys_addr = 0x100000000ULL;
     int sector_bits, sector_size;
     pflash_t *system_flash;
     MemoryRegion *flash_mem;
+    char name[64];
 
-    bdrv = pflash_drv->bdrv;
-    size = bdrv_getlength(pflash_drv->bdrv);
     sector_bits = 12;
     sector_size = 1 << sector_bits;
 
-    if ((size % sector_size) != 0) {
-        fprintf(stderr,
-                "qemu: PC system firmware (pflash) must be a multiple of 0x%x\n",
-                sector_size);
-        exit(1);
-    }
+    do {
+        bdrv = pflash_drv->bdrv;
+        size = bdrv_getlength(bdrv);
+        if ((size % sector_size) != 0) {
+            fprintf(stderr,
+                    "qemu: PC system firmware (pflash segment %d) must be a "
+                    "multiple of 0x%x\n", unit, sector_size);
+            exit(1);
+        }
+        if (size > phys_addr) {
+            fprintf(stderr, "qemu: pflash segments must fit under 4G "
+                    "cumulatively\n");
+            exit(1);
+        }
 
-    phys_addr = 0x100000000ULL - size;
-    system_flash = pflash_cfi01_register(phys_addr, NULL, "system.flash", size,
-                                         bdrv, sector_size, size >> sector_bits,
-                                         1, 0x0000, 0x0000, 0x0000, 0x0000, 0);
-    flash_mem = pflash_cfi01_get_memory(system_flash);
+        phys_addr -= size;
 
-    pc_isa_bios_init(rom_memory, flash_mem, size);
+        /* pflash_cfi01_register() creates a deep copy of the name */
+        snprintf(name, sizeof name, "system.flash%d", unit);
+        system_flash = pflash_cfi01_register(phys_addr, NULL /* qdev */, name,
+                                             size, bdrv, sector_size,
+                                             size >> sector_bits,
+                                             1      /* width */,
+                                             0x0000 /* id0 */,
+                                             0x0000 /* id1 */,
+                                             0x0000 /* id2 */,
+                                             0x0000 /* id3 */,
+                                             0      /* be */);
+        if (unit == 0) {
+            flash_mem = pflash_cfi01_get_memory(system_flash);
+            pc_isa_bios_init(rom_memory, flash_mem, size);
+        }
+        pflash_drv = drive_get(IF_PFLASH, 0, ++unit);
+    } while (pflash_drv != NULL);
 }
 
 static void old_pc_system_rom_init(MemoryRegion *rom_memory, bool isapc_ram_fw)
-- 
1.8.3.1