hw/block/pflash_cfi*.c: fix confusing assert fail message

The patch is to fix the confusing assert fail message caused by
un-initialized device structure (from bite sized tasks).

The bug can be reproduced by

./qemu-system-x86_64 -nographic -device cfi.pflash01

The CFI hardware is dynamically loaded by QOM realizing mechanism,
however the realizing function in pflash_cfi01_realize function
requires the device being initialized manually before calling, like

./qemu-system-x86_64 -nographic
-device cfi.pflash01,num-blocks=1024,sector-length=4096,name=testcard

Once the initializing parameters are left off in the command, it will
leave the device structure not initialized, which makes
pflash_cfi01_realize try to realize a zero-volume card, causing

/mnt/EXT_volume/projects/qemu/qemu-dev/exec.c:1378:
find_ram_offset: Assertion `size != 0\' failed.

Through my test, at least the flash device's block-number, sector-length
and its name is needed for pflash_cfi01_realize to behave correctly. So
I think the new asserts are needed to hint the QEMU user to specify
the device's parameters correctly.
Signed-off-by: NZiyue Yang <skiver.cloud.yzy@gmail.com>
Message-Id: <1481810693-13733-1-git-send-email-skiver.cloud.yzy@gmail.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: NZiyue Yang <yzylivezh@hotmail.com>

hw/block/pflash_cfi01.c

@@ -707,6 +707,19 @@ static void pflash_cfi01_realize(DeviceState *dev, Error **errp)
     int num_devices;
     Error *local_err = NULL;
 
+    if (pfl->sector_len == 0) {
+        error_setg(errp, "attribute \"sector-length\" not specified or zero.");
+        return;
+    }
+    if (pfl->nb_blocs == 0) {
+        error_setg(errp, "attribute \"num-blocks\" not specified or zero.");
+        return;
+    }
+    if (pfl->name == NULL) {
+        error_setg(errp, "attribute \"name\" not specified.");
+        return;
+    }
+
     total_len = pfl->sector_len * pfl->nb_blocs;
 
     /* These are only used to expose the parameters of each device

hw/block/pflash_cfi02.c

@@ -600,6 +600,19 @@ static void pflash_cfi02_realize(DeviceState *dev, Error **errp)
     int ret;
     Error *local_err = NULL;
 
+    if (pfl->sector_len == 0) {
+        error_setg(errp, "attribute \"sector-length\" not specified or zero.");
+        return;
+    }
+    if (pfl->nb_blocs == 0) {
+        error_setg(errp, "attribute \"num-blocks\" not specified or zero.");
+        return;
+    }
+    if (pfl->name == NULL) {
+        error_setg(errp, "attribute \"name\" not specified.");
+        return;
+    }
+
     chip_len = pfl->sector_len * pfl->nb_blocs;
     /* XXX: to be fixed */
 #if 0