[Qemu-devel] [RFC PATCH v6 4/4] fixup! hw/block: Pad undersized read-only images with 0xFF

[Markus Armbruster <armbru@redhat.com>]

---
 hw/block/pflash_cfi02.c | 22 +++++++++++++++++-----
 1 file changed, 17 insertions(+), 5 deletions(-)

diff --git a/hw/block/pflash_cfi02.c b/hw/block/pflash_cfi02.c
index d30a351472..db1c39499c 100644
--- a/hw/block/pflash_cfi02.c
+++ b/hw/block/pflash_cfi02.c
@@ -578,8 +578,9 @@ static void pflash_cfi02_realize(DeviceState *dev, Error **errp)
     if (pfl->blk) {
         /*
          * Validate the backing store is the right size for pflash
-         * devices. If the user supplies a larger file we ignore the
-         * tail.
+         * devices. If the device is read-only we can elide the check
+         * and just pad the region first. If the user supplies a
+         * larger file we ignore the tail.
          */
         int64_t backing_len = blk_getlength(pfl->blk);
         if (backing_len < 0) {
@@ -588,9 +589,20 @@ static void pflash_cfi02_realize(DeviceState *dev, Error **errp)
         }
 
         if (backing_len < chip_len) {
-            error_setg(errp, "device needs %" PRIu32 " bytes, "
-                       "backing file provides only %" PRIu64 " bytes",
-                       chip_len, backing_len);
+            if (pfl->ro) {
+                size_t pad_bytes = chip_len - backing_len;
+                /* pad with NOR erase pattern */
+                memset((uint8_t *)pfl->storage + backing_len,
+                       0xff, pad_bytes);
+                warn_report("device needs %" PRIu32
+                            " bytes, padded with %zu 0xff bytes",
+                            chip_len, pad_bytes);
+                chip_len = backing_len;
+            } else {
+                error_setg(errp, "device needs %" PRIu32 " bytes, "
+                           "backing file provides only %" PRIu64 " bytes",
+                           chip_len, backing_len);
+            }
             return;
         } else if (backing_len > chip_len) {
             warn_report("device needs %" PRIu32 " bytes, rest ignored",
-- 
2.17.2