loader: add rom transaction API

Image file loaders may add a series of roms.  If an error occurs partway
through loading there is no easy way to drop previously added roms.

This patch adds a transaction mechanism that works like this:

  rom_transaction_begin();
  ...call rom_add_*()...
  rom_transaction_end(ok);

If ok is false then roms added in this transaction are dropped.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-id: 20180814162739.11814-5-stefanha@redhat.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

hw/core/loader.c

@@ -840,6 +840,8 @@ struct Rom {
     char *fw_dir;
     char *fw_file;
 
+    bool committed;
+
     hwaddr addr;
     QTAILQ_ENTRY(Rom) next;
 };
@@ -877,6 +879,8 @@ static void rom_insert(Rom *rom)
         rom->as = &address_space_memory;
     }
 
+    rom->committed = false;
+
     /* List is ordered by load address in the same address space */
     QTAILQ_FOREACH(item, &roms, next) {
         if (rom_order_compare(rom, item)) {
@@ -1168,6 +1172,34 @@ void rom_reset_order_override(void)
     fw_cfg_reset_order_override(fw_cfg);
 }
 
+void rom_transaction_begin(void)
+{
+    Rom *rom;
+
+    /* Ignore ROMs added without the transaction API */
+    QTAILQ_FOREACH(rom, &roms, next) {
+        rom->committed = true;
+    }
+}
+
+void rom_transaction_end(bool commit)
+{
+    Rom *rom;
+    Rom *tmp;
+
+    QTAILQ_FOREACH_SAFE(rom, &roms, next, tmp) {
+        if (rom->committed) {
+            continue;
+        }
+        if (commit) {
+            rom->committed = true;
+        } else {
+            QTAILQ_REMOVE(&roms, rom, next);
+            rom_free(rom);
+        }
+    }
+}
+
 static Rom *find_rom(hwaddr addr, size_t size)
 {
     Rom *rom;

include/hw/loader.h

@@ -225,6 +225,25 @@ int rom_check_and_register_reset(void);
 void rom_set_fw(FWCfgState *f);
 void rom_set_order_override(int order);
 void rom_reset_order_override(void);
+
+/**
+ * rom_transaction_begin:
+ *
+ * Call this before of a series of rom_add_*() calls.  Call
+ * rom_transaction_end() afterwards to commit or abort.  These functions are
+ * useful for undoing a series of rom_add_*() calls if image file loading fails
+ * partway through.
+ */
+void rom_transaction_begin(void);
+
+/**
+ * rom_transaction_end:
+ * @commit: true to commit added roms, false to drop added roms
+ *
+ * Call this after a series of rom_add_*() calls.  See rom_transaction_begin().
+ */
+void rom_transaction_end(bool commit);
+
 int rom_copy(uint8_t *dest, hwaddr addr, size_t size);
 void *rom_ptr(hwaddr addr, size_t size);
 void hmp_info_roms(Monitor *mon, const QDict *qdict);