ide: fail I/O to empty disk

Requesting a read or a write operation on an empty disk can lead
to QEMU dumping core.

Also fix a few braces here and there.
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
Reviewed-by: NStefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

hw/ide/core.c

@@ -1068,6 +1068,9 @@ void ide_exec_cmd(IDEBus *bus, uint32_t val)
             ide_set_signature(s); /* odd, but ATA4 8.27.5.2 requires it */
             goto abort_cmd;
         }
+        if (!s->bs) {
+            goto abort_cmd;
+        }
 	ide_cmd_lba48_transform(s, lba48);
         s->req_nb_sectors = 1;
         ide_sector_read(s);
@@ -1078,6 +1081,9 @@ void ide_exec_cmd(IDEBus *bus, uint32_t val)
     case WIN_WRITE_ONCE:
     case CFA_WRITE_SECT_WO_ERASE:
     case WIN_WRITE_VERIFY:
+        if (!s->bs) {
+            goto abort_cmd;
+        }
 	ide_cmd_lba48_transform(s, lba48);
         s->error = 0;
         s->status = SEEK_STAT | READY_STAT;
@@ -1088,8 +1094,12 @@ void ide_exec_cmd(IDEBus *bus, uint32_t val)
     case WIN_MULTREAD_EXT:
 	lba48 = 1;
     case WIN_MULTREAD:
-        if (!s->mult_sectors)
+        if (!s->bs) {
             goto abort_cmd;
+        }
+        if (!s->mult_sectors) {
+            goto abort_cmd;
+        }
 	ide_cmd_lba48_transform(s, lba48);
         s->req_nb_sectors = s->mult_sectors;
         ide_sector_read(s);
@@ -1098,8 +1108,12 @@ void ide_exec_cmd(IDEBus *bus, uint32_t val)
 	lba48 = 1;
     case WIN_MULTWRITE:
     case CFA_WRITE_MULTI_WO_ERASE:
-        if (!s->mult_sectors)
+        if (!s->bs) {
             goto abort_cmd;
+        }
+        if (!s->mult_sectors) {
+            goto abort_cmd;
+        }
 	ide_cmd_lba48_transform(s, lba48);
         s->error = 0;
         s->status = SEEK_STAT | READY_STAT;
@@ -1114,8 +1128,9 @@ void ide_exec_cmd(IDEBus *bus, uint32_t val)
 	lba48 = 1;
     case WIN_READDMA:
     case WIN_READDMA_ONCE:
-        if (!s->bs)
+        if (!s->bs) {
             goto abort_cmd;
+        }
 	ide_cmd_lba48_transform(s, lba48);
         ide_sector_start_dma(s, IDE_DMA_READ);
         break;
@@ -1123,8 +1138,9 @@ void ide_exec_cmd(IDEBus *bus, uint32_t val)
 	lba48 = 1;
     case WIN_WRITEDMA:
     case WIN_WRITEDMA_ONCE:
-        if (!s->bs)
+        if (!s->bs) {
             goto abort_cmd;
+        }
 	ide_cmd_lba48_transform(s, lba48);
         ide_sector_start_dma(s, IDE_DMA_WRITE);
         s->media_changed = 1;