dmg: fix ->open failure

Currently the dmg image format driver simply opens the images as raw
if any kind of failure happens.  This is contrarty to the behaviour
of all other image formats which just return an error and let the
block core deal with it.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

block/dmg.c

diff --git a/block/dmg.c b/block/dmg.c
index 262560f..f4c01c7 100644
--- a/block/dmg.c
+++ b/block/dmg.c
@@ -90,24 +90,21 @@
 
     /* read offset of info blocks */
     if(lseek(s->fd,-0x1d8,SEEK_END)<0) {
-dmg_close:
-	close(s->fd);
-	/* open raw instead */
-	bs->drv=bdrv_find_format("raw");
-	return bs->drv->bdrv_open(bs, filename, flags);
+        goto fail;
     }
+
     info_begin=read_off(s->fd);
     if(info_begin==0)
-	goto dmg_close;
+	goto fail;
     if(lseek(s->fd,info_begin,SEEK_SET)<0)
-	goto dmg_close;
+	goto fail;
     if(read_uint32(s->fd)!=0x100)
-	goto dmg_close;
+	goto fail;
     if((count = read_uint32(s->fd))==0)
-	goto dmg_close;
+	goto fail;
     info_end = info_begin+count;
     if(lseek(s->fd,0xf8,SEEK_CUR)<0)
-	goto dmg_close;
+	goto fail;
 
     /* read offsets */
     last_in_offset = last_out_offset = 0;
@@ -116,14 +113,14 @@
 
 	count = read_uint32(s->fd);
 	if(count==0)
-	    goto dmg_close;
+	    goto fail;
 	type = read_uint32(s->fd);
 	if(type!=0x6d697368 || count<244)
 	    lseek(s->fd,count-4,SEEK_CUR);
 	else {
 	    int new_size, chunk_count;
 	    if(lseek(s->fd,200,SEEK_CUR)<0)
-	        goto dmg_close;
+	        goto fail;
 	    chunk_count = (count-204)/40;
 	    new_size = sizeof(uint64_t) * (s->n_chunks + chunk_count);
 	    s->types = qemu_realloc(s->types, new_size/2);
@@ -142,7 +139,7 @@
 		    chunk_count--;
 		    i--;
 		    if(lseek(s->fd,36,SEEK_CUR)<0)
-			goto dmg_close;
+			goto fail;
 		    continue;
 		}
 		read_uint32(s->fd);
@@ -163,11 +160,14 @@
     s->compressed_chunk = qemu_malloc(max_compressed_size+1);
     s->uncompressed_chunk = qemu_malloc(512*max_sectors_per_chunk);
     if(inflateInit(&s->zstream) != Z_OK)
-	goto dmg_close;
+	goto fail;
 
     s->current_chunk = s->n_chunks;
 
     return 0;
+fail:
+    close(s->fd);
+    return -1;
 }
 
 static inline int is_sector_in_chunk(BDRVDMGState* s,