block/qcow.c : return real error code in qcow_open

diff --git a/block/qcow.c b/block/qcow.c
index b16955d..e0d0b88 100644
--- a/block/qcow.c
+++ b/block/qcow.c
@@ -95,11 +95,13 @@  static int qcow_probe(const uint8_t *buf, int buf_size, const char *filename)
 static int qcow_open(BlockDriverState *bs, int flags)
 {
     BDRVQcowState *s = bs->opaque;
-    int len, i, shift;
+    int len, i, shift, ret;
     QCowHeader header;
 
-    if (bdrv_pread(bs->file, 0, &header, sizeof(header)) != sizeof(header))
+    ret = bdrv_pread(bs->file, 0, &header, sizeof(header));
+    if (ret < 0) {
         goto fail;
+    }
     be32_to_cpus(&header.magic);
     be32_to_cpus(&header.version);
     be64_to_cpus(&header.backing_file_offset);
@@ -109,15 +111,31 @@  static int qcow_open(BlockDriverState *bs, int flags)
     be32_to_cpus(&header.crypt_method);
     be64_to_cpus(&header.l1_table_offset);
 
-    if (header.magic != QCOW_MAGIC || header.version != QCOW_VERSION)
+    if (header.magic != QCOW_MAGIC) {
+        ret = -EINVAL;
         goto fail;
-    if (header.size <= 1 || header.cluster_bits < 9)
+    }
+    if (header.version != QCOW_VERSION) {
+        char version[64];
+        snprintf(version, sizeof(version), "QCOW version %d", header.version);
+        qerror_report(QERR_UNKNOWN_BLOCK_FORMAT_FEATURE,
+            bs->device_name, "qcow", version);
+        ret = -ENOTSUP;
         goto fail;
-    if (header.crypt_method > QCOW_CRYPT_AES)
+    }
+
+    if (header.size <= 1 || header.cluster_bits < 9) {
+        ret = -EINVAL;
         goto fail;
+    }
+    if (header.crypt_method > QCOW_CRYPT_AES) {
+        ret = -EINVAL;
+        goto fail;
+    }
     s->crypt_method_header = header.crypt_method;
-    if (s->crypt_method_header)
+    if (s->crypt_method_header) {
         bs->encrypted = 1;
+    }
     s->cluster_bits = header.cluster_bits;
     s->cluster_size = 1 << s->cluster_bits;
     s->cluster_sectors = 1 << (s->cluster_bits - 9);
@@ -132,33 +150,33 @@  static int qcow_open(BlockDriverState *bs, int flags)
 
     s->l1_table_offset = header.l1_table_offset;
     s->l1_table = g_malloc(s->l1_size * sizeof(uint64_t));
-    if (!s->l1_table)
-        goto fail;
-    if (bdrv_pread(bs->file, s->l1_table_offset, s->l1_table, s->l1_size * sizeof(uint64_t)) !=
-        s->l1_size * sizeof(uint64_t))
+
+    ret = bdrv_pread(bs->file, s->l1_table_offset, s->l1_table,
+               s->l1_size * sizeof(uint64_t));
+    if (ret < 0) {
         goto fail;
+    }
+
     for(i = 0;i < s->l1_size; i++) {
         be64_to_cpus(&s->l1_table[i]);
     }
     /* alloc L2 cache */
     s->l2_cache = g_malloc(s->l2_size * L2_CACHE_SIZE * sizeof(uint64_t));
-    if (!s->l2_cache)
-        goto fail;
     s->cluster_cache = g_malloc(s->cluster_size);
-    if (!s->cluster_cache)
-        goto fail;
     s->cluster_data = g_malloc(s->cluster_size);
-    if (!s->cluster_data)
-        goto fail;
     s->cluster_cache_offset = -1;
 
     /* read the backing file name */
     if (header.backing_file_offset != 0) {
         len = header.backing_file_size;
-        if (len > 1023)
+        if (len > 1023) {
             len = 1023;
-        if (bdrv_pread(bs->file, header.backing_file_offset, bs->backing_file, len) != len)
+        }
+        ret = bdrv_pread(bs->file, header.backing_file_offset,
+                   bs->backing_file, len);
+        if (ret < 0) {
             goto fail;
+        }
         bs->backing_file[len] = '\0';
     }
 
@@ -176,7 +194,7 @@  static int qcow_open(BlockDriverState *bs, int flags)
     g_free(s->l2_cache);
     g_free(s->cluster_cache);
     g_free(s->cluster_data);
-    return -1;
+    return ret;
 }
 
 static int qcow_set_key(BlockDriverState *bs, const char *key)