[Qemu-devel] [PATCH V6 1/5] block/qemu-img: Refine and export infinite loop checking in collect_image_info_list()

[Xu Wang]

If there is a loop in the backing file chain, it could cause problems
such as no response or a segfault during system boot. Hence detecting a
backing file loop is necessary. This patch extracts the loop check from
collect_image_info_list() in block.c into independent functions
bdrv_backing_chain_okay() and bdrv_image_create_okay().

Signed-off-by: Xu Wang <address@hidden>
---
 block.c               | 117 ++++++++++++++++++++++++++++++++++++++++++++++++++
 include/block/block.h |   4 ++
 qemu-img.c            |  44 ++++++++-----------
 3 files changed, 139 insertions(+), 26 deletions(-)

diff --git a/block.c b/block.c
index 58efb5b..3443117 100644
--- a/block.c
+++ b/block.c
@@ -4490,6 +4490,123 @@ bdrv_acct_done(BlockDriverState *bs, BlockAcctCookie 
*cookie)
     bs->total_time_ns[cookie->type] += get_clock() - cookie->start_time_ns;
 }
 
+static gboolean str_equal_func(gconstpointer a, gconstpointer b)
+{
+    return strcmp(a, b) == 0;
+}
+
+static bool file_chain_loop_check(GHashTable *filenames, const char *filename,
+                                  const char *fmt) {
+    BlockDriverState *bs;
+    BlockDriver *drv;
+    char fbuf[1024];
+    int ret;
+    Error *local_err = NULL;
+
+    while (filename && (filename[0] != '\0')) {
+        if (g_hash_table_lookup_extended(filenames, filename, NULL, NULL)) {
+            error_report("Backing file '%s' creates an infinite loop.",
+                         filename);
+            return true;
+        }
+        g_hash_table_insert(filenames, (gpointer)filename, NULL);
+
+        bs = bdrv_new("image");
+
+        if (fmt) {
+            drv = bdrv_find_format(fmt);
+            if (!drv) {
+                error_report("Unknown file format '%s'", fmt);
+                bdrv_delete(bs);
+                return true;
+            }
+        } else {
+            drv = NULL;
+        }
+
+        ret = bdrv_open(bs, filename, NULL,
+                        BDRV_O_CACHE_WB | BDRV_O_NO_BACKING, drv, &local_err);
+        if (ret < 0) {
+            error_report("Could not open '%s': %s", filename,
+                         error_get_pretty(local_err));
+            error_free(local_err);
+            local_err = NULL;
+            return true;
+        }
+
+        bdrv_get_backing_filename(bs, fbuf, sizeof(fbuf));
+        filename = fbuf;
+        fmt = NULL;
+
+        bdrv_unref(bs);
+    }
+
+    return false;
+}
+
+/**
+ * Check backing file chain if there is a loop in it.
+ *
+ * @filename: topmost image filename of backing file chain.
+ * @fmt: topmost image format of backing file chain(may be NULL to autodetect).
+ *
+ * Returns: true for backing file loop or error happened, false for no loop.
+ */
+bool bdrv_backing_chain_okay(const char *filename, const char *fmt) {
+    GHashTable *filenames;
+
+    if (filename == NULL || filename[0] == '\0') {
+        return true;
+    }
+
+    filenames = g_hash_table_new_full(g_str_hash, str_equal_func, NULL, NULL);
+
+    if (file_chain_loop_check(filenames, filename, fmt)) {
+        goto err;
+    }
+
+    g_hash_table_destroy(filenames);
+    return true;
+
+err:
+    g_hash_table_destroy(filenames);
+    return false;
+}
+
+/**
+ * Check if there is loop exists in the backing file chain and if there will
+ * be loop occur after backing file chain updated or new image created.
+ *
+ * @filename: the image filename to be created.
+ * @backing_file: topmost image filename of backing file chain.
+ * @backing_fmt: topmost image format (may be NULL to autodetect).
+ *
+ * Returns: true for backing file loop or error happened, false for no loop.
+ */
+bool bdrv_new_chain_okay(const char *filename, const char *backing_file,
+                          const char *backing_fmt) {
+    GHashTable *filenames;
+
+    if (backing_file == NULL || backing_file[0] == '\0') {
+        return true;
+    }
+
+    filenames = g_hash_table_new_full(g_str_hash, str_equal_func, NULL, NULL);
+
+    g_hash_table_insert(filenames, (gpointer)filename, NULL);
+
+    if (file_chain_loop_check(filenames, backing_file, backing_fmt)) {
+        goto err;
+    }
+
+    g_hash_table_destroy(filenames);
+    return true;
+
+err:
+    g_hash_table_destroy(filenames);
+    return false;
+}
+
 void bdrv_img_create(const char *filename, const char *fmt,
                      const char *base_filename, const char *base_fmt,
                      char *options, uint64_t img_size, int flags,
diff --git a/include/block/block.h b/include/block/block.h
index 3560deb..0945c09 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -378,6 +378,10 @@ int bdrv_save_vmstate(BlockDriverState *bs, const uint8_t 
*buf,
 int bdrv_load_vmstate(BlockDriverState *bs, uint8_t *buf,
                       int64_t pos, int size);
 
+bool bdrv_backing_chain_okay(const char *filename, const char *fmt);
+bool bdrv_new_chain_okay(const char *filename, const char *backing_file,
+                            const char *backing_fmt);
+
 void bdrv_img_create(const char *filename, const char *fmt,
                      const char *base_filename, const char *base_fmt,
                      char *options, uint64_t img_size, int flags,
diff --git a/qemu-img.c b/qemu-img.c
index bf3fb4f..d5ec45b 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -1641,11 +1641,6 @@ static void dump_human_image_info_list(ImageInfoList 
*list)
     }
 }
 
-static gboolean str_equal_func(gconstpointer a, gconstpointer b)
-{
-    return strcmp(a, b) == 0;
-}
-
 /**
  * Open an image file chain and return an ImageInfoList
  *
@@ -1663,30 +1658,24 @@ static ImageInfoList *collect_image_info_list(const 
char *filename,
                                               bool chain)
 {
     ImageInfoList *head = NULL;
+    BlockDriverState *bs;
+    ImageInfoList *elem;
     ImageInfoList **last = &head;
-    GHashTable *filenames;
+    ImageInfo *info;
     Error *err = NULL;
+    int flags = BDRV_O_FLAGS;
 
-    filenames = g_hash_table_new_full(g_str_hash, str_equal_func, NULL, NULL);
-
-    while (filename) {
-        BlockDriverState *bs;
-        ImageInfo *info;
-        ImageInfoList *elem;
-
-        if (g_hash_table_lookup_extended(filenames, filename, NULL, NULL)) {
-            error_report("Backing file '%s' creates an infinite loop.",
-                         filename);
-            goto err;
-        }
-        g_hash_table_insert(filenames, (gpointer)filename, NULL);
+    if (!chain) {
+        flags |= BDRV_O_NO_BACKING;
+    }
 
-        bs = bdrv_new_open(filename, fmt, BDRV_O_FLAGS | BDRV_O_NO_BACKING,
-                           false, false);
-        if (!bs) {
-            goto err;
-        }
+    bs = bdrv_new_open(filename, fmt, flags,
+                       false, false);
+    if (!bs) {
+        goto err;
+    }
 
+    while (filename) {
         bdrv_query_image_info(bs, &info, &err);
         if (error_is_set(&err)) {
             error_report("%s", error_get_pretty(err));
@@ -1711,14 +1700,17 @@ static ImageInfoList *collect_image_info_list(const 
char *filename,
             if (info->has_backing_filename_format) {
                 fmt = info->backing_filename_format;
             }
+
+            if (filename) {
+                bs = bdrv_find_backing_image(bs, filename);
+            }
         }
     }
-    g_hash_table_destroy(filenames);
+
     return head;
 
 err:
     qapi_free_ImageInfoList(head);
-    g_hash_table_destroy(filenames);
     return NULL;
 }
 
-- 
1.8.1.4