[Qemu-devel] [PATCH V2 1/5] Refine and export infinite loop checking in collect_image_info_list()

[Xu Wang]

Signed-off-by: Xu Wang <address@hidden>
---
 block.c               | 101 ++++++++++++++++++++++++++++++++++++++++++++++++++
 include/block/block.h |   4 ++
 qemu-img.c            |  30 +++++----------
 3 files changed, 114 insertions(+), 21 deletions(-)

diff --git a/block.c b/block.c
index b88ad2f..53b1a01 100644
--- a/block.c
+++ b/block.c
@@ -4431,6 +4431,107 @@ 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;
+}
+
+/**
+ * Check backing file chain if there is a loop in it and build list of
+ * ImageInfo if needed.
+ *
+ * @filename: topmost image filename, absolute or relative path is OK.
+ * @fmt: topmost image format (may be NULL to autodetect)
+ * @head: head of ImageInfo list. If not need please set head to null.
+ * @chain: true  - enumerate entire backing file chain
+ *         false - only topmost image file
+ * @backing_file: if this value is set, @filename inode (-1 if it doesn't
+ *                exist) will insert into hash table directly. Loop check
+ *                starts from it. Absolute or relative path is OK for it.
+ * @backing_format: format of backing file
+ *
+ * If return true, stands for a backing file loop exists or some error
+ * happened. If return false, everything is ok.
+ */
+bool bdrv_backing_file_loop_check(const char *filename, const char *fmt,
+                                  bool chain, const char *backing_file,
+                                  const char *backing_format) {
+    GHashTable *inodes;
+    BlockDriverState *bs;
+    BlockDriver *drv;
+    struct stat sbuf;
+    long inode = 0;
+    int ret;
+    char fbuf[1024];
+
+    inodes = g_hash_table_new_full(g_str_hash, str_equal_func, NULL, NULL);
+
+    if (backing_file) {
+        /* Check if file exists. */
+        if (access(filename, F_OK)) {
+            inode = -1;
+        } else {
+            if (stat(filename, &sbuf) == -1) {
+                error_report("Get file %s stat failed.", filename);
+                goto err;
+            }
+            inode = (long)sbuf.st_ino;
+        }
+
+        filename = backing_file;
+        fmt = backing_format;
+        g_hash_table_insert(inodes, (gpointer)&inode, NULL);
+    }
+
+    while (filename && (filename[0] != '\0')) {
+        if (stat(filename, &sbuf) == -1) {
+                error_report("Get file %s stat failed.", filename);
+                goto err;
+        }
+        inode = (long)sbuf.st_ino;
+
+        if (g_hash_table_lookup_extended(inodes, &inode, NULL, NULL)) {
+            error_report("Backing file '%s' creates an infinite loop.",
+                         filename);
+            goto err;
+        }
+        g_hash_table_insert(inodes, (gpointer)&inode, NULL);
+
+        bs = bdrv_new("image");
+
+        if (fmt) {
+            drv = bdrv_find_format(fmt);
+            if (!drv) {
+                error_report("Unknown file format '%s'", fmt);
+                goto err;
+            }
+        } else {
+            drv = NULL;
+        }
+
+        ret = bdrv_open(bs, filename, NULL,
+                        BDRV_O_CACHE_WB | BDRV_O_NO_BACKING, drv);
+        if (ret < 0) {
+            error_report("Could not open '%s': %s", filename, strerror(-ret));
+            goto err;
+        }
+
+        filename = fmt = NULL;
+        if (chain) {
+            bdrv_get_backing_filename(bs, fbuf, sizeof(fbuf));
+            filename = fbuf;
+        }
+
+        bdrv_delete(bs);
+    }
+    g_hash_table_destroy(inodes);
+    return false;
+
+err:
+    g_hash_table_destroy(inodes);
+    return true;
+}
+
 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 2307f67..6c631f2 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -332,6 +332,10 @@ 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_file_loop_check(const char *filename, const char *fmt,
+                             bool chain, const char *backing_file,
+                             const char *backing_format);
+
 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 809b4f1..48284c5 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -1620,11 +1620,6 @@ 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
  *
@@ -1642,24 +1637,18 @@ 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;
-
-    filenames = g_hash_table_new_full(g_str_hash, str_equal_func, NULL, NULL);
+        
+    /* check if loop exists and build ImageInfoList */
+    if (bdrv_backing_file_loop_check(filename, fmt, chain, NULL, NULL)) {
+        goto err;
+    }
 
     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);
-
         bs = bdrv_new_open(filename, fmt, BDRV_O_FLAGS | BDRV_O_NO_BACKING,
                            false, false);
         if (!bs) {
@@ -1692,12 +1681,11 @@ static ImageInfoList *collect_image_info_list(const 
char *filename,
             }
         }
     }
-    g_hash_table_destroy(filenames);
+
     return head;
 
 err:
     qapi_free_ImageInfoList(head);
-    g_hash_table_destroy(filenames);
     return NULL;
 }
 
-- 
1.8.1.4