[Qemu-devel] [PATCH] Re: snapshot: fixed bdrv_get_full_backing_filename can not get correct full_backing_filename

[Qemu-devel] [PATCH] Re: snapshot: fixed bdrv_get_full_backing_filename can not get correct full_backing_filename

[Jun Li]

Thanks Eric's analysis and review firstly. As not so clear to the application context, so the first patch can not cover symlink scenarios.
In this patch, will check the backing_filename is a symlink or not firstly, then return the full(absolute) path via realpath.
If this patch has something not coverd, please give me more suggestions.
Thx.

Signed-off-by: Jun Li <junmuzi@gmail.com>
---
 block.c | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/block.c b/block.c
index 990a754..8566b75 100644
--- a/block.c
+++ b/block.c
@@ -304,10 +304,26 @@ void path_combine(char *dest, int dest_size,
 
 void bdrv_get_full_backing_filename(BlockDriverState *bs, char *dest, size_t sz)
 {
+    struct stat sb;
+    char *linkname;
+
     if (bs->backing_file[0] == '\0' || path_has_protocol(bs->backing_file)) {
         pstrcpy(dest, sz, bs->backing_file);
     } else {
-        path_combine(dest, sz, bs->filename, bs->backing_file);
+        if (lstat(bs->backing_file, &sb) == -1) {
+            perror("lstat");
+            exit(EXIT_FAILURE);
+        }
+
+        /* Check linkname is a link or not */
+        if (S_ISLNK(sb.st_mode)) {
+            linkname = malloc(sb.st_size + 1);
+            readlink(bs->backing_file, linkname, sb.st_size + 1);
+            linkname[sb.st_size] = '\0';
+            realpath(linkname, dest);
+        } else {
+            realpath(bs->backing_file, dest);
+        }
     }
 }
 
-- 
1.8.3.1