Re: [Qemu-devel] [PATCH] block: update string sizes for filename, backing_file, exact_filename

[John Snow]

On 01/13/2015 12:03 PM, Jeff Cody wrote:
The string field entries 'filename', 'backing_file', and
'exact_filename' in the BlockDriverState struct are defined as 1024
bytes.

However, most places that use these values accept a maximum of PATH_MAX
bytes.  This patch makes the BlockDriverStruct field string sizes match
the most common usage.

This patch also updates two block drivers that still use 1024-byte sized
arrays for 'backing_file'.

Signed-off-by: Jeff Cody <jc...@redhat.com>
---
  block/mirror.c            | 2 +-
  block/qapi.c              | 2 +-
  include/block/block_int.h | 8 ++++----
  3 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/block/mirror.c b/block/mirror.c
index 9019d1b..57154eb 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -378,7 +378,7 @@ static void coroutine_fn mirror_run(void *opaque)
      int64_t sector_num, end, sectors_per_chunk, length;
      uint64_t last_pause_ns;
      BlockDriverInfo bdi;
-    char backing_filename[1024];
+    char backing_filename[PATH_MAX];
      int ret = 0;
      int n;

diff --git a/block/qapi.c b/block/qapi.c
index a6fd6f7..c097238 100644
--- a/block/qapi.c
+++ b/block/qapi.c
@@ -175,7 +175,7 @@ void bdrv_query_image_info(BlockDriverState *bs,
  {
      int64_t size;
      const char *backing_filename;
-    char backing_filename2[1024];
+    char backing_filename2[PATH_MAX];
      BlockDriverInfo bdi;
      int ret;
      Error *err = NULL;
diff --git a/include/block/block_int.h b/include/block/block_int.h
index 06a21dd..e264be9 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -339,13 +339,13 @@ struct BlockDriverState {
       * regarding this BDS's context */
      QLIST_HEAD(, BdrvAioNotifier) aio_notifiers;

-    char filename[1024];
-    char backing_file[1024]; /* if non zero, the image is a diff of
-                                this file image */
+    char filename[PATH_MAX];
+    char backing_file[PATH_MAX]; /* if non zero, the image is a diff of
+                                    this file image */
      char backing_format[16]; /* if non-zero and backing_file exists */

      QDict *full_open_options;
-    char exact_filename[1024];
+    char exact_filename[PATH_MAX];

      BlockDriverState *backing_hd;
      BlockDriverState *file;


Is it important that qcow2_open seems to enforce a 1023-char length 
backing_file name?

From qcow2.c, qcow2_open (currently line ~871):
        if (len > MIN(1023, s->cluster_size - 
header.backing_file_offset)) {