Re: [PATCH 0/9] More truncate improvements

[Eric Blake <eblake@redhat.com>]

On 4/28/20 9:24 PM, no-reply@patchew.org wrote:
> Patchew URL: https://patchew.org/QEMU/20200428202905.770727-1-eblake@redhat.com/
> 

> /tmp/qemu-test/src/block/parallels.c: In function 'parallels_co_writev':
> /tmp/qemu-test/src/block/parallels.c:218:12: error: 'ret' may be used uninitialized in this function [-Werror=maybe-uninitialized]
>           if (ret < 0) {
>              ^
> /tmp/qemu-test/src/block/parallels.c:169:9: note: 'ret' was declared here
>       int ret;
>           ^

False positive: the code is roughly:

int ret;
if (cond1) {
   ret = ...;
}
if (cond2) {
   ret = ...;
}
if (ret < 0)

but the compiler can't prove that cond1 + cond2 covers all 
possibilities.  The obvious fix is to initialize ret; squash this into 7/9:

diff --git i/block/parallels.c w/block/parallels.c
index eb6c6c01b998..e7717c508e62 100644
--- i/block/parallels.c
+++ w/block/parallels.c
@@ -166,7 +166,7 @@ static int64_t block_status(BDRVParallelsState *s, 
int64_t sector_num,
  static int64_t allocate_clusters(BlockDriverState *bs, int64_t sector_num,
                                   int nb_sectors, int *pnum)
  {
-    int ret;
+    int ret = 0;
      BDRVParallelsState *s = bs->opaque;
      int64_t pos, space, idx, to_allocate, i, len;





-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org