Re: [Qemu-block] [Qemu-devel] [PATCH 0/4] block: Avoid copy-on-read assertions

[Eric Blake]

On 09/30/2017 04:19 PM, address@hidden wrote:
> Hi,
> 
> This series failed build test on s390x host. Please find the details below.
> 

> /var/tmp/patchew-tester-tmp-a2p2tpcc/src/block/io.c: In function 
> ‘bdrv_aligned_preadv’:
> /var/tmp/patchew-tester-tmp-a2p2tpcc/src/block/io.c:955:9: error: ‘ret’ may 
> be used uninitialized in this function [-Werror=maybe-uninitialized]
>      int ret;
>          ^~~

Blah - I compiled with -g instead of -O2, which masks this warning in my
setup.

The warning is a false negative (the error message is actually pointing
to a line in bdrv_co_do_copy_on_readv - but the compiler must have
inlined it into bdrv_aligned_preadv) - the function is only ever called
with non-zero bytes, and therefore the 'while (cluster_bytes)' loop will
execute at least once, and ret always gets assigned.  But the compiler
can't see that, so I'll squash this in:

commit a201636c3133827bd632d5fdd9eb1f5df81d0e0e
Author: Eric Blake <address@hidden>
Date:   Sat Sep 30 14:27:51 2017 -0500

    fixup! block: Perform copy-on-read in loop

    Signed-off-by: Eric Blake <address@hidden>

diff --git a/block/io.c b/block/io.c
index 5ef5adc7a7..e7519464bb 100644
--- a/block/io.c
+++ b/block/io.c
@@ -952,7 +952,7 @@ static int coroutine_fn
bdrv_co_do_copy_on_readv(BdrvChild *child,
     int64_t cluster_offset;
     unsigned int cluster_bytes;
     size_t skip_bytes;
-    int ret;
+    int ret = 0;
     int max_transfer = MIN_NON_ZERO(bs->bl.max_transfer,
                                     BDRV_REQUEST_MAX_BYTES);
     unsigned int progress = 0;


-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

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