On Wed, 12/03 09:21, Markus Armbruster wrote:
> Fam Zheng <f...@redhat.com> writes:
>
> > Zeroing a buffer that will be filled right after is not necessary, and
> > allocating a power of two + 1 is naughty.
> >
> > Suggested-by: Markus Armbruster <arm...@redhat.com>
> > Signed-off-by: Fam Zheng <f...@redhat.com>
> > ---
> > block/vmdk.c | 5 +++--
> > 1 file changed, 3 insertions(+), 2 deletions(-)
> >
> > diff --git a/block/vmdk.c b/block/vmdk.c
> > index 28d22db..e863a09 100644
> > --- a/block/vmdk.c
> > +++ b/block/vmdk.c
> > @@ -558,14 +558,15 @@ static char *vmdk_read_desc(BlockDriverState *file,
> > uint64_t desc_offset,
> > }
> >
> size = bdrv_getlength(file);
> if (size < 0) {
> error_setg_errno(errp, -size, "Could not access file");
> return NULL;
> }
>
> > size = MIN(size, 1 << 20); /* avoid unbounded allocation */
>
> Consider the case where size <= 1 << 20, i.e. this line is a no-op.
>
> > - buf = g_malloc0(size + 1);
> > + buf = g_malloc(size);
> >
> > - ret = bdrv_pread(file, desc_offset, buf, size);
> > + ret = bdrv_pread(file, desc_offset, buf, size - 1);
>
> Then this reads everything except the last byte (thanks to Don for
> spotting it).
Yes, I was wrong.
>
> > if (ret < 0) {
> > error_setg_errno(errp, -ret, "Could not read from file");
> > g_free(buf);
> > return NULL;
> > }
> > + buf[ret] = 0;
> >
> > return buf;
> > }
>
> I figure Don suggested this instead:
Yes. Thanks.
Fam
>
> diff --git a/block/vmdk.c b/block/vmdk.c
> index 2cbfd3e..b7feb15 100644
> --- a/block/vmdk.c
> +++ b/block/vmdk.c
> @@ -556,8 +556,8 @@ static char *vmdk_read_desc(BlockDriverState *file,
> uint64_t desc_offset,
> return NULL;
> }
>
> - size = MIN(size, 1 << 20); /* avoid unbounded allocation */
> - buf = g_malloc0(size + 1);
> + size = MIN(size, (1 << 20) - 1); /* avoid unbounded allocation */
> + buf = g_malloc(size + 1);
>
> ret = bdrv_pread(file, desc_offset, buf, size);
> if (ret < 0) {
> @@ -565,6 +565,7 @@ static char *vmdk_read_desc(BlockDriverState *file,
> uint64_t desc_offset,
> g_free(buf);
> return NULL;
> }
> + buf[ret] = 0;
>
> return buf;
> }
