On Wed, 3 Dec 2014 17:20:27 +0800
Fam Zheng <f...@redhat.com> wrote:
> 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:
Correct.
>
> 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;
> > }
>
-d
