2013/11/20 Stefan Hajnoczi <stefa...@gmail.com>
> On Wed, Nov 20, 2013 at 04:50:29PM +0800, Chunyan Liu wrote:
> > block/cow.c | 22 ++++++++++++++++++++++
> > block/qcow.c | 22 ++++++++++++++++++++++
> > block/qcow2.c | 22 ++++++++++++++++++++++
>
> I think you can avoid modifying all the image formats:
>
> .bdrv_create() functions pass options to bdrv_create_file(). Therefore
> an image format like qcow2 does not need to parse the nocow option
> itself. Only raw-posix.c:.bdrv_create() needs to know about the nocow
> option.
>
>
In existing code, options passed to bdrv_create_file contains no option in
fact.
And if we pass all options to bdrv_create_file directly, raw-posix.c:
.bdrv_create() will get NOCOW option but at the same time get SIZE option,
it
will create a file with total size. For cow/qcow/qcow2, I suppose it's not
expected? In current code, bdrv_create_file will create a zero-sized image
for
cow/qcow/qcow2.
> The exception is the block drivers that currently use open(2) directly
> instead of bdrv_create_file(). These should be converted to use
> bdrv_*() APIs instead of POSIX I/O. Please either convert them or skip
> them (someone will get around to fixing them eventually).
>
> > + if (nocow) {
> > + QEMUOptionParameter list[] = {
> > + {
> > + .name = BLOCK_OPT_NOCOW,
> > + .type = OPT_FLAG,
> > + .value.n = 1,
> > + .help = "No copy-on-write",
> > + .assigned = true
> > + },
> > + { NULL }
> > + };
> > + options = list;
> > + }
>
> This doesn't look safe to me. list[] is now out-of-scope (the compiler
> can reuse the stack space) and options is a dangling pointer.
>
>
