Re: [Qemu-devel] [v2 Patch 2/9]block: raw-posix image file reopen

[Supriya Kannery <supriyak@linux.vnet.ibm.com>]

On 08/10/2012 07:15 PM, Corey Bryant wrote:
> 
> 
> On 07/30/2012 05:34 PM, Supriya Kannery wrote:

>> +static int raw_reopen_prepare(BlockDriverState *bs, BDRVReopenState 
>> **prs,
>> + int flags)
>> +{
>> + BDRVRawReopenState *raw_rs = g_malloc0(sizeof(BDRVRawReopenState));
>> + BDRVRawState *s = bs->opaque;
>> + int ret = 0;
>> +
>> + raw_rs->reopen_state.bs = bs;
>> +
>> + /* stash state before reopen */
>> + raw_rs->stash_s = g_malloc0(sizeof(BDRVRawState));
>> + raw_stash_state(raw_rs->stash_s, s);
>> + s->fd = dup3(raw_rs->stash_s->fd, s->fd, O_CLOEXEC);
>> +
>> + *prs = &(raw_rs->reopen_state);
>> +
>> + /* Flags that can be set using fcntl */
>> + int fcntl_flags = BDRV_O_NOCACHE;
>> +
>> + if ((bs->open_flags & ~fcntl_flags) == (flags & ~fcntl_flags)) {
>> + if ((flags & BDRV_O_NOCACHE)) {
>> + s->open_flags |= O_DIRECT;
>> + } else {
>> + s->open_flags &= ~O_DIRECT;
>> + }
>> + ret = fcntl_setfl(s->fd, s->open_flags);
>> + } else {
>> +
>> + /* close and reopen using new flags */
>> + bs->drv->bdrv_close(bs);
>> + ret = bs->drv->bdrv_file_open(bs, bs->filename, flags);
> 
> Will this allow the fdset refcount to get to zero? I was hoping your 
> patches would prevent that from happening. Perhaps Kevin or Eric can 
> weigh in. qemu_open() increments the refcount for an fdset when an fd 
> from it is used, and qemu_close() decrements it. I think if you were 
> able to perform the open before the close here that refcount wouldn't 
> get to zero.
> 

 Since we are duping the file descriptor before reaching this bdrv_close(),
refcount for fd won't become zero.

- thanks, Supriya