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

[Kevin Wolf <kwolf@redhat.com>]

Am 31.07.2012 19:17, schrieb Eric Blake:
> On 07/30/2012 03:34 PM, Supriya Kannery wrote:
>> raw-posix driver changes for bdrv_reopen_xx functions to
>> safely reopen image files. Reopening of image files while 
>> changing hostcache dynamically is handled here.
>>
>> Signed-off-by: Supriya Kannery <supriyak@linux.vnet.ibm.com>
>>
>> ---
>> Index: qemu/block/raw.c
>> ===================================================================
> 
>> +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);
> 
> You called it out in your cover letter, but just pointing out that this
> is one of the locations that needs a conditional fallback to
> dup2/qemu_set_cloexec if dup3 and O_CLOEXEC are missing.
> 
> More importantly, though, you want this to be fcntl(F_DUP_CLOEXEC) and
> NOT dup3, so that you are duplicating to the first available fd rather
> than accidentally overwriting whatever s->fd happened to be on entry.
> Also, where is your error checking that you didn't just assign s->fd to
> -1?  It looks like your goal here is to stash a copy of the fd, so that
> on failure you can then pivot over to your copy.

Doesn't Corey's fd passing series introduce a helper function for
F_DUP_CLOEXEC and emulation if it isn't support? Could be reused here then.

Kevin