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

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

On 07/31/2012 10:47 PM, Eric Blake wrote:
> On 07/30/2012 03:34 PM, Supriya Kannery wrote:
>> +    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.
> 
 
Will use fcntl(F_DUP_CLOEXEC) in updated patch.
 
>> +
>> +    *prs =&(raw_rs->reopen_state);
>> +
>> +    /* Flags that can be set using fcntl */
>> +    int fcntl_flags = BDRV_O_NOCACHE;
> 
> This variable name is misleading; fcntl_flags in my mind implies O_* not
> BDRV_O_*, as we are not guaranteed that they are the same values.  Maybe
> bdrv_flags is a better name.  Or are you trying to list the subset of
> BDRV_O flags that can be changed via mapping to the appropriate O_ flag
> during fcntl?
> 

  From the list of flags in bdrv->openflags (BDRV_O*), only few of them can be changed
using fcntl. So to identify those allowed subset, I am using fcntl_flags.

Excerpt from man fcntl for F_SETFL:
            On Linux this command can only  change  the  O_APPEND,  O_ASYNC,
              O_DIRECT, O_NOATIME, and O_NONBLOCK flags.

May be naming it fcntl_supported_flags would be better?

- thanks, Supriya