Re: [PATCH -V14 0/11] Generic name to handle and open by handlesyscalls

[Miklos Szeredi]

On Wed, 7 Jul 2010, J. Bruce Fields wrote:
> > > If you use sys or proc, is it possible to get the uuid from a file
> > > descriptor or pathname without races?
> > 
> > You can do stat/fstat to find out the device number (which is unique,
> > but not persistent)
> 
> Is it really unique over time? (Can't a given st_dev value map to one
> filesystem now, and another later?) 

It's unique at a single point in time.  But if you have a reference
(e.g. open file descriptor) on the mount then that's not a problem.

   fd = open(path, ...);
   fstat(fd, &st);
   search st.st_dev in mountinfo
   close(fd)

is effectively the same as an getuuid(path) syscall (lazy unmounted
filesystems will not be found in mountinfo, but the reference is still
there so st_dev will not be reused for other filesystems).

Thanks,
Miklos
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