Re: [PATCH v9 2/6] fs, mm: pass fd to ->mmap_validate()

[Dan Williams <dan.j.williams@intel.com>]

On Wed, Oct 11, 2017 at 7:17 PM, Dan Williams <dan.j.williams@intel.com> wrote:
> On Wed, Oct 11, 2017 at 6:28 PM, Dan Williams <dan.j.williams@intel.com> wrote:
>> On Wed, Oct 11, 2017 at 6:21 PM, Al Viro <viro@zeniv.linux.org.uk> wrote:
>>> On Wed, Oct 11, 2017 at 05:47:18PM -0700, Dan Williams wrote:
>>>> The MAP_DIRECT mechanism for mmap intends to use a file lease to prevent
>>>> block map changes while the file is mapped. It requires the fd to setup
>>>> an fasync_struct for signalling lease break events to the lease holder.
>>>
>>> *UGH*
>>>
>>> That looks like one hell of a bad API.  You are not even guaranteed that
>>> descriptor will remain be still open by the time you pass it down to your
>>> helper, nevermind the moment when event actually happens...
>>
>> What am I missing, fcntl(F_SETLEASE) seems to follow a similar pattern?
>
> Ugh, so I think the difference with F_SETLEASE is that the lease ends
> when the fd is closed. In the mmap case the lease follows the lifetime
> of the vma. I'll rethink this interface...

I'm not seeing a lot of good options outside of documenting that if
you close the fd that is registered with MAP_DIRECT you may still get
SIGIO notifications with si_fd set to the stale fd.
_______________________________________________
Linux-nvdimm mailing list
Linux-nvdimm@lists.01.org
https://lists.01.org/mailman/listinfo/linux-nvdimm