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

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On Wed, Oct 11, 2017 at 6:28 PM, Dan Williams <dan.j.williams@xxxxxxxxx> wrote:
> On Wed, Oct 11, 2017 at 6:21 PM, Al Viro <viro@xxxxxxxxxxxxxxxxxx> 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...
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