Re: [PATCH 06/39] vfs: add f_op->pre_mmap()

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On Wed, Jun 6, 2018 at 10:47 PM, Miklos Szeredi <miklos@xxxxxxxxxx> wrote:
> On Wed, Jun 6, 2018 at 8:52 PM, Amir Goldstein <amir73il@xxxxxxxxx> wrote:
>> On Tue, Jun 5, 2018 at 2:36 PM, Miklos Szeredi <miklos@xxxxxxxxxx> wrote:
>>> On Mon, Jun 4, 2018 at 10:48 AM, Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote:
>>>> On Tue, May 29, 2018 at 04:43:06PM +0200, Miklos Szeredi wrote:
>>>>> This is needed by overlayfs to be able to copy up a file from a read-only
>>>>> lower layer to a writable layer when being mapped shared.  When copying up,
>>>>> overlayfs takes VFS locks that would violate locking order when nested
>>>>> inside mmap_sem.
>>>>>
>>>>> Add a new f_op->pre_mmap method, which is called before taking mmap_sem.
>>>>
>>>> NAK.  We really should not add multiple methods for mmap, and everytime
>>>> this came up we found a better way to solve the problem instead.  Most
>>>> recent example was the socket zero copy receive code.
>>>
>>> Okay, I'll drop this.
>>
>> Need to remove copy_up_shared from overlayfs.txt.
>
> Right.  If the pull goes trough in this cycle, I'll send a followup
> patch to fix that.
>

Reminder: stale doc is still in current overlayfs-next.

Thanks,
Amir.
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