lkml.org 
[lkml]   [2023]   [Jan]   [26]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: [PATCH v11 2/8] iov_iter: Add a function to extract a page list from an iterator
From
On 26.01.23 23:36, Al Viro wrote:
> On Thu, Jan 26, 2023 at 09:59:36PM +0000, Al Viro wrote:
>> On Thu, Jan 26, 2023 at 02:16:20PM +0000, David Howells wrote:
>>
>>> +/**
>>> + * iov_iter_extract_will_pin - Indicate how pages from the iterator will be retained
>>> + * @iter: The iterator
>>> + *
>>> + * Examine the iterator and indicate by returning true or false as to how, if
>>> + * at all, pages extracted from the iterator will be retained by the extraction
>>> + * function.
>>> + *
>>> + * %true indicates that the pages will have a pin placed in them that the
>>> + * caller must unpin. This is must be done for DMA/async DIO to force fork()
>>> + * to forcibly copy a page for the child (the parent must retain the original
>>> + * page).
>>> + *
>>> + * %false indicates that no measures are taken and that it's up to the caller
>>> + * to retain the pages.
>>> + */
>>> +static inline bool iov_iter_extract_will_pin(const struct iov_iter *iter)
>>> +{
>>> + return user_backed_iter(iter);
>>> +}
>>> +
>>
>> Wait a sec; why would we want a pin for pages we won't be modifying?
>> A reference - sure, but...
>
> After having looked through the earlier iterations of the patchset -
> sorry, but that won't fly for (at least) vmsplice(). There we can't
> pin those suckers;

We'll need a way to pass FOLL_LONGTERM to pin_user_pages_fast() to
handle such long-term pinning as vmsplice() needs. But the release path
(unpin) will be the same.

--
Thanks,

David / dhildenb

\
 
 \ /
  Last update: 2023-03-26 23:57    [W:0.094 / U:0.192 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site