linux-kernel - Re: [PATCH 1/3] mm: introduce new .mmap

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Message-ID: <5a489fa9-b2c0-4a7d-aa0e-5a97381e6b33@redhat.com>
Date: Fri, 9 May 2025 12:51:14 +0200
From: David Hildenbrand <david@...hat.com>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
 "Liam R . Howlett" <Liam.Howlett@...cle.com>,
 Vlastimil Babka <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>,
 Suren Baghdasaryan <surenb@...gle.com>, Michal Hocko <mhocko@...e.com>,
 Jann Horn <jannh@...gle.com>, Pedro Falcato <pfalcato@...e.de>,
 linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-mm@...ck.org, Alexander Viro <viro@...iv.linux.org.uk>,
 Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
 Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH 1/3] mm: introduce new .mmap_prepare() file callback

>>> +
>>> +static inline int __call_mmap_prepare(struct file *file,
>>> +		struct vm_area_desc *desc)
>>> +{
>>> +	return file->f_op->mmap_prepare(desc);
>>> +}
>>
>> Hm, is there a way avoid a copy of the exact same code from fs.h, and
>> essentially test the implementation in fs.h (-> more coverage by using less
>> duplciated stubs?).
> 
> Not really, this kind of copying is sadly part of it because we're
> intentionally isolating vma.c from everything else, and if we try to bring
> in other headers they import yet others and etc. etc. it becomes a
> combinatorial explosion potentially.

I guess what would work is inlining __call_mmap_prepare() -- again, 
rather simple wrapper ... and having file_has_valid_mmap_hooks() + 
call_mmap() reside in vma.c. Hm.

As an alternative, we'd really need some separate header that does not 
allow for any other includes, and is essentially only included in the 
other header files.

Duplicating functions in such a way that they can easily go out of sync 
and are not getting tested is really suboptimal. :(

-- 
Cheers,

David / dhildenb