linux-kernel - Re: [PATCH v13 15/35] fs: Export anon_inode_getfile

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Message-ID: <e39a8f6e-c98d-4873-aa3f-2e566dead5c5@redhat.com>
Date:   Fri, 3 Nov 2023 11:40:56 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Christian Brauner <brauner@...nel.org>,
        Sean Christopherson <seanjc@...gle.com>
Cc:     Marc Zyngier <maz@...nel.org>,
        Oliver Upton <oliver.upton@...ux.dev>,
        Huacai Chen <chenhuacai@...nel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Anup Patel <anup@...infault.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>, kvm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
        linux-mips@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        kvm-riscv@...ts.infradead.org, linux-riscv@...ts.infradead.org,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Xiaoyao Li <xiaoyao.li@...el.com>,
        Xu Yilun <yilun.xu@...el.com>,
        Chao Peng <chao.p.peng@...ux.intel.com>,
        Fuad Tabba <tabba@...gle.com>,
        Jarkko Sakkinen <jarkko@...nel.org>,
        Anish Moorthy <amoorthy@...gle.com>,
        David Matlack <dmatlack@...gle.com>,
        Yu Zhang <yu.c.zhang@...ux.intel.com>,
        Isaku Yamahata <isaku.yamahata@...el.com>,
        Mickaël Salaün <mic@...ikod.net>,
        Vlastimil Babka <vbabka@...e.cz>,
        Vishal Annapurve <vannapurve@...gle.com>,
        Ackerley Tng <ackerleytng@...gle.com>,
        Maciej Szmigiero <mail@...iej.szmigiero.name>,
        David Hildenbrand <david@...hat.com>,
        Quentin Perret <qperret@...gle.com>,
        Michael Roth <michael.roth@....com>,
        Wang <wei.w.wang@...el.com>,
        Liam Merwick <liam.merwick@...cle.com>,
        Isaku Yamahata <isaku.yamahata@...il.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [PATCH v13 15/35] fs: Export anon_inode_getfile_secure() for use
 by KVM

On 11/2/23 17:24, Christian Brauner wrote:
> On Fri, Oct 27, 2023 at 11:21:57AM -0700, Sean Christopherson wrote:
>> Export anon_inode_getfile_secure() so that it can be used by KVM to create
>> and manage file-based guest memory without need a fullblow filesystem.
>> The "standard" anon_inode_getfd() doesn't work for KVM's use case as KVM
>> needs a unique inode for each file, e.g. to be able to independently
>> manage the size and lifecycle of a given file.
>>
>> Note, KVM doesn't need a "secure" version, just unique inodes, i.e. ignore
>> the name.
>>
>> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
>> ---
> 
> Before we enshrine this misleading name let's rename this to:
> 
> create_anon_inode_getfile()
> 
> I don't claim it's a great name but it's better than *_secure() which is
> very confusing. So just:
> 
> struct file *create_anon_inode_getfile(const char *name,
>                                         const struct file_operations *fops,
>                                         void *priv, int flags)

I slightly prefer anon_inode_create_getfile(); grepping include/linux 
for '\<create_' vs '_create_' shows that this is much more common.

Neither userfaultfd (which uses anon_inode_getfd_secure()) nor io_uring 
strictly speaking need separate inodes; they do want the call to 
inode_init_security_anon().  But I agree that the new name is better and 
I will adjust the comments so that it is clear why you'd use this 
function instead of anon_inode_get{file,fd}().

> May also just remove that context_inode argument from the exported
> function. The only other caller is io_uring. And neither it nor this
> patchset need the context_inode thing afaict.

True, OTOH we might as well rename anon_inode_getfd_secure() to 
anon_inode_create_getfd(), and that one does need context_inode.

I'll Cc you on v14 and will carry the patch in my tree.

Paolo

> Merge conflict risk is
> extremely low so carrying that as part of this patchset is fine and
> shouldn't cause huge issues for you.
>