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Date:   Tue, 27 Apr 2021 17:33:12 +0200
From:   Fabio Aiuto <fabioaiuto83@gmail.com>
To:     Alex Gaynor <alex.gaynor@gmail.com>
Cc:     rust-for-linux <rust-for-linux@vger.kernel.org>
Subject: Re: Question on Box<T> smart pointer
Message-ID: <20210427153311.GB4653@agape.jhs>
References: <20210427152015.GA4653@agape.jhs>
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On Tue, Apr 27, 2021 at 11:22:23AM -0400, Alex Gaynor wrote:
> Box<T> in the kernel allocates on the kernel heap, via kmalloc. This
> is done by providing a Rust GlobalAllocator:
> https://github.com/Rust-for-Linux/linux/blob/rust/rust/kernel/allocator.rs#L11

so this code:

pub struct KernelAllocator;

unsafe impl GlobalAlloc for KernelAllocator {
    unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
        // `krealloc()` is used instead of `kmalloc()` because the latter is
        // an inline function and cannot be bound to as a result.
        bindings::krealloc(ptr::null(), layout.size(), bindings::GFP_KERNEL) as *mut u8
    }

    unsafe fn dealloc(&self, ptr: *mut u8, _layout: Layout) {
        bindings::kfree(ptr as *const c_types::c_void);
    }
}

overrides the default behaviour of Box<T> defined
in core::alloc::GlobalAlloc, doesn't it?

So this code overrides the general heap allocation
facility, not just Box<T>, right?

thank you,

fabio

> 
> Alex
> 
> On Tue, Apr 27, 2021 at 11:20 AM Fabio Aiuto <fabioaiuto83@gmail.com> wrote:
> >
> > Hi all,
> >
> > I have a question. There's one thing I miss.
> >
> > If Box<T> smart pointer allows allocating space on the heap,
> > how is this behaviour overridden in linux kernel Rust?
> >
> > I mean, in c we have all API's to allocate heap space,
> > but using "pure" Box<T> in kernel space what kind of
> > allocation provides?
> >
> > If this question is stupid I apologize in advance,
> >
> > thank you,
> >
> > fabio
> 
> 
> 
> -- 
> All that is necessary for evil to succeed is for good people to do nothing.