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Re: [Qemu-block] [PATCH] block, migration: Use qemu_madvise inplace of m

From: Pankaj Gupta
Subject: Re: [Qemu-block] [PATCH] block, migration: Use qemu_madvise inplace of madvise
Date: Fri, 17 Feb 2017 06:30:28 -0500 (EST)

Thanks for your comments. I have below query.
> On Fri 17 Feb 2017 09:06:04 AM CET, Pankaj Gupta wrote:
> >  To maintain consistency at all the places use qemu_madvise wrapper
> >  inplace of madvise call.
> >      if (length > 0) {
> > -        madvise((uint8_t *) t + offset, length, MADV_DONTNEED);
> > +        qemu_madvise((uint8_t *) t + offset, length, QEMU_MADV_DONTNEED);
> This was changed two months ago from qemu_madvise() to madvise(), is
> there any reason why you want to revert that change? Those two calls are
> not equivalent, please see commit 2f2c8d6b371cfc6689affb0b7e for an
> explanation.
> > -    if (madvise(start, length, MADV_DONTNEED)) {
> > +    if (qemu_madvise(start, length, QEMU_MADV_DONTNEED)) {
> >          error_report("%s MADV_DONTNEED: %s", __func__, strerror(errno));

I checked history of only change related to 'postcopy'.

For my linux machine:



As both these options are set for Linux, every time we call call 'qemu_madvise' 
==>"madvise(addr, len, advice);" will 
be compiled/called. I don't understand why '2f2c8d6b371cfc6689affb0b7e' 
explicitly changed for :"#ifdef CONFIG_LINUX"
I think its better to write generic function maybe in a wrapper then to 
conditionally set something at different places.

int qemu_madvise(void *addr, size_t len, int advice)
    if (advice == QEMU_MADV_INVALID) {
        errno = EINVAL;
        return -1;
#if defined(CONFIG_MADVISE)
    return madvise(addr, len, advice);
    return posix_madvise(addr, len, advice);
    errno = EINVAL;
    return -1;

> And this is the same case.
> Berto

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