linux-kernel - Re: [PATCH v3 4/5] ext4: disable map

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Date:   Wed, 9 Jan 2019 09:54:19 -0500 (EST)
From:   Pankaj Gupta <pagupta@...hat.com>
To:     Jan Kara <jack@...e.cz>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        qemu-devel@...gnu.org, linux-nvdimm@...1.01.org,
        linux-fsdevel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        linux-acpi@...r.kernel.org, linux-ext4@...r.kernel.org,
        linux-xfs@...r.kernel.org, stefanha@...hat.com,
        dan j williams <dan.j.williams@...el.com>, riel@...riel.com,
        nilal@...hat.com, kwolf@...hat.com, pbonzini@...hat.com,
        zwisler@...nel.org, vishal l verma <vishal.l.verma@...el.com>,
        dave jiang <dave.jiang@...el.com>, david@...hat.com,
        jmoyer@...hat.com,
        xiaoguangrong eric <xiaoguangrong.eric@...il.com>,
        hch@...radead.org, mst@...hat.com, jasowang@...hat.com,
        lcapitulino@...hat.com, imammedo@...hat.com, eblake@...hat.com,
        willy@...radead.org, tytso@....edu,
        adilger kernel <adilger.kernel@...ger.ca>,
        darrick wong <darrick.wong@...cle.com>, rjw@...ysocki.net
Subject: Re: [PATCH v3 4/5] ext4: disable map_sync for virtio pmem


> 
> On Wed 09-01-19 19:26:05, Pankaj Gupta wrote:
> > Virtio pmem provides asynchronous host page cache flush
> > mechanism. We don't support 'MAP_SYNC' with virtio pmem
> > and ext4.
> > 
> > Signed-off-by: Pankaj Gupta <pagupta@...hat.com>
> ...
> > @@ -371,6 +373,13 @@ static int ext4_file_mmap(struct file *file, struct
> > vm_area_struct *vma)
> >  	if (!IS_DAX(file_inode(file)) && (vma->vm_flags & VM_SYNC))
> >  		return -EOPNOTSUPP;
> >  
> > +	/* We don't support synchronous mappings with guest direct access
> > +	 * and virtio based host page cache flush mechanism.
> > +	 */
> > +	if (IS_DAX(file_inode(file)) && virtio_pmem_host_cache_enabled(dax_dev)
> > +						&& (vma->vm_flags & VM_SYNC))
> > +		return -EOPNOTSUPP;
> > +
> 
> Shouldn't there rather be some generic way of doing this? Having
> virtio_pmem_host_cache_enabled() check in filesystem code just looks like
> filesystem sniffing into details is should not care about... Maybe just
> naming this (or having a wrapper) dax_dev_map_sync_supported()?

Thanks for the feedback.

Just wanted to avoid 'dax' in function name just to differentiate this with real dax.
But yes can add a wrapper: dax_dev_map_sync_supported()

Thanks,
Pankaj