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

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Date:   Wed, 9 Jan 2019 15:42:15 +0100
From:   Jan Kara <jack@...e.cz>
To:     Pankaj Gupta <pagupta@...hat.com>
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, jack@...e.cz, stefanha@...hat.com,
        dan.j.williams@...el.com, riel@...riel.com, nilal@...hat.com,
        kwolf@...hat.com, pbonzini@...hat.com, zwisler@...nel.org,
        vishal.l.verma@...el.com, dave.jiang@...el.com, david@...hat.com,
        jmoyer@...hat.com, 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@...ger.ca, 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()?

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR