Re: [PATCH 1/3] dax: disable filesystem dax on devices that do not map pages

[Jeff Moyer <jmoyer@redhat.com>]

Dan Williams <dan.j.williams@intel.com> writes:

> If a dax buffer from a device that does not map pages is passed to
> read(2) or write(2) as a target for direct-I/O it triggers SIGBUS. If
> gdb attempts to examine the contents of a dax buffer from a device that
> does not map pages it triggers SIGBUS. If fork(2) is called on a process
> with a dax mapping from a device that does not map pages it triggers
> SIGBUS. 'struct page' is required otherwise several kernel code paths
> break in surprising ways. Disable filesystem-dax on devices that do not
> map pages.
>
[...]
> @@ -123,6 +124,12 @@ int __bdev_dax_supported(struct super_block *sb, int blocksize)
>  		return len < 0 ? len : -EIO;
>  	}
>  
> +	if (!pfn_t_has_page(pfn)) {
> +		pr_err("VFS (%s): error: dax support not enabled\n",
> +				sb->s_id);

Is the pr_err really necessary?  At least one caller already prints a
warning.  It seems cleaner to me to let the caller determine whether
it's worth printing anything.

-Jeff

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