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Re: [PATCH 1/3] ext4: Add alignment check for DAX mount

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On 04/29/2016 11:39 PM, Toshi Kani wrote:
> When a partition is not aligned by 4KB, mount -o dax succeeds,
> but any read/write access to the filesystem fails, except for
> metadata update.
> 
> Add alignment check to ext4_fill_super() when -o dax is specified.
> 
> Reported-by: Micah Parrish <micah.parrish@hpe.com>
> Signed-off-by: Toshi Kani <toshi.kani@hpe.com>
> Cc: "Theodore Ts'o" <tytso@mit.edu>
> Cc: Andreas Dilger <adilger.kernel@dilger.ca>
> Cc: Jan Kara <jack@suse.cz>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
> ---
>  fs/ext4/super.c |    6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index 304c712..90a8670 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -3421,6 +3421,12 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
>  					"error: unsupported blocksize for dax");
>  			goto failed_mount;
>  		}
> +		if (sb->s_bdev->bd_part->start_sect % (PAGE_SIZE / 512) ||
> +		    sb->s_bdev->bd_part->nr_sects % (PAGE_SIZE / 512)) {

Can you please not do this like this? For me is a layering violation only
the device should know what are its limits.

I would prefer if you just try to bdev_direct_access() the 0 sector and if
it fails then fail here. This way you let the device decide what it needs
and if/how to support unaligned partitions.
(For example it could by shrinking its size)

Thanks
Boaz

> +			ext4_msg(sb, KERN_ERR,
> +					"error: unaligned partition for dax");
> +			goto failed_mount;
> +		}
>  		if (!sb->s_bdev->bd_disk->fops->direct_access) {
>  			ext4_msg(sb, KERN_ERR,
>  					"error: device does not support dax");
> _______________________________________________
> Linux-nvdimm mailing list
> Linux-nvdimm@lists.01.org
> https://lists.01.org/mailman/listinfo/linux-nvdimm
> 

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[PATCH 0/3] Add alignment check for DAX mount Toshi Kani <toshi.kani@hpe.com> - 2016-04-29 22:50 +0200
  [PATCH 1/3] ext4: Add alignment check for DAX mount Toshi Kani <toshi.kani@hpe.com> - 2016-04-29 22:50 +0200
    Re: [PATCH 1/3] ext4: Add alignment check for DAX mount Boaz Harrosh <boaz@plexistor.com> - 2016-05-01 11:40 +0200
    Re: [PATCH 1/3] ext4: Add alignment check for DAX mount Christoph Hellwig <hch@infradead.org> - 2016-05-01 19:40 +0200
      Re: [PATCH 1/3] ext4: Add alignment check for DAX mount Boaz Harrosh <boaz@plexistor.com> - 2016-05-02 11:50 +0200
        Re: [PATCH 1/3] ext4: Add alignment check for DAX mount Toshi Kani <toshi.kani@hpe.com> - 2016-05-02 17:40 +0200
  [PATCH 3/3] xfs: Add alignment check for DAX mount Toshi Kani <toshi.kani@hpe.com> - 2016-04-29 22:50 +0200
  Re: [PATCH 0/3] Add alignment check for DAX mount Ross Zwisler <ross.zwisler@linux.intel.com> - 2016-04-30 01:20 +0200

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