[PATCH v2] erofs: Fallback to normal access if DAX is not supported on extra device

[Hongbo Li]

Hi Yuezhang,

On 2025/7/28 12:54, Yuezhang Mo wrote:
> If using multiple devices, we should check if the extra device support
> DAX instead of checking the primary device when deciding if to use DAX
> to access a file.
> 
> If an extra device does not support DAX we should fallback to normal
> access otherwise the data on that device will be inaccessible.
> 
> Signed-off-by: Yuezhang Mo <Yuezhang.Mo at sony.com>
> Reviewed-by: Friendy Su <friendy.su at sony.com>
> Reviewed-by: Jacky Cao <jacky.cao at sony.com>
> Reviewed-by: Daniel Palmer <daniel.palmer at sony.com>
> ---
>   fs/erofs/super.c | 24 ++++++++++++++----------
>   1 file changed, 14 insertions(+), 10 deletions(-)
> 
> diff --git a/fs/erofs/super.c b/fs/erofs/super.c
> index e1020aa60771..b08016bf9d1e 100644
> --- a/fs/erofs/super.c
> +++ b/fs/erofs/super.c
> @@ -174,6 +174,11 @@ static int erofs_init_device(struct erofs_buf *buf, struct super_block *sb,
>   		if (!erofs_is_fileio_mode(sbi)) {
>   			dif->dax_dev = fs_dax_get_by_bdev(file_bdev(file),
>   					&dif->dax_part_off, NULL, NULL);
> +			if (!dif->dax_dev && test_opt(&sbi->opt, DAX_ALWAYS)) {
> +				erofs_info(sb, "DAX unsupported by %s. Turning off DAX.",
> +					   dif->path);
> +				clear_opt(&sbi->opt, DAX_ALWAYS);
> +			}
>   		} else if (!S_ISREG(file_inode(file)->i_mode)) {
>   			fput(file);
>   			return -EINVAL;
> @@ -210,8 +215,13 @@ static int erofs_scan_devices(struct super_block *sb,
>   			  ondisk_extradevs, sbi->devs->extra_devices);
>   		return -EINVAL;
>   	}
> -	if (!ondisk_extradevs)
> +	if (!ondisk_extradevs) {
> +		if (test_opt(&sbi->opt, DAX_ALWAYS) && !sbi->dif0.dax_dev) {
> +			erofs_info(sb, "DAX unsupported by block device. Turning off DAX.");
> +			clear_opt(&sbi->opt, DAX_ALWAYS);
> +		}
>   		return 0;
> +	}
>   
>   	if (!sbi->devs->extra_devices && !erofs_is_fscache_mode(sb))
>   		sbi->devs->flatdev = true;
> @@ -338,7 +348,6 @@ static int erofs_read_superblock(struct super_block *sb)
>   	if (ret < 0)
>   		goto out;
>   
> -	/* handle multiple devices */
>   	ret = erofs_scan_devices(sb, dsb);
>   
>   	if (erofs_sb_has_48bit(sbi))
> @@ -671,14 +680,9 @@ static int erofs_fc_fill_super(struct super_block *sb, struct fs_context *fc)
>   			return invalfc(fc, "cannot use fsoffset in fscache mode");
>   	}
>   
> -	if (test_opt(&sbi->opt, DAX_ALWAYS)) {
> -		if (!sbi->dif0.dax_dev) {
> -			errorfc(fc, "DAX unsupported by block device. Turning off DAX.");
> -			clear_opt(&sbi->opt, DAX_ALWAYS);
> -		} else if (sbi->blkszbits != PAGE_SHIFT) {
> -			errorfc(fc, "unsupported blocksize for DAX");
> -			clear_opt(&sbi->opt, DAX_ALWAYS);
> -		}
> +	if (test_opt(&sbi->opt, DAX_ALWAYS) && sbi->blkszbits != PAGE_SHIFT) {
> +		errorfc(fc, "unsupported blocksize for DAX");

How about using the info log? Can we consider using infofc in this case?

Thanks,
Hongbo

> +		clear_opt(&sbi->opt, DAX_ALWAYS);
>   	}
>   
>   	sb->s_time_gran = 1;