linux-kernel - Re: [PATCH v2 2/2] f2fs: Advertise encrypted casefolding in sysfs

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Date:   Thu, 3 Jun 2021 12:04:57 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Daniel Rosenberg <drosen@...gle.com>
Cc:     Jaegeuk Kim <jaegeuk@...nel.org>, Chao Yu <chao@...nel.org>,
        linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        Gabriel Krisman Bertazi <krisman@...labora.com>,
        kernel-team@...roid.com, stable@...r.kernel.org
Subject: Re: [PATCH v2 2/2] f2fs: Advertise encrypted casefolding in sysfs

On Thu, Jun 03, 2021 at 09:50:38AM +0000, Daniel Rosenberg wrote:
> Older kernels don't support encryption with casefolding. This adds
> the sysfs entry encrypted_casefold to show support for those combined
> features. Support for this feature was originally added by
> commit 7ad08a58bf67 ("f2fs: Handle casefolding with Encryption")
> 
> Fixes: 7ad08a58bf67 ("f2fs: Handle casefolding with Encryption")
> Cc: stable@...r.kernel.org # v5.11+
> Signed-off-by: Daniel Rosenberg <drosen@...gle.com>
> ---
>  fs/f2fs/sysfs.c | 15 +++++++++++++--
>  1 file changed, 13 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/f2fs/sysfs.c b/fs/f2fs/sysfs.c
> index 09e3f258eb52..6604291a3cdf 100644
> --- a/fs/f2fs/sysfs.c
> +++ b/fs/f2fs/sysfs.c
> @@ -161,6 +161,9 @@ static ssize_t features_show(struct f2fs_attr *a,
>  	if (f2fs_sb_has_compression(sbi))
>  		len += scnprintf(buf + len, PAGE_SIZE - len, "%s%s",
>  				len ? ", " : "", "compression");
> +	if (f2fs_sb_has_casefold(sbi) && f2fs_sb_has_encrypt(sbi))
> +		len += scnprintf(buf + len, PAGE_SIZE - len, "%s%s",
> +				len ? ", " : "", "encrypted_casefold");
>  	len += scnprintf(buf + len, PAGE_SIZE - len, "%s%s",
>  				len ? ", " : "", "pin_file");
>  	len += scnprintf(buf + len, PAGE_SIZE - len, "\n");

This is a HUGE abuse of sysfs and should not be encouraged and added to.

Please make these "one value per file" and do not keep growing a single
file that has to be parsed otherwise you will break userspace tools.

And I don't see a Documentation/ABI/ entry for this either :(

not good...

greg k-h