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

[Chao Yu]

On 2021/6/4 13:38, Jaegeuk Kim wrote:
> On 06/03, Eric Biggers wrote:
> > On Thu, Jun 03, 2021 at 09:45:25PM -0700, Jaegeuk Kim wrote:
> > > On 06/03, Eric Biggers wrote:
> > > > 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@xxxxxxxxxxxxxxx # v5.11+
> > > > > Signed-off-by: Daniel Rosenberg <drosen@xxxxxxxxxx>
> > > > > ---
> > > > >   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");
> > > > > @@ -579,6 +582,7 @@ enum feat_id {
> > > > >   	FEAT_CASEFOLD,
> > > > >   	FEAT_COMPRESSION,
> > > > >   	FEAT_TEST_DUMMY_ENCRYPTION_V2,
> > > > > +	FEAT_ENCRYPTED_CASEFOLD,
> > > > >   };
> > > >
> > > > Actually looking at it more closely, this patch is wrong.
> > > >
> > > > It only makes sense to declare "encrypted_casefold" as a feature of the
> > > > filesystem implementation, i.e. /sys/fs/f2fs/features/encrypted_casefold.
> > > >
> > > > It does *not* make sense to declare it as a feature of a particular filesystem
> > > > instance, i.e. /sys/fs/f2fs/$disk/features, as it is already implied by the
> > > > filesystem instance having both the encryption and casefold features enabled.
> > > >
> > > > Can we add /sys/fs/f2fs/features/encrypted_casefold only?
> > >
> > > wait.. /sys/fs/f2fs/features/encrypted_casefold is on by
> > > CONFIG_FS_ENCRYPTION && CONFIG_UNICODE.
> > > OTOH, /sys/fs/f2fs/$dis/feature_list/encrypted_casefold is on by
> > > on-disk features: F2FS_FEATURE_ENCRYPT and F2FS_FEATURE_CASEFOLD.
> >
> > Yes, but in the on-disk case, encrypted_casefold is redundant because it simply
> > means encrypt && casefold.  There is no encrypted_casefold flag on-disk.
>
> I prefer to keep encrypted_casefold likewise kernel feature, which is more
> intuitive to users.

encrypted_casefold is a kernel feature support flag, not a disk one, IMO, it's
not needed to add it in to per-disk feature list, it may mislead user that
compatible encrypted casefold needs a extra disk layout support while disk has
already encrypted and casefold feature enabled.

Thanks,

> > - Eric