On 03/30, Chao Yu wrote:
> Hi Eric,
>
> On 2018/3/29 2:15, Eric Biggers wrote:
> > Reserve an F2FS feature flag and inode flag for fs-verity. This is an
> > in-development feature that is planned be discussed at LSF/MM 2018 [1].
> > It will provide file-based integrity and authenticity for read-only
> > files. Most code will be in a filesystem-independent module, with
> > smaller changes needed to individual filesystems that opt-in to
> > supporting the feature. An early prototype supporting F2FS is available
> > [2]. Reserving the F2FS on-disk bits for fs-verity will prevent users
> > of the prototype from conflicting with other new F2FS features.
> >
> > Note that we're reserving the inode flag in f2fs_inode.i_advise, which
> > isn't really appropriate since it's not a hint or advice. But
> > ->i_advise is already being used to hold the 'encrypt' flag; and F2FS's
> > ->i_flags uses the generic FS_* values, so it seems ->i_flags can't be
> > used for an F2FS-specific flag without additional work to remove the
> > assumption that ->i_flags uses the generic flags namespace.
>
> At a glance, this is a VFS feature, can we search free slot, and define
> FS_VERITY_FL like other generic flags, so we can intergrate this flag into
> f2fs_inode::i_flags?
Do we need to get/set this bit of i_flags to user? And, f2fs doesn't synchronize
it with inode block update. I think this should be set by internal f2fs
operations likewise fscrypt.
>
> And how about applying this patch inside the patchset of new fsverity feature?
> Since once fsverity feature has some design modification, I worry about that may
> be we need to change this bit? result in disk layout incompatibility.
The whole body is not fully mergeable, so once reserving the bits first, we can
support it f2fs-tools and prepare the feature in advance. Based on previous
fscrypt experience, I don't expect we need to modify or drop these dramatically
later.
Any thoughts?
>
> Thanks,
>
> >
> > [1] https://marc.info/?l=linux-fsdevel&m=151690752225644
> > [2] https://git.kernel.org/pub/scm/linux/kernel/git/mhalcrow/linux.git/log/?h=fs-verity-dev
> >
> > Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx>
> > ---
> > fs/f2fs/f2fs.h | 2 ++
> > 1 file changed, 2 insertions(+)
> >
> > diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> > index ae69dc358401..96d7809c4541 100644
> > --- a/fs/f2fs/f2fs.h
> > +++ b/fs/f2fs/f2fs.h
> > @@ -146,6 +146,7 @@ struct f2fs_mount_info {
> > #define F2FS_FEATURE_QUOTA_INO 0x0080
> > #define F2FS_FEATURE_INODE_CRTIME 0x0100
> > #define F2FS_FEATURE_LOST_FOUND 0x0200
> > +#define F2FS_FEATURE_VERITY 0x0400 /* reserved */
> >
> > #define F2FS_HAS_FEATURE(sb, mask) \
> > ((F2FS_SB(sb)->raw_super->feature & cpu_to_le32(mask)) != 0)
> > @@ -598,6 +599,7 @@ enum {
> > #define FADVISE_ENC_NAME_BIT 0x08
> > #define FADVISE_KEEP_SIZE_BIT 0x10
> > #define FADVISE_HOT_BIT 0x20
> > +#define FADVISE_VERITY_BIT 0x40 /* reserved */
> >
> > #define file_is_cold(inode) is_file(inode, FADVISE_COLD_BIT)
> > #define file_wrong_pino(inode) is_file(inode, FADVISE_LOST_PINO_BIT)
> >
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