On Wed, 2023-06-21 at 13:29 -0400, Tom Talpey wrote:
> On 6/21/2023 10:45 AM, Jeff Layton wrote:
> > struct timespec64 has unused bits in the tv_nsec field that can be used
> > for other purposes. In future patches, we're going to change how the
> > inode->i_ctime is accessed in certain inodes in order to make use of
> > them. In order to do that safely though, we'll need to eradicate raw
> > accesses of the inode->i_ctime field from the kernel.
> >
> > Add new accessor functions for the ctime that we can use to replace them.
> >
> > Signed-off-by: Jeff Layton <jlay...@kernel.org>
> > ---
> > fs/inode.c | 16 ++++++++++++++
> > include/linux/fs.h | 53 +++++++++++++++++++++++++++++++++++++++++++++-
> > 2 files changed, 68 insertions(+), 1 deletion(-)
> >
> > diff --git a/fs/inode.c b/fs/inode.c
> > index d37fad91c8da..c005e7328fbb 100644
> > --- a/fs/inode.c
> > +++ b/fs/inode.c
> > @@ -2499,6 +2499,22 @@ struct timespec64 current_time(struct inode *inode)
> > }
> > EXPORT_SYMBOL(current_time);
> >
> > +/**
> > + * inode_ctime_set_current - set the ctime to current_time
> > + * @inode: inode
> > + *
> > + * Set the inode->i_ctime to the current value for the inode. Returns
> > + * the current value that was assigned to i_ctime.
> > + */
> > +struct timespec64 inode_ctime_set_current(struct inode *inode)
> > +{
> > + struct timespec64 now = current_time(inode);
> > +
> > + inode_set_ctime(inode, now);
> > + return now;
> > +}
> > +EXPORT_SYMBOL(inode_ctime_set_current);
> > +
> > /**
> > * in_group_or_capable - check whether caller is CAP_FSETID privileged
> > * @idmap: idmap of the mount @inode was found from
> > diff --git a/include/linux/fs.h b/include/linux/fs.h
> > index 6867512907d6..9afb30606373 100644
> > --- a/include/linux/fs.h
> > +++ b/include/linux/fs.h
> > @@ -1474,7 +1474,58 @@ static inline bool fsuidgid_has_mapping(struct
> > super_block *sb,
> > kgid_has_mapping(fs_userns, kgid);
> > }
> >
> > -extern struct timespec64 current_time(struct inode *inode);
> > +struct timespec64 current_time(struct inode *inode);
> > +struct timespec64 inode_ctime_set_current(struct inode *inode);
> > +
> > +/**
> > + * inode_ctime_peek - fetch the current ctime from the inode
> > + * @inode: inode from which to fetch ctime
> > + *
> > + * Grab the current ctime from the inode and return it.
> > + */
> > +static inline struct timespec64 inode_ctime_peek(const struct inode *inode)
> > +{
> > + return inode->i_ctime;
> > +}
> > +
> > +/**
> > + * inode_ctime_set - set the ctime in the inode to the given value
> > + * @inode: inode in which to set the ctime
> > + * @ts: timespec value to set the ctime
> > + *
> > + * Set the ctime in @inode to @ts.
> > + */
> > +static inline struct timespec64 inode_ctime_set(struct inode *inode,
> > struct timespec64 ts)
> > +{
> > + inode->i_ctime = ts;
> > + return ts;
> > +}
> > +
> > +/**
> > + * inode_ctime_set_sec - set only the tv_sec field in the inode ctime
>
> I'm curious about why you choose to split the tv_sec and tv_nsec
> set_ functions. Do any callers not set them both? Wouldn't a
> single call enable a more atomic behavior someday?
>
> inode_ctime_set_sec_nsec(struct inode *, time64_t, time64_t)
>
> (or simply initialize a timespec64 and use inode_ctime_spec() )
>
Yes, quite a few places set the fields individually. For example, when
loading a value from disk that doesn't have sufficient granularity to
set the nsecs field to anything but 0.
Could I have done it by declaring a local timespec64 variable and just
use the inode_ctime_set function in these places? Absolutely.
That's a bit more difficult to handle with coccinelle though. If someone
wants to suggest a way to do that without having to change all of these
call sites manually, then I'm open to redoing the set.
That might be better left for a later cleanup though.
> > + * @inode: inode in which to set the ctime
> > + * @sec: value to set the tv_sec field
> > + *
> > + * Set the sec field in the ctime. Returns @sec.
> > + */
> > +static inline time64_t inode_ctime_set_sec(struct inode *inode, time64_t
> > sec)
> > +{
> > + inode->i_ctime.tv_sec = sec;
> > + return sec;
> > +}
> > +
> > +/**
> > + * inode_ctime_set_nsec - set only the tv_nsec field in the inode ctime
> > + * @inode: inode in which to set the ctime
> > + * @nsec: value to set the tv_nsec field
> > + *
> > + * Set the nsec field in the ctime. Returns @nsec.
> > + */
> > +static inline long inode_ctime_set_nsec(struct inode *inode, long nsec)
> > +{
> > + inode->i_ctime.tv_nsec = nsec;
> > + return nsec;
> > +}
> >
> > /*
> > * Snapshotting support.
--
Jeff Layton <jlay...@kernel.org>
