Re: [RFC 02/15] vfs: Change all structures to support 64 bit time

Arnd Bergmann
2016-01-19T22:25:19Z

On Wednesday 20 January 2016 07:49:46 Dave Chinner wrote:
> On Mon, Jan 18, 2016 at 09:27:13PM -0800, Deepa Dinamani wrote:
> > On Mon, Jan 18, 2016 at 5:38 PM, Dave Chinner <david@fromorbit.com> wrote:
> > > On Mon, Jan 18, 2016 at 10:46:07PM +0100, Arnd Bergmann wrote:
> > >> On Tuesday 19 January 2016 08:14:59 Dave Chinner wrote:
> > >> > On Mon, Jan 18, 2016 at 08:53:22PM +0100, Arnd Bergmann wrote:
> >
> > Let's back out a bit and consider a few changes with the suggested "abstraction":
> >
> > original code:
> >
> > extern void fat_time_fat2unix(struct msdos_sb_info *sbi, struct timespec *ts,
> > __le16 __time, __le16 __date, u8 time_cs);
> >
> > fat_time_fat2unix(sbi, &inode->i_mtime, de->time, de->date, 0);
> >
> > becomes ugly
> >
> > extern void fat_time_fat2unix(struct msdos_sb_info *sbi, struct timespec64 *ts,
> > __le16 __time, __le16 __date, u8 time_cs);
> >
> > struct timespec64 mtime = vfs_time_to_timespec64(i_mtime, inode);
> > fat_time_fat2unix(sbi, &mtime, de->time, de->date, 0);
>
> You're doing it wrong. fat_time_fat2unix() still gets passed
> &inode->i_mtime, and the function prototype is changed to a
> timespec64. *Nothing else needs to change*, because
> fat_time_fat2unix() does it own calculations and then stores the
> time directly into the timespec structure members....

That puts us back at the 'one big patch' problem: We can't change
fat_time_fat2unix() to pass a timespec64 until we also change
struct inode. The change may be small, but I see roughly 30 file
systems that assign i_?time into or from a local variable or pass it
into by reference into a function that is not from VFS.

see http://pastebin.com/BSnwJa1N for a list (certainly some false
positives and some false negatives in there)

Roughly two thirds of the instances can be handled easily using
vfs_time_to_timespec(), the others could be done much nicer
with additional helpers such as inode_timespec_compare()

> I think you're making a mountain out of a molehill. Most filesystems
> will be unchanged except for s/timespec/timespec64/ as they store
> values directly into timespec members when encoding/decoding. There
> is no need for timestamp conversion in places like this - you're
> simply not looking deep enough and applying the conversion at the
> wrong layer.

Any idea how to improve this somewhat lacking patch?

diff --git a/fs/xfs/xfs_trans_inode.c b/fs/xfs/xfs_trans_inode.c
index b97f1df910ab..7fbb07dcad36 100644
--- a/fs/xfs/xfs_trans_inode.c
+++ b/fs/xfs/xfs_trans_inode.c
@@ -68,22 +68,24 @@ xfs_trans_ichgtime(
int flags)
{
struct inode *inode = VFS_I(ip);
- struct timespec tv;
+ struct timespec tv, mtime, ctime;

ASSERT(tp);
ASSERT(xfs_isilocked(ip, XFS_ILOCK_EXCL));

- tv = current_fs_time(inode->i_sb);
+ tv = vfs_time_to_timespec(current_fs_time(inode->i_sb));
+ mtime = vfs_time_to_timespec(inode->i_mtime);
+ ctime = vfs_time_to_timespec(inode->i_ctime);

if ((flags & XFS_ICHGTIME_MOD) &&
- !timespec_equal(&inode->i_mtime, &tv)) {
- inode->i_mtime = tv;
+ !timespec_equal(&mtime, &tv)) {
+ inode->i_mtime = timespec_to_vfs_time(tv);
ip->i_d.di_mtime.t_sec = tv.tv_sec;
ip->i_d.di_mtime.t_nsec = tv.tv_nsec;
}
if ((flags & XFS_ICHGTIME_CHG) &&
- !timespec_equal(&inode->i_ctime, &tv)) {
- inode->i_ctime = tv;
+ !timespec_equal(&ctime, &tv)) {
+ inode->i_ctime = timespec_to_vfs_time(tv);
ip->i_d.di_ctime.t_sec = tv.tv_sec;
ip->i_d.di_ctime.t_nsec = tv.tv_nsec;
}

The way that Deepa suggests I think would turn out as:

diff --git a/fs/xfs/xfs_trans_inode.c b/fs/xfs/xfs_trans_inode.c
index b97f1df910ab..54fc3c41047a 100644
--- a/fs/xfs/xfs_trans_inode.c
+++ b/fs/xfs/xfs_trans_inode.c
@@ -68,7 +68,7 @@ xfs_trans_ichgtime(
int flags)
{
struct inode *inode = VFS_I(ip);
- struct timespec tv;
+ struct vfs_time tv;

ASSERT(tp);
ASSERT(xfs_isilocked(ip, XFS_ILOCK_EXCL));
@@ -76,13 +76,13 @@ xfs_trans_ichgtime(
tv = current_fs_time(inode->i_sb);

if ((flags & XFS_ICHGTIME_MOD) &&
- !timespec_equal(&inode->i_mtime, &tv)) {
+ !vfs_time_equal(&inode->i_mtime, &tv)) {
inode->i_mtime = tv;
ip->i_d.di_mtime.t_sec = tv.tv_sec;
ip->i_d.di_mtime.t_nsec = tv.tv_nsec;
}
if ((flags & XFS_ICHGTIME_CHG) &&
- !timespec_equal(&inode->i_ctime, &tv)) {
+ !vfs_time_equal(&inode->i_ctime, &tv)) {
inode->i_ctime = tv;
ip->i_d.di_ctime.t_sec = tv.tv_sec;
ip->i_d.di_ctime.t_nsec = tv.tv_nsec;

which I would much prefer here.

Arnd