[RFC 00/32] making inode time stamps y2038 ready

[RFC 00/32] making inode time stamps y2038 ready

[Arnd Bergmann]

Based on the recent discussion about 64-bit time_t for new
architectures, and for solving the year 2038 problem in general,
I decided to try out what it would take to solve part of the
kernel side of things.

This is a proof-of-concept work to get us to the point where
two system calls (utimes and stat) provide a working interface
to user space to pass 64-bit inode time stamps in and out of
the kernel all the way to the file systems.

I picked this because it is a fairly isolated problem, as the
inode time stamps are rarely assigned to any other time values.
As a byproduct of this work, I documented for each of the file
systems we support how long the on-disk format can work[1].

Obviously we also need to convert all the other syscalls and
have a proper libc implementation using those for this to
be really useful, but it's a start and it can be tested
independently (I didn't so far, want to wait for initial
feedback).

All the interesting stuff is in the first five patches here,
the rest is the straightforward conversion of all file systems
that use 'timespec' values internally.

There are of course a number of open questions:

a) is this the right approach in general? The previous discussion
   pointed this way, but there may be other opinions.
b) what type should we use internally to represent inode time
   stamps? The code contains three different versions that would
   all work, we just have to pick a good tradeoff between
   efficiency and the range of times we want to cover.
c) Should we continue this way for all 32-bit platforms for
   consistency, including future ones, or should we go to
   different 64-bit types right away? My feeling is that the
   second approach would complicate this work.

	Arnd

[1] http://kernelnewbies.org/y2038

Arnd Bergmann (32):
  fs: introduce new 'struct inode_time'
  uapi: add struct __kernel_timespec{32,64}
  fs: introduce sys_utimens64at
  fs: introduce sys_newfstat64/sys_newfstatat64
  arch: hook up new stat and utimes syscalls
  isofs: fix timestamps beyond 2027
  fs/nfs: convert to struct inode_time
  fs/ceph: convert to 'struct inode_time'
  fs/pstore: convert to struct inode_time
  fs/coda: convert to struct inode_time
  xfs: convert to struct inode_time
  btrfs: convert to struct inode_time
  ext3: convert to struct inode_time
  ext4: convert to struct inode_time
  cifs: convert to struct inode_time
  ntfs: convert to struct inode_time
  ubifs: convert to struct inode_time
  ocfs2: convert to struct inode_time
  fs/fat: convert to struct inode_time
  afs: convert to struct inode_time
  udf: convert to struct inode_time
  fs: convert simple fs to inode_time
  logfs: convert to struct inode_time
  hfs, hfsplus: convert to struct inode_time
  gfs2: convert to struct inode_time
  reiserfs: convert to struct inode_time
  jffs2: convert to struct inode_time
  adfs: convert to struct inode_time
  f2fs: convert to struct inode_time
  fuse: convert to struct inode_time
  scsi: fnic: use current_kernel_time() for timestamp
  fs: use new inode_time definition unconditionally

 arch/alpha/kernel/osf_sys.c        |  2 +-
 arch/arm/include/asm/unistd.h      |  2 +-
 arch/arm/include/uapi/asm/stat.h   | 25 +++++++++++++++++
 arch/arm/include/uapi/asm/unistd.h |  3 +++
 arch/arm/kernel/calls.S            |  3 +++
 arch/arm64/include/asm/unistd32.h  |  5 +++-
 arch/x86/include/uapi/asm/stat.h   | 28 +++++++++++++++++++
 arch/x86/syscalls/syscall_32.tbl   |  3 +++
 drivers/block/rbd.c                |  2 +-
 drivers/firmware/efi/efi-pstore.c  | 28 +++++++++----------
 drivers/scsi/fnic/fnic_trace.c     |  2 +-
 drivers/tty/tty_io.c               |  2 +-
 drivers/usb/gadget/f_fs.c          |  2 +-
 fs/adfs/inode.c                    |  4 +--
 fs/afs/afs.h                       |  6 ++---
 fs/afs/fsclient.c                  |  2 +-
 fs/attr.c                          |  8 +++---
 fs/btrfs/file.c                    |  6 ++---
 fs/btrfs/inode.c                   |  4 +--
 fs/btrfs/ioctl.c                   |  4 +--
 fs/btrfs/root-tree.c               |  2 +-
 fs/btrfs/transaction.c             |  2 +-
 fs/ceph/cache.c                    |  2 +-
 fs/ceph/caps.c                     |  6 ++---
 fs/ceph/file.c                     |  4 +--
 fs/ceph/inode.c                    | 20 +++++++-------
 fs/ceph/super.h                    |  8 +++---
 fs/cifs/cache.c                    |  6 ++---
 fs/cifs/cifsglob.h                 |  6 ++---
 fs/cifs/cifsproto.h                |  6 ++---
 fs/cifs/cifssmb.c                  |  5 ++--
 fs/cifs/inode.c                    |  2 +-
 fs/cifs/netmisc.c                  | 15 ++++++-----
 fs/coda/coda_linux.c               | 18 ++++++++-----
 fs/compat.c                        | 19 ++-----------
 fs/configfs/inode.c                |  6 ++---
 fs/cramfs/inode.c                  |  2 +-
 fs/ext3/inode.c                    |  4 +--
 fs/ext4/ext4.h                     | 10 +++----
 fs/ext4/extents.c                  |  2 +-
 fs/f2fs/file.c                     |  6 ++---
 fs/fat/dir.c                       |  2 +-
 fs/fat/fat.h                       |  6 ++---
 fs/fat/misc.c                      |  4 +--
 fs/fat/namei_msdos.c               |  8 +++---
 fs/fat/namei_vfat.c                | 10 +++----
 fs/fuse/inode.c                    |  6 ++---
 fs/gfs2/dir.c                      |  6 ++---
 fs/gfs2/glops.c                    |  4 +--
 fs/hfs/hfs_fs.h                    |  2 +-
 fs/hfsplus/hfsplus_fs.h            |  2 +-
 fs/inode.c                         | 18 ++++++-------
 fs/isofs/util.c                    |  2 +-
 fs/jffs2/os-linux.h                |  2 +-
 fs/locks.c                         |  4 +--
 fs/logfs/readwrite.c               | 18 ++++++-------
 fs/nfs/callback.h                  |  4 +--
 fs/nfs/callback_xdr.c              |  6 ++---
 fs/nfs/file.c                      |  2 +-
 fs/nfs/fscache-index.c             |  8 +++---
 fs/nfs/inode.c                     | 10 +++----
 fs/nfs/internal.h                  |  4 +--
 fs/nfs/netns.h                     |  2 +-
 fs/nfs/nfs2xdr.c                   |  8 +++---
 fs/nfs/nfs3xdr.c                   | 10 +++----
 fs/nfs/nfs4xdr.c                   | 20 +++++++-------
 fs/nfsd/nfs3xdr.c                  |  6 ++---
 fs/nfsd/nfsfh.h                    |  4 +--
 fs/nfsd/nfsxdr.c                   |  2 +-
 fs/ntfs/inode.c                    | 12 ++++-----
 fs/ntfs/time.h                     |  8 +++---
 fs/ocfs2/dlmglue.c                 | 16 +++++------
 fs/ocfs2/file.c                    |  6 ++---
 fs/ocfs2/ocfs2.h                   |  2 +-
 fs/pstore/inode.c                  |  2 +-
 fs/pstore/internal.h               |  2 +-
 fs/pstore/platform.c               |  2 +-
 fs/pstore/ram.c                    | 18 +++++++------
 fs/reiserfs/namei.c                |  2 +-
 fs/reiserfs/xattr.c                |  4 +--
 fs/stat.c                          | 55 ++++++++++++++++++++++++++++++++++++++
 fs/ubifs/dir.c                     |  2 +-
 fs/ubifs/file.c                    | 16 +++++------
 fs/ubifs/misc.h                    |  2 +-
 fs/udf/udf_i.h                     |  2 +-
 fs/udf/udf_sb.h                    |  2 +-
 fs/udf/udfdecl.h                   |  7 ++---
 fs/udf/udftime.c                   |  7 ++---
 fs/utimes.c                        | 47 +++++++++++++++++++++++++++-----
 fs/xfs/time.h                      |  4 +--
 fs/xfs/xfs_inode.c                 |  2 +-
 fs/xfs/xfs_iops.c                  |  2 +-
 fs/xfs/xfs_trans_inode.c           |  6 ++---
 include/linux/ceph/decode.h        |  8 +++---
 include/linux/ceph/osd_client.h    |  4 +--
 include/linux/compat.h             |  2 +-
 include/linux/fs.h                 | 32 +++++++++++-----------
 include/linux/nfs_fs_sb.h          |  2 +-
 include/linux/nfs_xdr.h            | 14 +++++-----
 include/linux/pstore.h             |  4 +--
 include/linux/stat.h               |  6 ++---
 include/linux/syscalls.h           |  9 ++++++-
 include/linux/time.h               | 44 +++++++++++++++++++++++++++---
 include/uapi/asm-generic/stat.h    | 29 ++++++++++++++++++--
 include/uapi/asm-generic/unistd.h  |  8 +++++-
 include/uapi/linux/coda.h          |  1 +
 include/uapi/linux/time.h          | 40 ++++++++++++++++++++++++++-
 init/initramfs.c                   |  2 +-
 kernel/audit.c                     |  2 +-
 kernel/auditsc.c                   |  2 +-
 kernel/time.c                      | 44 +++++++++++++++++++++++++-----
 kernel/time/timekeeping.c          | 16 +++++++++++
 net/ceph/auth_x.c                  |  2 +-
 net/ceph/osd_client.c              |  4 +--
 114 files changed, 642 insertions(+), 333 deletions(-)

-- 
1.8.3.2

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[RFC 12/32] btrfs: convert to struct inode_time

[Arnd Bergmann]

btrfs uses unsigned 64-bit seconds for inode timestamps, which will work
basically forever, but the VFS uses struct timespec for timestamps,
which is only good until 2038 on 32-bit CPUs.

This gets us one small step closer to lifting the VFS limit by using
struct inode_time in btrfs.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Chris Mason <clm@fb.com>
Cc: Josef Bacik <jbacik@fb.com>
Cc: linux-btrfs@vger.kernel.org
---
 fs/btrfs/file.c        | 6 +++---
 fs/btrfs/inode.c       | 4 ++--
 fs/btrfs/ioctl.c       | 4 ++--
 fs/btrfs/root-tree.c   | 2 +-
 fs/btrfs/transaction.c | 2 +-
 5 files changed, 9 insertions(+), 9 deletions(-)

diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index a58df83..3e16a4e 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -1693,16 +1693,16 @@ out:
 
 static void update_time_for_write(struct inode *inode)
 {
-	struct timespec now;
+	struct inode_time now;
 
 	if (IS_NOCMTIME(inode))
 		return;
 
 	now = current_fs_time(inode->i_sb);
-	if (!timespec_equal(&inode->i_mtime, &now))
+	if (!inode_time_equal(&inode->i_mtime, &now))
 		inode->i_mtime = now;
 
-	if (!timespec_equal(&inode->i_ctime, &now))
+	if (!inode_time_equal(&inode->i_ctime, &now))
 		inode->i_ctime = now;
 
 	if (IS_I_VERSION(inode))
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 2ac3036..d825387 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -5440,7 +5440,7 @@ static int btrfs_dirty_inode(struct inode *inode)
  * This is a copy of file_update_time.  We need this so we can return error on
  * ENOSPC for updating the inode in the case of file write and mmap writes.
  */
-static int btrfs_update_time(struct inode *inode, struct timespec *now,
+static int btrfs_update_time(struct inode *inode, struct inode_time *now,
 			     int flags)
 {
 	struct btrfs_root *root = BTRFS_I(inode)->root;
@@ -8223,7 +8223,7 @@ static int btrfs_rename(struct inode *old_dir, struct dentry *old_dentry,
 	struct btrfs_root *dest = BTRFS_I(new_dir)->root;
 	struct inode *new_inode = new_dentry->d_inode;
 	struct inode *old_inode = old_dentry->d_inode;
-	struct timespec ctime = CURRENT_TIME;
+	struct inode_time ctime = CURRENT_TIME;
 	u64 index = 0;
 	u64 root_objectid;
 	int ret;
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index a313ab0..2de5f86 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -435,7 +435,7 @@ static noinline int create_subvol(struct inode *dir,
 	struct btrfs_root *root = BTRFS_I(dir)->root;
 	struct btrfs_root *new_root;
 	struct btrfs_block_rsv block_rsv;
-	struct timespec cur_time = CURRENT_TIME;
+	struct inode_time cur_time = CURRENT_TIME;
 	struct inode *inode;
 	int ret;
 	int err;
@@ -4456,7 +4456,7 @@ static long _btrfs_ioctl_set_received_subvol(struct file *file,
 	struct btrfs_root *root = BTRFS_I(inode)->root;
 	struct btrfs_root_item *root_item = &root->root_item;
 	struct btrfs_trans_handle *trans;
-	struct timespec ct = CURRENT_TIME;
+	struct inode_time ct = CURRENT_TIME;
 	int ret = 0;
 	int received_uuid_changed;
 
diff --git a/fs/btrfs/root-tree.c b/fs/btrfs/root-tree.c
index 38bb47e..344e89f 100644
--- a/fs/btrfs/root-tree.c
+++ b/fs/btrfs/root-tree.c
@@ -487,7 +487,7 @@ void btrfs_update_root_times(struct btrfs_trans_handle *trans,
 			     struct btrfs_root *root)
 {
 	struct btrfs_root_item *item = &root->root_item;
-	struct timespec ct = CURRENT_TIME;
+	struct inode_time ct = CURRENT_TIME;
 
 	spin_lock(&root->root_item_lock);
 	btrfs_set_root_ctransid(item, trans->transid);
diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index 7579f6d..09dcc8a 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -1133,7 +1133,7 @@ static noinline int create_pending_snapshot(struct btrfs_trans_handle *trans,
 	struct dentry *dentry;
 	struct extent_buffer *tmp;
 	struct extent_buffer *old;
-	struct timespec cur_time = CURRENT_TIME;
+	struct inode_time cur_time = CURRENT_TIME;
 	int ret = 0;
 	u64 to_reserve = 0;
 	u64 index = 0;
-- 
1.8.3.2

Re: [RFC 00/32] making inode time stamps y2038 ready

[Vyacheslav Dubeyko]

Hi Arnd,

On Fri, 2014-05-30 at 22:01 +0200, Arnd Bergmann wrote:

[snip]
> 
> Arnd Bergmann (32):
>   fs: introduce new 'struct inode_time'
>   uapi: add struct __kernel_timespec{32,64}
>   fs: introduce sys_utimens64at
>   fs: introduce sys_newfstat64/sys_newfstatat64
>   arch: hook up new stat and utimes syscalls
>   isofs: fix timestamps beyond 2027
>   fs/nfs: convert to struct inode_time
>   fs/ceph: convert to 'struct inode_time'
>   fs/pstore: convert to struct inode_time
>   fs/coda: convert to struct inode_time
>   xfs: convert to struct inode_time
>   btrfs: convert to struct inode_time
>   ext3: convert to struct inode_time
>   ext4: convert to struct inode_time
>   cifs: convert to struct inode_time
>   ntfs: convert to struct inode_time
>   ubifs: convert to struct inode_time
>   ocfs2: convert to struct inode_time
>   fs/fat: convert to struct inode_time
>   afs: convert to struct inode_time
>   udf: convert to struct inode_time
>   fs: convert simple fs to inode_time
>   logfs: convert to struct inode_time
>   hfs, hfsplus: convert to struct inode_time
>   gfs2: convert to struct inode_time
>   reiserfs: convert to struct inode_time
>   jffs2: convert to struct inode_time
>   adfs: convert to struct inode_time
>   f2fs: convert to struct inode_time
>   fuse: convert to struct inode_time
>   scsi: fnic: use current_kernel_time() for timestamp
>   fs: use new inode_time definition unconditionally
> 

By the way, what about NILFS2? Is NILFS2 ready for suggested approach
without any changes?

Thanks,
Vyacheslav Dubeyko.

Re: [RFC 00/32] making inode time stamps y2038 ready

[Richard Cochran]

On Fri, May 30, 2014 at 10:01:24PM +0200, Arnd Bergmann wrote:
> 
> I picked this because it is a fairly isolated problem, as the
> inode time stamps are rarely assigned to any other time values.
> As a byproduct of this work, I documented for each of the file
> systems we support how long the on-disk format can work[1].

Why are some of the time stamp expiration dates marked as "never"?

Thanks,
Richard

Re: [RFC 00/32] making inode time stamps y2038 ready

[Arnd Bergmann]

On Saturday 31 May 2014 16:51:15 Richard Cochran wrote:
> On Fri, May 30, 2014 at 10:01:24PM +0200, Arnd Bergmann wrote:
> > 
> > I picked this because it is a fairly isolated problem, as the
> > inode time stamps are rarely assigned to any other time values.
> > As a byproduct of this work, I documented for each of the file
> > systems we support how long the on-disk format can work[1].
> 
> Why are some of the time stamp expiration dates marked as "never"?

It's an approximation:
with 64-bit timestamps, you can represent close to 300 billion
years, which is way past the time that our planet can sustain
life of any form[1].

	Arnd

[1] http://en.wikipedia.org/wiki/Timeline_of_the_far_future

Re: [RFC 00/32] making inode time stamps y2038 ready

[Richard Cochran]

On Sat, May 31, 2014 at 05:23:02PM +0200, Arnd Bergmann wrote:
> 
> It's an approximation:

(Approximately never ;)

> with 64-bit timestamps, you can represent close to 300 billion
> years, which is way past the time that our planet can sustain
> life of any form[1].

Did you mean mean 64 bits worth of seconds?

  2^64 / (3600*24*365) = 584,942,417,355

That is more than 300 billion years, and still, it is not quite the
same as "never".

In any case, that term is not too helpful in the comparison table,
IMHO. One could think that some sort of clever running count relative
to the last mount time was implied.

Thanks,
Richard

[1] You are forgetting the immortal robotic overlords.

Re: [RFC 00/32] making inode time stamps y2038 ready

[H. Peter Anvin]

Typically they are using 64-bit signed seconds.

On May 31, 2014 11:22:37 AM PDT, Richard Cochran <richardcochran@gmail.com> wrote:
>On Sat, May 31, 2014 at 05:23:02PM +0200, Arnd Bergmann wrote:
>> 
>> It's an approximation:
>
>(Approximately never ;)
>
>> with 64-bit timestamps, you can represent close to 300 billion
>> years, which is way past the time that our planet can sustain
>> life of any form[1].
>
>Did you mean mean 64 bits worth of seconds?
>
>  2^64 / (3600*24*365) = 584,942,417,355
>
>That is more than 300 billion years, and still, it is not quite the
>same as "never".
>
>In any case, that term is not too helpful in the comparison table,
>IMHO. One could think that some sort of clever running count relative
>to the last mount time was implied.
>
>Thanks,
>Richard
>
>[1] You are forgetting the immortal robotic overlords.

-- 
Sent from my mobile phone.  Please pardon brevity and lack of formatting.

Re: [RFC 00/32] making inode time stamps y2038 ready

[Richard Cochran]

On Sat, May 31, 2014 at 05:23:02PM +0200, Arnd Bergmann wrote:
> On Saturday 31 May 2014 16:51:15 Richard Cochran wrote:
> > 
> > Why are some of the time stamp expiration dates marked as "never"?
> 
> It's an approximation:

Also, the term "never" might mean using arbitrarily long integers
as in ASN.1.

Thanks,
Richard

Re: [RFC 00/32] making inode time stamps y2038 ready

[Richard Cochran]

On Sat, May 31, 2014 at 12:34:12PM -0700, H. Peter Anvin wrote:
> Typically they are using 64-bit signed seconds.

Okay, that is what I wanted to know.

Thanks,
Richard

Re: [RFC 00/32] making inode time stamps y2038 ready

[Joseph S. Myers]

On Fri, 30 May 2014, Arnd Bergmann wrote:

> a) is this the right approach in general? The previous discussion
>    pointed this way, but there may be other opinions.

The syscall changes seem like the sort of thing I'd expect, although 
patches adding new syscalls or otherwise affecting the kernel/userspace 
interface (as opposed to those relating to an individual filesystem) 
should go to linux-api as well as other relevant lists.

-- 
Joseph S. Myers
joseph@codesourcery.com

Re: [RFC 00/32] making inode time stamps y2038 ready

[Arnd Bergmann]

On Monday 02 June 2014 13:52:19 Joseph S. Myers wrote:
> On Fri, 30 May 2014, Arnd Bergmann wrote:
> 
> > a) is this the right approach in general? The previous discussion
> >    pointed this way, but there may be other opinions.
> 
> The syscall changes seem like the sort of thing I'd expect, although 
> patches adding new syscalls or otherwise affecting the kernel/userspace 
> interface (as opposed to those relating to an individual filesystem) 
> should go to linux-api as well as other relevant lists.

Ok. Sorry about missing linux-api, I confused it with linux-arch, which
may not be as relevant here, except for the one question whether we
actually want to have the new ABI on all 32-bit architectures or only
as an opt-in for those that expect to stay around for another 24 years.

Two more questions for you:

- are you (and others) happy with adding this type of stat syscall
  (fstatat64/fstat64) as opposed to the more generic xstat that has
  been discussed in the past and that never made it through the bike-
  shedding discussion?

- once we have enough buy-in from reviewers to merge this initial
  series, should we proceed to define rest of the syscall ABI
  (minus driver ioctls) so glibc and kernel can do the conversion
  on top of that, or should we better try to do things one syscall
  family at a time and actually get the kernel to handle them
  correctly internally?

	Arnd

Re: [RFC 00/32] making inode time stamps y2038 ready

[H. Peter Anvin]

On 06/02/2014 12:19 PM, Arnd Bergmann wrote:
> On Monday 02 June 2014 13:52:19 Joseph S. Myers wrote:
>> On Fri, 30 May 2014, Arnd Bergmann wrote:
>>
>>> a) is this the right approach in general? The previous discussion
>>>    pointed this way, but there may be other opinions.
>>
>> The syscall changes seem like the sort of thing I'd expect, although 
>> patches adding new syscalls or otherwise affecting the kernel/userspace 
>> interface (as opposed to those relating to an individual filesystem) 
>> should go to linux-api as well as other relevant lists.
> 
> Ok. Sorry about missing linux-api, I confused it with linux-arch, which
> may not be as relevant here, except for the one question whether we
> actually want to have the new ABI on all 32-bit architectures or only
> as an opt-in for those that expect to stay around for another 24 years.
> 
> Two more questions for you:
> 
> - are you (and others) happy with adding this type of stat syscall
>   (fstatat64/fstat64) as opposed to the more generic xstat that has
>   been discussed in the past and that never made it through the bike-
>   shedding discussion?
> 
> - once we have enough buy-in from reviewers to merge this initial
>   series, should we proceed to define rest of the syscall ABI
>   (minus driver ioctls) so glibc and kernel can do the conversion
>   on top of that, or should we better try to do things one syscall
>   family at a time and actually get the kernel to handle them
>   correctly internally?
> 

The bit that is really going to hurt is every single ioctl that uses a
timespec.

Honestly, though, I really don't understand the point with "struct
inode_time".  It seems like the zeroeth-order thing is to change the
kernel internal version of struct timespec to have a 64-bit time... it
isn't just about inodes.  We then should be explicit about the external
uses of time, and use accessors.

	-hpa

Re: [RFC 00/32] making inode time stamps y2038 ready

[Arnd Bergmann]

On Monday 02 June 2014 12:26:22 H. Peter Anvin wrote:
> On 06/02/2014 12:19 PM, Arnd Bergmann wrote:
> > On Monday 02 June 2014 13:52:19 Joseph S. Myers wrote:
> >> On Fri, 30 May 2014, Arnd Bergmann wrote:
> >>
> >>> a) is this the right approach in general? The previous discussion
> >>>    pointed this way, but there may be other opinions.
> >>
> >> The syscall changes seem like the sort of thing I'd expect, although 
> >> patches adding new syscalls or otherwise affecting the kernel/userspace 
> >> interface (as opposed to those relating to an individual filesystem) 
> >> should go to linux-api as well as other relevant lists.
> > 
> > Ok. Sorry about missing linux-api, I confused it with linux-arch, which
> > may not be as relevant here, except for the one question whether we
> > actually want to have the new ABI on all 32-bit architectures or only
> > as an opt-in for those that expect to stay around for another 24 years.
> > 
> > Two more questions for you:
> > 
> > - are you (and others) happy with adding this type of stat syscall
> >   (fstatat64/fstat64) as opposed to the more generic xstat that has
> >   been discussed in the past and that never made it through the bike-
> >   shedding discussion?
> > 
> > - once we have enough buy-in from reviewers to merge this initial
> >   series, should we proceed to define rest of the syscall ABI
> >   (minus driver ioctls) so glibc and kernel can do the conversion
> >   on top of that, or should we better try to do things one syscall
> >   family at a time and actually get the kernel to handle them
> >   correctly internally?
> > 
> 
> The bit that is really going to hurt is every single ioctl that uses a
> timespec.
> 
> Honestly, though, I really don't understand the point with "struct
> inode_time".  It seems like the zeroeth-order thing is to change the
> kernel internal version of struct timespec to have a 64-bit time... it
> isn't just about inodes.  We then should be explicit about the external
> uses of time, and use accessors.

I picked these because they are fairly isolated from all other uses,
in particular since inode times are the only things where we really
care about times in the distant past or future (decades away as opposed
to things that happened between boot and shutdown).

For other kernel-internal uses, we may be better off migrating to
a completely different representation, such as nanoseconds since
boot or the architecture specific ktime_t, but this is really something
to decide for each subsystem.

I just tried building an arm32 kernel with a s64 time_t, and that
failed horribly, I get linker errors for missing 64-bit divides
and lots of warnings for code that expects time_t pointers to
functions taking a 'long' or vice versa. I also think the only
way to maintain ABI compatibility is to separate the internal uses
from the interface, which means auditing all code in the end.

	Arnd

Re: [RFC 00/32] making inode time stamps y2038 ready

[Joseph S. Myers]

On Mon, 2 Jun 2014, Arnd Bergmann wrote:

> Ok. Sorry about missing linux-api, I confused it with linux-arch, which
> may not be as relevant here, except for the one question whether we
> actually want to have the new ABI on all 32-bit architectures or only
> as an opt-in for those that expect to stay around for another 24 years.

For glibc I think it will make the most sense to add the support for 
64-bit time_t across all architectures that currently have 32-bit time_t 
(with the new interfaces having fallback support to implementation in 
terms of the 32-bit kernel interfaces, if the 64-bit syscalls are 
unavailable either at runtime or in the kernel headers against which glibc 
is compiled - this fallback code will of course need to check for overflow 
when passing a time value to the kernel, hopefully with error handling 
consistent with whatever the kernel ends up doing when a filesystem can't 
support a timestamp).  If some architectures don't provide the new 
interfaces in the kernel then that will mean the fallback code in glibc 
can't be removed until glibc support for those architectures is removed 
(as opposed to removing it when glibc no longer supports kernels predating 
the kernel support).

> Two more questions for you:
> 
> - are you (and others) happy with adding this type of stat syscall
>   (fstatat64/fstat64) as opposed to the more generic xstat that has
>   been discussed in the past and that never made it through the bike-
>   shedding discussion?

I am.

> - once we have enough buy-in from reviewers to merge this initial
>   series, should we proceed to define rest of the syscall ABI
>   (minus driver ioctls) so glibc and kernel can do the conversion
>   on top of that, or should we better try to do things one syscall
>   family at a time and actually get the kernel to handle them
>   correctly internally?

I don't have any comments on that ordering question.

-- 
Joseph S. Myers
joseph@codesourcery.com

Re: [RFC 00/32] making inode time stamps y2038 ready

[H. Peter Anvin]

On 06/02/2014 12:55 PM, Arnd Bergmann wrote:
>>
>> The bit that is really going to hurt is every single ioctl that uses a
>> timespec.
>>
>> Honestly, though, I really don't understand the point with "struct
>> inode_time".  It seems like the zeroeth-order thing is to change the
>> kernel internal version of struct timespec to have a 64-bit time... it
>> isn't just about inodes.  We then should be explicit about the external
>> uses of time, and use accessors.
> 
> I picked these because they are fairly isolated from all other uses,
> in particular since inode times are the only things where we really
> care about times in the distant past or future (decades away as opposed
> to things that happened between boot and shutdown).
> 

If nothing else, I would expect to be able to set the system time to
weird values for testing.  So I'm not so sure I agree with that...

> For other kernel-internal uses, we may be better off migrating to
> a completely different representation, such as nanoseconds since
> boot or the architecture specific ktime_t, but this is really something
> to decide for each subsystem.

Having a bunch of different time representations in the kernel seems
like a real headache...

	-hpa

Re: [RFC 00/32] making inode time stamps y2038 ready

[Arnd Bergmann]

On Saturday 31 May 2014 18:30:49 Vyacheslav Dubeyko wrote:
> By the way, what about NILFS2? Is NILFS2 ready for suggested approach
> without any changes?

nilfs2 and a lot of other file systems don't need any changes for
this, because they don't assign the inode time stamp fields to
a 'struct timespec'.

FWIW, nilfs2 uses a 64-bit seconds value, which is always safe and
can represent the full range of user space timespec on all machines.

	Arnd

Re: [RFC 00/32] making inode time stamps y2038 ready

[Arnd Bergmann]

On Monday 02 June 2014 14:57:26 H. Peter Anvin wrote:
> On 06/02/2014 12:55 PM, Arnd Bergmann wrote:
> >>
> >> The bit that is really going to hurt is every single ioctl that uses a
> >> timespec.
> >>
> >> Honestly, though, I really don't understand the point with "struct
> >> inode_time".  It seems like the zeroeth-order thing is to change the
> >> kernel internal version of struct timespec to have a 64-bit time... it
> >> isn't just about inodes.  We then should be explicit about the external
> >> uses of time, and use accessors.
> > 
> > I picked these because they are fairly isolated from all other uses,
> > in particular since inode times are the only things where we really
> > care about times in the distant past or future (decades away as opposed
> > to things that happened between boot and shutdown).
> > 
> 
> If nothing else, I would expect to be able to set the system time to
> weird values for testing.  So I'm not so sure I agree with that...

I think John Stultz and Thomas Gleixner have already started looking
at how the timekeeping code can be updated. Once that is done, we should
be able to add a functional 64-bit gettimeofday/settimeofday syscall
pair. While I definitely agree this is one of the most basic things to
have, it's also not an area of the kernel that is easy to change.

> > For other kernel-internal uses, we may be better off migrating to
> > a completely different representation, such as nanoseconds since
> > boot or the architecture specific ktime_t, but this is really something
> > to decide for each subsystem.
> 
> Having a bunch of different time representations in the kernel seems
> like a real headache...

We already have time_t, ktime_t, timeval, timespec, compat_timespec,
clock_t, cputime_t, cputime64_t, tm, nanoseconds, jiffies, jiffies64,
and lots of driver or file system specific representations. I'm all for
removing a bunch of these from the kernel, but my feeling is that this is
one of the cases where we first have to add new ones in order to remove
those that are already there.
To complicate things further, we also have various times bases
(realtime/utc, realtime/tai, monotonic, monotonic_raw, boottime, ...),
and at least for the timespec values we pass around, it's not always
obvious which one is used, of if that's the right one.

We probably don't want to add a lot of new representations, and it's
possible that we can change most of the internal code we have to
ktime_t and then convert that to whatever user space wants at the
interfaces.

The possible uses I can see for non-ktime_t types in the kernel are:
* inodes need 96 bit timestamps to represent the full range of values
  that can be stored in a file system, you made a convincing argument
  for that. Almost everything else can fit into 64 bit on a 32-bit
  kernel, in theory also on a 64-bit kernel if we want that.
* A number of interfaces pass relative timespecs: nanosleep(), poll(),
  select(), sigtimedwait(), alarm(), futex() and probably more. There is
  nothing wrong with the use of timespec here, and it may be good to
  annotate that by using a new type (e.g. struct timeout) that is defined
  as compatible with the current timespec.
* For new user interfaces, we need a new type such as the
  __kernel_timespec64 I introduced, so it doesn't clash with the normal
  user timespec that may be smaller, depending on the libc.
* A lot of drivers will need new ioctl commands, and for drivers that
  just need time stamps (audio, v4l, sockets, ...) it may be more
  efficient and more correct to use a new timestamp_t (e.g. boot time
  64-bit nanoseconds) than __kernel_timespec64, which is not normally
  monotonic and requires a normalization step. If we end up introducing
  such a type in the user interface, we can also start using it in the
  kernel.

	Arnd

Re: [RFC 00/32] making inode time stamps y2038 ready

[Joseph S. Myers]

On Tue, 3 Jun 2014, Arnd Bergmann wrote:

> I think John Stultz and Thomas Gleixner have already started looking
> at how the timekeeping code can be updated. Once that is done, we should
> be able to add a functional 64-bit gettimeofday/settimeofday syscall
> pair. While I definitely agree this is one of the most basic things to
> have, it's also not an area of the kernel that is easy to change.

64-bit clock_gettime / clock_settime instead of gettimeofday / 
settimeofday should avoid the need for the kernel to have a 64-bit version 
of struct timeval.  (Userspace 64-bit gettimeofday / settimeofday would 
need to use a combination of the syscalls if the tz pointer is non-NULL.)

-- 
Joseph S. Myers
joseph@codesourcery.com

Re: [RFC 00/32] making inode time stamps y2038 ready

[Arnd Bergmann]

On Tuesday 03 June 2014 14:33:10 Joseph S. Myers wrote:
> On Tue, 3 Jun 2014, Arnd Bergmann wrote:
> 
> > I think John Stultz and Thomas Gleixner have already started looking
> > at how the timekeeping code can be updated. Once that is done, we should
> > be able to add a functional 64-bit gettimeofday/settimeofday syscall
> > pair. While I definitely agree this is one of the most basic things to
> > have, it's also not an area of the kernel that is easy to change.
> 
> 64-bit clock_gettime / clock_settime instead of gettimeofday / 
> settimeofday should avoid the need for the kernel to have a 64-bit version 
> of struct timeval.  (Userspace 64-bit gettimeofday / settimeofday would 
> need to use a combination of the syscalls if the tz pointer is non-NULL.)

Yes, that's what I meant.

	Arnd

Re: [RFC 00/32] making inode time stamps y2038 ready

[Dave Chinner]

On Tue, Jun 03, 2014 at 04:22:19PM +0200, Arnd Bergmann wrote:
> On Monday 02 June 2014 14:57:26 H. Peter Anvin wrote:
> > On 06/02/2014 12:55 PM, Arnd Bergmann wrote:
> The possible uses I can see for non-ktime_t types in the kernel are:
> * inodes need 96 bit timestamps to represent the full range of values
>   that can be stored in a file system, you made a convincing argument
>   for that. Almost everything else can fit into 64 bit on a 32-bit
>   kernel, in theory also on a 64-bit kernel if we want that.

Just ot be pedantic, inodes don't *need* 96 bit timestamps - some
filesystems can *support up to* 96 bit timestamps. If the kernel
only supports 64 bit timestamps and that's all the kernel can
represent, then the upper bits of the 96 bit on-disk inode
timestamps simply remain zero.

If you move the filesystem between kernels with different time
ranges, then the filesystem needs to be able to tell the kernel what
it's supported range is.  This is where having the VFS limit the
range of supported timestamps is important: the limit is the
min(kernel range, filesystem range). This allows the filesystems
to be indepenent of the kernel time representation, and the kernel
to be independent of the physical filesystem time encoding....

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com

Re: [RFC 00/32] making inode time stamps y2038 ready

[Arnd Bergmann]

On Tuesday 03 June 2014, Dave Chinner wrote:
> On Tue, Jun 03, 2014 at 04:22:19PM +0200, Arnd Bergmann wrote:
> > On Monday 02 June 2014 14:57:26 H. Peter Anvin wrote:
> > > On 06/02/2014 12:55 PM, Arnd Bergmann wrote:
> > The possible uses I can see for non-ktime_t types in the kernel are:
> > * inodes need 96 bit timestamps to represent the full range of values
> >   that can be stored in a file system, you made a convincing argument
> >   for that. Almost everything else can fit into 64 bit on a 32-bit
> >   kernel, in theory also on a 64-bit kernel if we want that.
> 
> Just ot be pedantic, inodes don't need 96 bit timestamps - some
> filesystems can *support up to* 96 bit timestamps. If the kernel
> only supports 64 bit timestamps and that's all the kernel can
> represent, then the upper bits of the 96 bit on-disk inode
> timestamps simply remain zero.

I meant the reverse: since we have file systems that can store
96-bit timestamps when using 64-bit kernels, we need to extend
32-bit kernels to have the same internal representation so we
can actually read those file systems correctly.

> If you move the filesystem between kernels with different time
> ranges, then the filesystem needs to be able to tell the kernel what
> it's supported range is.  This is where having the VFS limit the
> range of supported timestamps is important: the limit is the
> min(kernel range, filesystem range). This allows the filesystems
> to be indepenent of the kernel time representation, and the kernel
> to be independent of the physical filesystem time encoding....

I agree it makes sense to let the kernel know about the limits
of the file system it accesses, but for the reverse, we're probably
better off just making the kernel representation large enough (i.e.
96 bits) so it can work with any known file system. We need another
check at the user space boundary to turn that into a value that the
user can understand, but that's another problem.

	Arnd

Re: [RFC 00/32] making inode time stamps y2038 ready

[Arnd Bergmann]

On Monday 02 June 2014, Joseph S. Myers wrote:
> On Mon, 2 Jun 2014, Arnd Bergmann wrote:
> 
> > Ok. Sorry about missing linux-api, I confused it with linux-arch, which
> > may not be as relevant here, except for the one question whether we
> > actually want to have the new ABI on all 32-bit architectures or only
> > as an opt-in for those that expect to stay around for another 24 years.
> 
> For glibc I think it will make the most sense to add the support for 
> 64-bit time_t across all architectures that currently have 32-bit time_t 
> (with the new interfaces having fallback support to implementation in 
> terms of the 32-bit kernel interfaces, if the 64-bit syscalls are 
> unavailable either at runtime or in the kernel headers against which glibc 
> is compiled - this fallback code will of course need to check for overflow 
> when passing a time value to the kernel, hopefully with error handling 
> consistent with whatever the kernel ends up doing when a filesystem can't 
> support a timestamp).  If some architectures don't provide the new 
> interfaces in the kernel then that will mean the fallback code in glibc 
> can't be removed until glibc support for those architectures is removed 
> (as opposed to removing it when glibc no longer supports kernels predating 
> the kernel support).

Ok, that's a good reason to just provide the new interfaces on all
architectures right away. Thanks for the insight!

	Arnd

Re: [RFC 00/32] making inode time stamps y2038 ready

[Nicolas Pitre]

On Wed, 4 Jun 2014, Arnd Bergmann wrote:

> On Tuesday 03 June 2014, Dave Chinner wrote:
> > Just ot be pedantic, inodes don't need 96 bit timestamps - some
> > filesystems can *support up to* 96 bit timestamps. If the kernel
> > only supports 64 bit timestamps and that's all the kernel can
> > represent, then the upper bits of the 96 bit on-disk inode
> > timestamps simply remain zero.
> 
> I meant the reverse: since we have file systems that can store
> 96-bit timestamps when using 64-bit kernels, we need to extend
> 32-bit kernels to have the same internal representation so we
> can actually read those file systems correctly.
> 
> > If you move the filesystem between kernels with different time
> > ranges, then the filesystem needs to be able to tell the kernel what
> > it's supported range is.  This is where having the VFS limit the
> > range of supported timestamps is important: the limit is the
> > min(kernel range, filesystem range). This allows the filesystems
> > to be indepenent of the kernel time representation, and the kernel
> > to be independent of the physical filesystem time encoding....
> 
> I agree it makes sense to let the kernel know about the limits
> of the file system it accesses, but for the reverse, we're probably
> better off just making the kernel representation large enough (i.e.
> 96 bits) so it can work with any known file system.

Depends...  96 bit handling may get prohibitive on 32-bit archs.

The important point here is for the kernel to be able to represent the 
time _range_ used by any known filesystem, not necessarily the time 
_precision_.

For example, a 64 bit representation can be made of 40 bits for seconds 
spanning 34865 years, and 24 bits for fractional seconds providing 
precision down to 60 nanosecs.  That ought to be plenty good on 32 bit 
systems while still being cheap to handle.


Nicolas

Re: [RFC 00/32] making inode time stamps y2038 ready

[Arnd Bergmann]

On Wednesday 04 June 2014 13:30:32 Nicolas Pitre wrote:
> On Wed, 4 Jun 2014, Arnd Bergmann wrote:
> 
> > On Tuesday 03 June 2014, Dave Chinner wrote:
> > > Just ot be pedantic, inodes don't need 96 bit timestamps - some
> > > filesystems can *support up to* 96 bit timestamps. If the kernel
> > > only supports 64 bit timestamps and that's all the kernel can
> > > represent, then the upper bits of the 96 bit on-disk inode
> > > timestamps simply remain zero.
> > 
> > I meant the reverse: since we have file systems that can store
> > 96-bit timestamps when using 64-bit kernels, we need to extend
> > 32-bit kernels to have the same internal representation so we
> > can actually read those file systems correctly.
> > 
> > > If you move the filesystem between kernels with different time
> > > ranges, then the filesystem needs to be able to tell the kernel what
> > > it's supported range is.  This is where having the VFS limit the
> > > range of supported timestamps is important: the limit is the
> > > min(kernel range, filesystem range). This allows the filesystems
> > > to be indepenent of the kernel time representation, and the kernel
> > > to be independent of the physical filesystem time encoding....
> > 
> > I agree it makes sense to let the kernel know about the limits
> > of the file system it accesses, but for the reverse, we're probably
> > better off just making the kernel representation large enough (i.e.
> > 96 bits) so it can work with any known file system.
> 
> Depends...  96 bit handling may get prohibitive on 32-bit archs.
> 
> The important point here is for the kernel to be able to represent the 
> time _range_ used by any known filesystem, not necessarily the time 
> _precision_.
> 
> For example, a 64 bit representation can be made of 40 bits for seconds 
> spanning 34865 years, and 24 bits for fractional seconds providing 
> precision down to 60 nanosecs.  That ought to be plenty good on 32 bit 
> systems while still being cheap to handle.

I have checked earlier that we don't do any computation on inode
time stamps in common code, we just pass them around, so there is
very little runtime overhead. There is a small bit of space overhead
(12 byte) per inode, but that structure is already on the order of
500 bytes.

For other timekeeping stuff in the kernel, I agree that using some
64-bit representation (nanoseconds, 32/32 unsigned seconds/nanoseconds,
...) has advantages, that's exactly the point I was making earlier
against simply extending the internal time_t/timespec to 64-bit
seconds for everything.

	Arnd

Re: [RFC 00/32] making inode time stamps y2038 ready

[H. Peter Anvin]

On 06/04/2014 12:24 PM, Arnd Bergmann wrote:
> 
> For other timekeeping stuff in the kernel, I agree that using some
> 64-bit representation (nanoseconds, 32/32 unsigned seconds/nanoseconds,
> ...) has advantages, that's exactly the point I was making earlier
> against simply extending the internal time_t/timespec to 64-bit
> seconds for everything.
> 

How much of a performance issue is it to make time_t 64 bits, and for
the bits there are, how hard are they to fix?

	-hpa

Re: [RFC 00/32] making inode time stamps y2038 ready

[Arnd Bergmann]

On Wednesday 04 June 2014 17:10:24 H. Peter Anvin wrote:
> On 06/04/2014 12:24 PM, Arnd Bergmann wrote:
> > 
> > For other timekeeping stuff in the kernel, I agree that using some
> > 64-bit representation (nanoseconds, 32/32 unsigned seconds/nanoseconds,
> > ...) has advantages, that's exactly the point I was making earlier
> > against simply extending the internal time_t/timespec to 64-bit
> > seconds for everything.
> > 
> 
> How much of a performance issue is it to make time_t 64 bits, and for
> the bits there are, how hard are they to fix?

Probably very little overhead for most uses, it's more the regression
potential in the less common parts of the kernel I'm worried about.

There is a significant but not overwhelming number of uses of the
main problematic types in the kernel:

arnd@wuerfel:~/arm-soc$ git grep -wl time_t | wc
    188     188    5566
arnd@wuerfel:~/arm-soc$ git grep -wl timeval | wc
    320     320   10353
arnd@wuerfel:~/arm-soc$ git grep -wl timespec | wc
    406     406   10886

I believe we have to audit all of them anyway if we want to change
the kernel to less problematic types and introduce new user
interfaces.

IMHO this work is helped if we change the uses to a new type
as we find the problems. This lets us do the work one subsystem
at a time and avoid accidental ABI changes. I don't care much what
type that will be, and having a 96-bit type will certainly work
well in a lot of cases, but I don't see a strong reason to use
that over other types, especially when they can be more efficient.

	Arnd