[PATCH v3] vfs: Add support to document max and min inode times

[PATCH v3] vfs: Add support to document max and min inode times

[Deepa Dinamani]

This is a preparation patch to add range checking for inode
timestamps.

Extend struct super_block to include information about the max
and min inode times each filesystem can hold. These are dependent
on the on-disk format of filesystems.

These range checks will be used to clamp timestamps to filesystem
allowed ranges.

Individual filesystems do not have the same on disk format as
the in memory inodes. Range checking and clamping times assigned
to inodes will help keep in memory and on-disk timestamps to be
in sync.

Another series will initialize these fields to appropriate values for
every filesystem.

The fields are not used by vfs yet.
The exact policy and behavior will be decided in a separate patch.

The original idea for the feature comes from the discussion:
https://lkml.org/lkml/2014/5/30/669

Signed-off-by: Deepa Dinamani <deepa.kernel@gmail.com>
---
Changes from v2:
* Only add fields in the structure.
* All other logic moved to a different patch.

Changes from v1:
* Delete INVALID macros, use VFS_TIME macros directly.
* Add comment in alloc_super() to explain range checking.
* Reword the commit text to reflect the above.

include/linux/fs.h | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 5cef14a..2ceed39 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1374,7 +1374,14 @@ struct super_block {
 
 	/* Granularity of c/m/atime in ns.
 	   Cannot be worse than a second */
-	u32		   s_time_gran;
+	u32		s_time_gran;
+
+	/*
+	 * Max and min values for timestamps
+	 * according to the range supported by filesystems.
+	 */
+	time64_t	s_time_min;
+	time64_t	s_time_max;
 
 	/*
 	 * The next field is for VFS *only*. No filesystems have any business
-- 
1.9.1