fs: introduce inode operation ->update_time

Btrfs has to make sure we have space to allocate new blocks in order to modify
the inode, so updating time can fail.  We've gotten around this by having our
own file_update_time but this is kind of a pain, and Christoph has indicated he
would like to make xfs do something different with atime updates.  So introduce
->update_time, where we will deal with i_version an a/m/c time updates and
indicate which changes need to be made.  The normal version just does what it
has always done, updates the time and marks the inode dirty, and then
filesystems can choose to do something different.

I've gone through all of the users of file_update_time and made them check for
errors with the exception of the fault code since it's complicated and I wasn't
quite sure what to do there, also Jan is going to be pushing the file time
updates into page_mkwrite for those who have it so that should satisfy btrfs and
make it not a big deal to check the file_update_time() return code in the
generic fault path. Thanks,

Signed-off-by: Josef Bacik <josef@redhat.com>

2 files changed, 7 insertions, 0 deletions

diff --git a/Documentation/filesystems/Locking b/Documentation/filesystems/Locking
index 4fca82e5276e..d5a269a51a9e 100644
--- a/Documentation/filesystems/Locking
+++ b/Documentation/filesystems/Locking
@@ -62,6 +62,7 @@ ata *);
         int (*removexattr) (struct dentry *, const char *);
         void (*truncate_range)(struct inode *, loff_t, loff_t);
         int (*fiemap)(struct inode *, struct fiemap_extent_info *, u64 start, u64 len);
+        void (*update_time)(struct inode *, struct timespec *, int);
 
 locking rules:
         all may block
@@ -89,6 +90,8 @@ listxattr:	no
 removexattr:    yes
 truncate_range: yes
 fiemap:         no
+update_time:    no
+
         Additionally, ->rmdir(), ->unlink() and ->rename() have ->i_mutex on
 victim.
         cross-directory ->rename() has (per-superblock) ->s_vfs_rename_sem.
diff --git a/Documentation/filesystems/vfs.txt b/Documentation/filesystems/vfs.txt
index 0d0492028082..b2aa722e5ea2 100644
--- a/Documentation/filesystems/vfs.txt
+++ b/Documentation/filesystems/vfs.txt
@@ -364,6 +364,7 @@ struct inode_operations {
         ssize_t (*listxattr) (struct dentry *, char *, size_t);
         int (*removexattr) (struct dentry *, const char *);
         void (*truncate_range)(struct inode *, loff_t, loff_t);
+        void (*update_time)(struct inode *, struct timespec *, int);
 };
 
 Again, all methods are called without any locks being held, unless
@@ -475,6 +476,9 @@ otherwise noted.
   truncate_range: a method provided by the underlying filesystem to truncate a
         range of blocks , i.e. punch a hole somewhere in a file.
 
+  update_time: called by the VFS to update a specific time or the i_version of
+        an inode.  If this is not defined the VFS will update the inode itself
+        and call mark_inode_dirty_sync.
 
 The Address Space Object
 ========================