[patch] fix truncate inode time modification breakage

[Nick Piggin <npiggin@suse.de>]

It appears that I've broken inode time modifications on tmpfs/ext2.
While ftruncate always updates these attributes, truncate must not
unless size is changed. I hadn't actually understood that until
Christoph told me.

Confusion is increased because other filesystems get this wrong.
Those without ->setattr or ->truncate get it wrong by default.
Others appear to have problems too.

I haven't gone through many yet, but is there any reason not to
just do it in the vfs?

---
 fs/ext2/inode.c       |    1 -
 fs/open.c             |    3 +++
 fs/ramfs/file-nommu.c |    5 -----
 mm/shmem.c            |    5 +++--
 4 files changed, 6 insertions(+), 8 deletions(-)

Index: linux-2.6/fs/ext2/inode.c
===================================================================
--- linux-2.6.orig/fs/ext2/inode.c
+++ linux-2.6/fs/ext2/inode.c
@@ -1203,7 +1203,6 @@ int ext2_setsize(struct inode *inode, lo
 
 	__ext2_truncate_blocks(inode, newsize);
 
-	inode->i_mtime = inode->i_ctime = CURRENT_TIME_SEC;
 	if (inode_needs_sync(inode)) {
 		sync_mapping_buffers(inode->i_mapping);
 		ext2_sync_inode (inode);
Index: linux-2.6/fs/open.c
===================================================================
--- linux-2.6.orig/fs/open.c
+++ linux-2.6/fs/open.c
@@ -55,6 +55,9 @@ int do_truncate(struct dentry *dentry, l
 		newattrs.ia_valid |= ret | ATTR_FORCE;
 
 	mutex_lock(&dentry->d_inode->i_mutex);
+	/* Unlike ftruncate, truncate only updates times when size changes */
+	if (length != dentry->d_inode->i_size)
+		newattrs.ia_valid |= ATTR_MTIME|ATTR_CTIME;
 	ret = notify_change(dentry, &newattrs);
 	mutex_unlock(&dentry->d_inode->i_mutex);
 	return ret;
Index: linux-2.6/mm/shmem.c
===================================================================
--- linux-2.6.orig/mm/shmem.c
+++ linux-2.6/mm/shmem.c
@@ -764,10 +764,11 @@ done2:
 static int shmem_notify_change(struct dentry *dentry, struct iattr *attr)
 {
 	struct inode *inode = dentry->d_inode;
+	loff_t newsize = attr->ia_size;
 	int error;
 
-	if (S_ISREG(inode->i_mode) && (attr->ia_valid & ATTR_SIZE)) {
-		loff_t newsize = attr->ia_size;
+	if (S_ISREG(inode->i_mode) && (attr->ia_valid & ATTR_SIZE) &&
+						newsize != inode->i_size) {
 		struct page *page = NULL;
 
 		if (newsize < inode->i_size) {
Index: linux-2.6/fs/ramfs/file-nommu.c
===================================================================
--- linux-2.6.orig/fs/ramfs/file-nommu.c
+++ linux-2.6/fs/ramfs/file-nommu.c
@@ -175,11 +175,6 @@ static int ramfs_nommu_setattr(struct de
 			ret = ramfs_nommu_resize(inode, ia->ia_size, size);
 			if (ret < 0 || ia->ia_valid == ATTR_SIZE)
 				goto out;
-		} else {
-			/* we skipped the truncate but must still update
-			 * timestamps
-			 */
-			ia->ia_valid |= ATTR_MTIME|ATTR_CTIME;
 		}
 	}