Re: Change in NFS client behavior

[Trond Myklebust]

to den 01.09.2005 Klokka 21:07 (-0700) skreiv Andrew Morton:

> Of course.  But with your patch, the optimisation in inode_setattr() is
> redundant (except for O_TRUNC, perhaps).

Sure. The other problem is that the test is made before the i_sem is
grabbed. OK, so how about the appended patch instead?

Cheers,
  Trond

VFS/NFS: Fix up behaviour w.r.t. truncate() and open(O_TRUNC)

 POSIX and the SUSv3 specify that open(O_TRUNC) should always bump ctime/mtime
 whereas truncate() should only do so if the file size actually changes.

 Fix the behaviour of NFS, which currently is broken w.r.t. open(), and fix
 the VFS truncate() so that it no enforces the POSIX rules.

 Signed-off-by: Trond Myklebust <Trond.Myklebust@xxxxxxxxxx>
---
 attr.c      |   14 +++-----------
 nfs/inode.c |    5 -----
 open.c      |   25 +++++++++++++++++++++++--
 3 files changed, 26 insertions(+), 18 deletions(-)

Index: linux-2.6.13/fs/nfs/inode.c
===================================================================
--- linux-2.6.13.orig/fs/nfs/inode.c
+++ linux-2.6.13/fs/nfs/inode.c
@@ -833,11 +833,6 @@ nfs_setattr(struct dentry *dentry, struc
 	struct nfs_fattr fattr;
 	int error;
 
-	if (attr->ia_valid & ATTR_SIZE) {
-		if (!S_ISREG(inode->i_mode) || attr->ia_size == i_size_read(inode))
-			attr->ia_valid &= ~ATTR_SIZE;
-	}
-
 	/* Optimization: if the end result is no change, don't RPC */
 	attr->ia_valid &= NFS_VALID_ATTRS;
 	if (attr->ia_valid == 0)
Index: linux-2.6.13/fs/open.c
===================================================================
--- linux-2.6.13.orig/fs/open.c
+++ linux-2.6.13/fs/open.c
@@ -206,11 +206,32 @@ int do_truncate(struct dentry *dentry, l
 	newattrs.ia_valid = ATTR_SIZE | ATTR_CTIME;
 
 	down(&dentry->d_inode->i_sem);
+	/* This should be used for open(O_TRUNC) and functions that need to
+	 * set mtime/ctime whether or not the size changes
+	 */
+	if (length == i_size_read(dentry->d_inode))
+		newattrs.ia_valid &= ~ATTR_SIZE;
 	err = notify_change(dentry, &newattrs);
 	up(&dentry->d_inode->i_sem);
 	return err;
 }
 
+static int do_posix_truncate(struct dentry *dentry, loff_t length)
+{
+	int err = 0;
+	struct iattr newattrs;
+
+	newattrs.ia_size = length;
+	newattrs.ia_valid = ATTR_SIZE;
+
+	down(&dentry->d_inode->i_sem);
+	/* In SuS/Posix lore, truncate to the current file size is a no-op */
+	if (length != i_size_read(dentry->d_inode))
+		err = do_truncate(dentry, length);
+	up(&dentry->d_inode->i_sem);
+	return err;
+}
+
 static inline long do_sys_truncate(const char __user * path, loff_t length)
 {
 	struct nameidata nd;
@@ -261,7 +282,7 @@ static inline long do_sys_truncate(const
 	error = locks_verify_truncate(inode, NULL, length);
 	if (!error) {
 		DQUOT_INIT(inode);
-		error = do_truncate(nd.dentry, length);
+		error = do_posix_truncate(nd.dentry, length);
 	}
 	put_write_access(inode);
 
@@ -313,7 +334,7 @@ static inline long do_sys_ftruncate(unsi
 
 	error = locks_verify_truncate(inode, file, length);
 	if (!error)
-		error = do_truncate(dentry, length);
+		error = do_posix_truncate(dentry, length);
 out_putf:
 	fput(file);
 out:
Index: linux-2.6.13/fs/attr.c
===================================================================
--- linux-2.6.13.orig/fs/attr.c
+++ linux-2.6.13/fs/attr.c
@@ -70,17 +70,9 @@ int inode_setattr(struct inode * inode, 
 	int error = 0;
 
 	if (ia_valid & ATTR_SIZE) {
-		if (attr->ia_size != i_size_read(inode)) {
-			error = vmtruncate(inode, attr->ia_size);
-			if (error || (ia_valid == ATTR_SIZE))
-				goto out;
-		} else {
-			/*
-			 * We skipped the truncate but must still update
-			 * timestamps
-			 */
-			ia_valid |= ATTR_MTIME|ATTR_CTIME;
-		}
+		error = vmtruncate(inode, attr->ia_size);
+		if (error || (ia_valid == ATTR_SIZE))
+			goto out;
 	}
 
 	if (ia_valid & ATTR_UID)