[PATCH] VFS: pass file pointer to filesystem from ftruncate()

This patch extends the iattr structure with a file pointer memeber, and adds
an ATTR_FILE validity flag for this member.

This is set if do_truncate() is invoked from ftruncate() or from
do_coredump().

The change is source and binary compatible.
Signed-off-by: Miklos Szeredi <miklos@szeredi.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

fs/exec.c

@@ -1511,7 +1511,7 @@ int do_coredump(long signr, int exit_code, struct pt_regs * regs)
 		goto close_fail;
 	if (!file->f_op->write)
 		goto close_fail;
-	if (do_truncate(file->f_dentry, 0) != 0)
+	if (do_truncate(file->f_dentry, 0, file) != 0)
 		goto close_fail;
 
 	retval = binfmt->core_dump(signr, regs, file);

fs/namei.c

@@ -1459,7 +1459,7 @@ int may_open(struct nameidata *nd, int acc_mode, int flag)
 		if (!error) {
 			DQUOT_INIT(inode);
 			
-			error = do_truncate(dentry, 0);
+			error = do_truncate(dentry, 0, NULL);
 		}
 		put_write_access(inode);
 		if (error)

fs/open.c

@@ -194,7 +194,7 @@ asmlinkage long sys_fstatfs64(unsigned int fd, size_t sz, struct statfs64 __user
 	return error;
 }
 
-int do_truncate(struct dentry *dentry, loff_t length)
+int do_truncate(struct dentry *dentry, loff_t length, struct file *filp)
 {
 	int err;
 	struct iattr newattrs;
@@ -205,6 +205,10 @@ int do_truncate(struct dentry *dentry, loff_t length)
 
 	newattrs.ia_size = length;
 	newattrs.ia_valid = ATTR_SIZE | ATTR_CTIME;
+	if (filp) {
+		newattrs.ia_file = filp;
+		newattrs.ia_valid |= ATTR_FILE;
+	}
 
 	down(&dentry->d_inode->i_sem);
 	err = notify_change(dentry, &newattrs);
@@ -262,7 +266,7 @@ static inline long do_sys_truncate(const char __user * path, loff_t length)
 	error = locks_verify_truncate(inode, NULL, length);
 	if (!error) {
 		DQUOT_INIT(inode);
-		error = do_truncate(nd.dentry, length);
+		error = do_truncate(nd.dentry, length, NULL);
 	}
 	put_write_access(inode);
 
@@ -314,7 +318,7 @@ static inline long do_sys_ftruncate(unsigned int fd, loff_t length, int small)
 
 	error = locks_verify_truncate(inode, file, length);
 	if (!error)
-		error = do_truncate(dentry, length);
+		error = do_truncate(dentry, length, file);
 out_putf:
 	fput(file);
 out:

include/linux/fs.h

@@ -264,6 +264,7 @@ typedef void (dio_iodone_t)(struct kiocb *iocb, loff_t offset,
 #define ATTR_ATTR_FLAG	1024
 #define ATTR_KILL_SUID	2048
 #define ATTR_KILL_SGID	4096
+#define ATTR_FILE	8192
 
 /*
  * This is the Inode Attributes structure, used for notify_change().  It
@@ -283,6 +284,13 @@ struct iattr {
 	struct timespec	ia_atime;
 	struct timespec	ia_mtime;
 	struct timespec	ia_ctime;
+
+	/*
+	 * Not an attribute, but an auxilary info for filesystems wanting to
+	 * implement an ftruncate() like method.  NOTE: filesystem should
+	 * check for (ia_valid & ATTR_FILE), and not for (ia_file != NULL).
+	 */
+	struct file	*ia_file;
 };
 
 /*
@@ -1288,7 +1296,7 @@ static inline int break_lease(struct inode *inode, unsigned int mode)
 
 /* fs/open.c */
 
-extern int do_truncate(struct dentry *, loff_t start);
+extern int do_truncate(struct dentry *, loff_t start, struct file *filp);
 extern long do_sys_open(const char __user *filename, int flags, int mode);
 extern struct file *filp_open(const char *, int, int);
 extern struct file * dentry_open(struct dentry *, struct vfsmount *, int);