[PATCH v6 1/2] Add do_ftruncate that truncates a struct file

[Tony Solomonik <tony.solomonik@xxxxxxxxx>]

do_sys_ftruncate receives a file descriptor, fgets the struct file, and
finally actually truncates the file.

do_ftruncate allows for passing in a file directly, with the caller
already holding a reference to it.

Signed-off-by: Tony Solomonik <tony.solomonik@xxxxxxxxx>
---
 fs/internal.h |  1 +
 fs/open.c     | 57 +++++++++++++++++++++++++++------------------------
 2 files changed, 31 insertions(+), 27 deletions(-)

diff --git a/fs/internal.h b/fs/internal.h
index 58e43341aebf..bb3df26a9a13 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -182,6 +182,7 @@ extern struct open_how build_open_how(int flags, umode_t mode);
 extern int build_open_flags(const struct open_how *how, struct open_flags *op);
 extern struct file *__close_fd_get_file(unsigned int fd);
 
+long do_ftruncate(struct file *file, loff_t length, int small);
 long do_sys_ftruncate(unsigned int fd, loff_t length, int small);
 int chmod_common(const struct path *path, umode_t mode);
 int do_fchownat(int dfd, const char __user *filename, uid_t user, gid_t group,
diff --git a/fs/open.c b/fs/open.c
index 02dc608d40d8..77db60c416db 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -154,49 +154,52 @@ COMPAT_SYSCALL_DEFINE2(truncate, const char __user *, path, compat_off_t, length
 }
 #endif
 
-long do_sys_ftruncate(unsigned int fd, loff_t length, int small)
+long do_ftruncate(struct file *file, loff_t length, int small)
 {
 	struct inode *inode;
 	struct dentry *dentry;
+	int error;
+
+	dentry = file->f_path.dentry;
+	inode = dentry->d_inode;
+	if (!S_ISREG(inode->i_mode) || !(file->f_mode & FMODE_WRITE))
+		return -EINVAL;
+
+	/* Cannot ftruncate over 2^31 bytes without large file support */
+	if (small && length > MAX_NON_LFS)
+		return -EINVAL;
+
+	/* Check IS_APPEND on real upper inode */
+	if (IS_APPEND(file_inode(file)))
+		return -EPERM;
+	sb_start_write(inode->i_sb);
+	error = security_file_truncate(file);
+	if (!error)
+		error = do_truncate(file_mnt_idmap(file), dentry, length,
+				    ATTR_MTIME | ATTR_CTIME, file);
+	sb_end_write(inode->i_sb);
+
+  return error;
+}
+
+long do_sys_ftruncate(unsigned int fd, loff_t length, int small)
+{
 	struct fd f;
 	int error;
 
-	error = -EINVAL;
 	if (length < 0)
-		goto out;
-	error = -EBADF;
+		return -EINVAL;
 	f = fdget(fd);
 	if (!f.file)
-		goto out;
+		return -EBADF;
 
 	/* explicitly opened as large or we are on 64-bit box */
 	if (f.file->f_flags & O_LARGEFILE)
 		small = 0;
 
-	dentry = f.file->f_path.dentry;
-	inode = dentry->d_inode;
-	error = -EINVAL;
-	if (!S_ISREG(inode->i_mode) || !(f.file->f_mode & FMODE_WRITE))
-		goto out_putf;
+	error = do_ftruncate(f.file, length, small);
 
-	error = -EINVAL;
-	/* Cannot ftruncate over 2^31 bytes without large file support */
-	if (small && length > MAX_NON_LFS)
-		goto out_putf;
-
-	error = -EPERM;
-	/* Check IS_APPEND on real upper inode */
-	if (IS_APPEND(file_inode(f.file)))
-		goto out_putf;
-	sb_start_write(inode->i_sb);
-	error = security_file_truncate(f.file);
-	if (!error)
-		error = do_truncate(file_mnt_idmap(f.file), dentry, length,
-				    ATTR_MTIME | ATTR_CTIME, f.file);
-	sb_end_write(inode->i_sb);
-out_putf:
 	fdput(f);
-out:
 	return error;
 }
 
-- 
2.34.1