Re: [PATCH v8 1/2] Add do_ftruncate that truncates a struct file

[Christian Brauner <brauner@kernel.org>]

On Mon, Jan 29, 2024 at 05:15:06PM +0200, Tony Solomonik wrote:
> 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@gmail.com>
> ---
>  fs/internal.h |  1 +
>  fs/open.c     | 52 ++++++++++++++++++++++++++++-----------------------
>  2 files changed, 30 insertions(+), 23 deletions(-)
> 
> diff --git a/fs/internal.h b/fs/internal.h
> index 58e43341aebf..d35b1c05cf6d 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);
>  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..6d608ff4a3f7 100644
> --- a/fs/open.c
> +++ b/fs/open.c
> @@ -154,49 +154,55 @@ 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)
>  {
>  	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;
> +
> +	/* 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;

Why is the O_LARGEFILE handling not needed when used from io_uring?