Re: [PATCH v2 1/2] Add __do_ftruncate that truncates a struct file*

[Jens Axboe <axboe@kernel.dk>]

On 1/23/24 4:33 AM, Tony Solomonik wrote:
> do_sys_ftruncate receives a file descriptor, fgets the struct file*, and
> finally actually truncates the file.
> 
> __do_ftruncate allows for truncating a file without fgets.
> ---
>  fs/open.c                | 52 ++++++++++++++++++++++++----------------
>  include/linux/syscalls.h |  2 ++
>  2 files changed, 33 insertions(+), 21 deletions(-)
> 
> diff --git a/fs/open.c b/fs/open.c
> index 02dc608d40d8..b32ac430666c 100644
> --- a/fs/open.c
> +++ b/fs/open.c
> @@ -154,47 +154,57 @@ 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;
> -	struct fd f;
>  	int error;
>  
> -	error = -EINVAL;
> -	if (length < 0)
> -		goto out;
> -	error = -EBADF;
> -	f = fdget(fd);
> -	if (!f.file)
> -		goto out;
> -
>  	/* explicitly opened as large or we are on 64-bit box */
> -	if (f.file->f_flags & O_LARGEFILE)
> +	if (file->f_flags & O_LARGEFILE)
>  		small = 0;
>  
> -	dentry = f.file->f_path.dentry;
> +	dentry = 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;
> +	if (!S_ISREG(inode->i_mode) || !(file->f_mode & FMODE_WRITE))
> +		goto out;
>  
>  	error = -EINVAL;
>  	/* Cannot ftruncate over 2^31 bytes without large file support */
>  	if (small && length > MAX_NON_LFS)
> -		goto out_putf;
> +		goto out;
>  
>  	error = -EPERM;
>  	/* Check IS_APPEND on real upper inode */
> -	if (IS_APPEND(file_inode(f.file)))
> -		goto out_putf;
> +	if (IS_APPEND(file_inode(file)))
> +		goto out;
>  	sb_start_write(inode->i_sb);
> -	error = security_file_truncate(f.file);
> +	error = security_file_truncate(file);
>  	if (!error)
> -		error = do_truncate(file_mnt_idmap(f.file), dentry, length,
> -				    ATTR_MTIME | ATTR_CTIME, f.file);
> +		error = do_truncate(file_mnt_idmap(file), dentry, length,
> +				    ATTR_MTIME | ATTR_CTIME, file);
>  	sb_end_write(inode->i_sb);
> -out_putf:
> +
> +out:
> +  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;
> +	f = fdget(fd);
> +	if (!f.file)
> +		goto out;
> +
> +	error = __do_ftruncate(f.file, length, small);
> +
>  	fdput(f);
>  out:

Same comments as Gabriel for the out label, just return error.

> diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
> index fd9d12de7e92..e8c56986e751 100644
> --- a/include/linux/syscalls.h
> +++ b/include/linux/syscalls.h
> @@ -1229,6 +1229,8 @@ static inline long ksys_lchown(const char __user *filename, uid_t user,
>  			     AT_SYMLINK_NOFOLLOW);
>  }
>  
> +extern long __do_ftruncate(struct file *file, loff_t length, int small);
> +
>  extern long do_sys_ftruncate(unsigned int fd, loff_t length, int small);
>  
>  static inline long ksys_ftruncate(unsigned int fd, loff_t length)

This should go in fs/internal.h, it's not a syscall related thing.

-- 
Jens Axboe