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

Gabriel Krisman Bertazi
2024-01-23T14:53:28Z

Tony Solomonik <tony.solomonik@gmail.com> writes:

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

This need to be Cc'ed to the VFS maintainers and appropriated lists.
Also, you need a signed-off-by line and cover letter.

Take a look at:

https://www.kernel.org/doc/html/v6.7/process/submitting-patches.html

>
> __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;

Just return directly here. No point in jumping to 'out' just to return
immediately.

>
> error = -EINVAL;
> /* Cannot ftruncate over 2^31 bytes without large file support */
> if (small && length > MAX_NON_LFS)
> - goto out_putf;
> + goto out;

likewise for the others..

>
> 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:
> return error;

Same here.

> 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)

--
Gabriel Krisman Bertazi