linux-kernel - Re: [PATCH 3/3] fs: fat: add ioctl method in fat filesystem driver

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Date:   Mon, 29 Jan 2018 15:18:42 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     ChenGuanqiao <chen.chenchacha@...mail.com>,
        Pali Rohár <pali.rohar@...il.com>
Cc:     OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] fs: fat: add ioctl method in fat filesystem driver

+Cc: Pali, who AFAIRC is interested in FAT labeling mess.

On Wed, Jan 17, 2018 at 12:43 PM, ChenGuanqiao
<chen.chenchacha@...mail.com> wrote:

Commit message?

> Signed-off-by: ChenGuanqiao <chen.chenchacha@...mail.com>

>  #include <linux/fsnotify.h>
>  #include <linux/security.h>
>  #include <linux/falloc.h>
> +#include <linux/ctype.h>

It would be better to squeeze it to have order (to some extent) preserved.

> +static int fat_check_d_characters(char *label, unsigned long len)
> +{
> +       int i;
> +
> +       for (i = 0; i < len; ++i) {

Oy vey, unsigned long len vs. int i.

> +               switch (label[i]) {
> +               case 'a' ... 'z':
> +                       label[i] = __toupper(label[i]);
> +               case 'A' ... 'Z':
> +               case '0' ... '9':
> +               case '_':
> +               case 0x20:
> +                       continue;

I'm not sure this is best approach. And since there is no commit
message I can't be constructive.

> +               default:
> +                       return -EINVAL;
> +               }
> +       }
> +
> +       return 0;
> +}

> +static int fat_ioctl_get_volume_label(struct inode *inode,
> +                                     u8 __user *vol_label)
> +{

> +       int err = 0;

Redundant assignment.

> +       struct buffer_head *bh;
> +       struct msdos_dir_entry *de;
> +       struct super_block *sb = inode->i_sb;

Moreover, perhaps reversed tree order for the definition block?

> +
> +       inode = d_inode(sb->s_root);
> +       inode_lock_shared(inode);
> +
> +       err = fat_get_volume_label_entry(inode, &bh, &de);
> +       if (err)
> +               goto out;
> +
> +       if (copy_to_user(vol_label, de->name, MSDOS_NAME))
> +               err = -EFAULT;
> +
> +       brelse(bh);
> +out:
> +       inode_unlock_shared(inode);
> +
> +       return err;
> +}
> +

> +static int fat_ioctl_set_volume_label(struct file *file,
> +                                     u8 __user *vol_label)

Perhaps vol_label -> label, and fit one line?

> +{
> +       int err = 0;
> +       u8 label[MSDOS_NAME];
> +       struct timespec ts;
> +       struct buffer_head *boot_bh;
> +       struct buffer_head *vol_bh;
> +       struct msdos_dir_entry *de;
> +       struct fat_boot_sector *b;
> +       struct inode *inode = file_inode(file);
> +       struct super_block *sb = inode->i_sb;
> +       struct msdos_sb_info *sbi = MSDOS_SB(sb);
> +
> +       inode = d_inode(sb->s_root);
> +
> +       if (copy_from_user(label, vol_label, sizeof(label))) {
> +               err = -EFAULT;
> +               goto out;
> +       }
> +
> +       err = fat_check_d_characters(label, sizeof(label));
> +       if (err)
> +               goto out;
> +
> +       err = mnt_want_write_file(file);
> +       if (err)
> +               goto out;
> +
> +       down_write(&sb->s_umount);
> +
> +       /* Updates root directory's vol_label */
> +       err = fat_get_volume_label_entry(inode, &vol_bh, &de);
> +       ts = current_time(inode);
> +       if (err) {
> +               /* Create volume label entry */
> +               err = fat_add_volume_label_entry(inode, label, &ts);
> +               if (err)
> +                       goto out_vol_brelse;
> +       } else {
> +               /* Write to root directory */
> +               memcpy(de->name, label, sizeof(de->name));
> +               inode->i_ctime = inode->i_mtime = inode->i_atime = ts;
> +
> +               mark_buffer_dirty(vol_bh);
> +       }
> +
> +       /* Update sector's vol_label */
> +       boot_bh = sb_bread(sb, 0);
> +       if (boot_bh == NULL) {
> +               fat_msg(sb, KERN_ERR,
> +                       "unable to read boot sector to write volume label");
> +               err = -EIO;
> +               goto out_boot_brelse;
> +       }
> +
> +       b = (struct fat_boot_sector *)boot_bh->b_data;
> +       if (sbi->fat_bits == 32)
> +               memcpy(b->fat32.vol_label, label, sizeof(label));
> +       else
> +               memcpy(b->fat16.vol_label, label, sizeof(label));
> +
> +       mark_buffer_dirty(boot_bh);
> +
> +       /* Synchronize the data together */
> +       err = sync_dirty_buffer(boot_bh);
> +       if (err)
> +               goto out_boot_brelse;
> +
> +out_boot_brelse:
> +       brelse(boot_bh);
> +out_vol_brelse:
> +       brelse(vol_bh);
> +
> +       up_write(&sb->s_umount);
> +       mnt_drop_write_file(file);
> +out:
> +       return err;
> +}



-- 
With Best Regards,
Andy Shevchenko