Re: [PATCH v7 1/7] VFS: Introduce new O_DENY* open flags

[Pavel Shilovsky]

2014/1/17 One Thousand Gnomes <gnomes(a)lxorguk.ukuu.org.uk>:
> > +#define ESHAREDENIED 258     /* File is locked with a sharelock */
>
> Have you prepared C library patches to match this ?

I don't have it for now.
> (and why not just use EPERM, it has the meaning you want already)

We need to determine if we have a share reservation error to map it
accurately in file servers and wine.
> > + * Check to see if there's a share_reservation conflict. LOCK_READ/LOCK_WRITE
> > + * tell us whether the reservation allows other readers and writers.
> > + */
> > +static int
> > +locks_mand_conflict(struct file_lock *caller_fl, struct file_lock *sys_fl)
> > +{
>
> Shouldn't this also check for CAP_SYS_DAC or some similar permission so
> that root can override such a mess (eg to fix full disks in an
> emergency) ?

May be it's better to let root an ability to remount the system
without sharelock mount option and then fix an emergency?
> > +
> > +     /*
> > +      * For sharelock mounts if a file was created but not opened, we need
> > +      * to keep parent i_mutex until we finish the open to prevent races when
> > +      * somebody opens newly created by us file and locks it with a sharelock
> > +      * before we open it.
> > +      */
> > +     if (IS_SHARELOCK(dir->d_inode) && error > 0 && *opened & FILE_CREATED) {
> > +             /* Don't check for write permission, don't truncate */
> > +             open_flag &= ~O_TRUNC;
> > +             will_truncate = false;
> > +             acc_mode = MAY_OPEN;
> > +             path_to_nameidata(path, nd);
> > +
> > +             error = may_open(&nd->path, acc_mode, open_flag);
> > +             if (error) {
> > +                     mutex_unlock(&dir->d_inode->i_mutex);
> > +                     goto out;
> > +             }
> > +             file->f_path.mnt = nd->path.mnt;
> > +             error = finish_open(file, nd->path.dentry, NULL, opened);
> > +             if (error) {
> > +                     mutex_unlock(&dir->d_inode->i_mutex);
> > +                     if (error == -EOPENSTALE)
> > +                             goto stale_open;
> > +                     goto out;
> > +             }
> > +             error = sharelock_lock_file(file);
> > +             mutex_unlock(&dir->d_inode->i_mutex);
> > +             if (error)
> > +                     goto exit_fput;
> > +             goto opened;
> > +     }
> > +
> >       mutex_unlock(&dir->d_inode->i_mutex);
>
> What stops the file system changing mount flags via a remount between
> these two ?

Nothing, but it doesn't bring problems here: if the first IS_SHARELOCK
condition is true, we don't get into the second (see 'goto opened').
> > if (error <= 0) {
> > @@ -3034,6 +3073,18 @@ finish_open_created:
> >                       goto stale_open;
> >               goto out;
> >       }
> > +
> > +     if (IS_SHARELOCK(dir->d_inode)) {
> > +             /*
> > +              * Lock parent i_mutex to prevent races with sharelocks on
> > +              * newly created files.
> > +              */
> > +             mutex_lock(&dir->d_inode->i_mutex);
> > +             error = sharelock_lock_file(file);
> > +             mutex_unlock(&dir->d_inode->i_mutex);
> > +             if (error)
> > +                     goto exit_fput;
> > +     }
> >  opened:
>
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-- 
Best regards,
Pavel Shilovsky.