linux-kernel - Re: [PATCH v7 1/7] VFS: Introduce new O

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Message-ID: <CAKywueT=JsTkNC+w-vrN0ftam7F8Eqb8DXJ0w2G4q9vnt0hVNQ@mail.gmail.com>
Date:	Mon, 20 Jan 2014 14:45:00 +0400
From:	Pavel Shilovsky <piastry@...rsoft.ru>
To:	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
Cc:	Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-cifs <linux-cifs@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Linux NFS Mailing list <linux-nfs@...r.kernel.org>,
	wine-devel@...ehq.org
Subject: Re: [PATCH v7 1/7] VFS: Introduce new O_DENY* open flags

2014/1/17 One Thousand Gnomes <gnomes@...rguk.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.
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