linux-kernel - Re: [PATCH v2 21/35] ovl: add reflink/copyfile/dedup support

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Message-ID: <CAJfpegu_iYLUeYU_OgZryFmCqa_a9MHt32nnsu7h_+JVXJ2d4w@mail.gmail.com>
Date:   Tue, 8 May 2018 16:13:01 +0200
From:   Miklos Szeredi <miklos@...redi.hu>
To:     "Darrick J. Wong" <darrick.wong@...cle.com>
Cc:     Miklos Szeredi <mszeredi@...hat.com>,
        overlayfs <linux-unionfs@...r.kernel.org>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 21/35] ovl: add reflink/copyfile/dedup support

On Mon, May 7, 2018 at 10:43 PM, Darrick J. Wong
<darrick.wong@...cle.com> wrote:
> On Mon, May 07, 2018 at 10:37:53AM +0200, Miklos Szeredi wrote:
>> Since set of arguments are so similar, handle in a common helper.
>>
>> Signed-off-by: Miklos Szeredi <mszeredi@...hat.com>
>> ---
>>  fs/overlayfs/file.c | 88 +++++++++++++++++++++++++++++++++++++++++++++++++++++
>>  1 file changed, 88 insertions(+)
>>
>> diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c
>> index ce871a15e185..2ac95c95e8e6 100644
>> --- a/fs/overlayfs/file.c
>> +++ b/fs/overlayfs/file.c
>> @@ -382,6 +382,90 @@ static long ovl_compat_ioctl(struct file *file, unsigned int cmd,
>>       return ovl_ioctl(file, cmd, arg);
>>  }
>>
>> +enum ovl_copyop {
>> +     OVL_COPY,
>> +     OVL_CLONE,
>> +     OVL_DEDUPE,
>> +};
>> +
>> +static s64 ovl_copyfile(struct file *file_in, loff_t pos_in,
>> +                     struct file *file_out, loff_t pos_out,
>> +                     u64 len, unsigned int flags, enum ovl_copyop op)
>> +{
>> +     struct inode *inode_out = file_inode(file_out);
>> +     struct fd real_in, real_out;
>> +     const struct cred *old_cred;
>> +     s64 ret;
>> +
>> +     ret = ovl_real_fdget(file_out, &real_out);
>> +     if (ret)
>> +             return ret;
>> +
>> +     ret = ovl_real_fdget(file_in, &real_in);
>> +     if (ret) {
>> +             fdput(real_out);
>> +             return ret;
>> +     }
>> +
>> +     old_cred = ovl_override_creds(file_inode(file_out)->i_sb);
>> +     switch (op) {
>> +     case OVL_COPY:
>> +             ret = vfs_copy_file_range(real_in.file, pos_in,
>> +                                       real_out.file, pos_out, len, flags);
>> +             break;
>> +
>> +     case OVL_CLONE:
>> +             ret = vfs_clone_file_range(real_in.file, pos_in,
>> +                                        real_out.file, pos_out, len);
>> +             break;
>> +
>> +     case OVL_DEDUPE:
>> +             ret = vfs_dedupe_file_range_one(real_in.file, pos_in,
>> +                                             real_out.file, pos_out, len);
>> +             break;
>> +     }
>> +     revert_creds(old_cred);
>> +
>> +     /* Update size */
>> +     ovl_copyattr(ovl_inode_real(inode_out), inode_out);
>> +
>> +     fdput(real_in);
>> +     fdput(real_out);
>> +
>> +     return ret;
>> +}
>> +
>> +static ssize_t ovl_copy_file_range(struct file *file_in, loff_t pos_in,
>> +                                struct file *file_out, loff_t pos_out,
>> +                                size_t len, unsigned int flags)
>> +{
>> +     return ovl_copyfile(file_in, pos_in, file_out, pos_out, len, flags,
>> +                         OVL_COPY);
>> +}
>> +
>> +static int ovl_clone_file_range(struct file *file_in, loff_t pos_in,
>> +                             struct file *file_out, loff_t pos_out, u64 len)
>> +{
>> +     return ovl_copyfile(file_in, pos_in, file_out, pos_out, len, 0,
>> +                         OVL_CLONE);
>> +}
>> +
>> +static s64 ovl_dedupe_file_range(struct file *file_in, loff_t pos_in,
>> +                              struct file *file_out, loff_t pos_out,
>> +                              u64 len)
>> +{
>> +     /*
>> +      * Don't copy up because of a dedupe request, this wouldn't make sense
>> +      * most of the time (data would be duplicated instead of deduplicated).
>> +      */
>> +     if (!ovl_inode_upper(file_inode(file_in)) ||
>> +         !ovl_inode_upper(file_inode(file_out)))
>> +             return -EPERM;
>
> /me wonders, why not EOPNOTSUPP?  That's what we've been using (in xfs
> anyway) for "filesystem doesn't want to let you do this".

EOPNOTSUPP might be interpreted as "this filesystem doesn't support
dedupe", even though here it's just "these two particular files don't
support dedupe".

>
> (Or I guess EXDEV, but "cross-device link not supported" might not be
> quite what you want users to see...)

Hmm, I like EPERM better.   EPERM means something like  "you can't do
this for some unspecified reason".  This is exactly the case here.

Thanks,
Miklos