Re: [PATCH 5/5] btrfs: add no_mtime flag to btrfs-extent-same

[Zygo Blaxell <ce3g8jdj@umail.furryterror.org>]

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On Tue, Jun 23, 2015 at 05:11:56PM +0200, David Sterba wrote:
> On Mon, Jun 22, 2015 at 03:47:42PM -0700, Mark Fasheh wrote:
> > --- a/fs/btrfs/ioctl.c
> > +++ b/fs/btrfs/ioctl.c
> > @@ -87,7 +87,8 @@ struct btrfs_ioctl_received_subvol_args_32 {
> >  
> >  
> >  static int btrfs_clone(struct inode *src, struct inode *inode,
> > -		       u64 off, u64 olen, u64 olen_aligned, u64 destoff);
> > +		       u64 off, u64 olen, u64 olen_aligned, u64 destoff,
> > +		       int no_mtime);
> 
> Please make it 'flags' and pass the verified flags directly.
> 
> >  /* Mask out flags that are inappropriate for the given type of inode. */
> >  static inline __u32 btrfs_mask_flags(umode_t mode, __u32 flags)
> > @@ -2974,7 +2975,7 @@ static int extent_same_check_offsets(struct inode *inode, u64 off, u64 *plen,
> >  }
> >  
> >  static int btrfs_extent_same(struct inode *src, u64 loff, u64 olen,
> > -			     struct inode *dst, u64 dst_loff)
> > +			     struct inode *dst, u64 dst_loff, int no_mtime)
> >  {
> >  	int ret;
> >  	u64 len = olen;
> > @@ -3054,7 +3055,8 @@ static int btrfs_extent_same(struct inode *src, u64 loff, u64 olen,
> >  	/* pass original length for comparison so we stay within i_size */
> >  	ret = btrfs_cmp_data(src, loff, dst, dst_loff, olen, &cmp);
> >  	if (ret == 0)
> > -		ret = btrfs_clone(src, dst, loff, olen, len, dst_loff);
> > +		ret = btrfs_clone(src, dst, loff, olen, len, dst_loff,
> > +				  no_mtime);
> >  
> >  	if (same_inode)
> >  		unlock_extent(&BTRFS_I(src)->io_tree, same_lock_start,
> > @@ -3088,6 +3090,7 @@ static long btrfs_ioctl_file_extent_same(struct file *file,
> >  	u64 bs = BTRFS_I(src)->root->fs_info->sb->s_blocksize;
> >  	bool is_admin = capable(CAP_SYS_ADMIN);
> >  	u16 count;
> > +	int no_mtime = 0;
> >  
> >  	if (!(file->f_mode & FMODE_READ))
> >  		return -EINVAL;
> > @@ -3139,6 +3142,12 @@ static long btrfs_ioctl_file_extent_same(struct file *file,
> >  	if (!S_ISREG(src->i_mode))
> >  		goto out;
> >  
> > +	ret = -EINVAL;
> > +	if (same->flags & ~BTRFS_SAME_FLAGS)
> > +		goto out;
> > +	if (same->flags & BTRFS_SAME_NO_MTIME)
> > +		no_mtime = 1;
> > +
> >  	/* pre-format output fields to sane values */
> >  	for (i = 0; i < count; i++) {
> >  		same->info[i].bytes_deduped = 0ULL;
> > @@ -3164,7 +3173,8 @@ static long btrfs_ioctl_file_extent_same(struct file *file,
> >  			info->status = -EACCES;
> >  		} else {
> >  			info->status = btrfs_extent_same(src, off, len, dst,
> > -							info->logical_offset);
> > +							 info->logical_offset,
> > +							 no_mtime);
> >  			if (info->status == 0)
> >  				info->bytes_deduped += len;
> >  		}
> > @@ -3219,13 +3229,17 @@ static int clone_finish_inode_update(struct btrfs_trans_handle *trans,
> >  				     struct inode *inode,
> >  				     u64 endoff,
> >  				     const u64 destoff,
> > -				     const u64 olen)
> > +				     const u64 olen,
> > +				     int no_mtime)
> >  {
> >  	struct btrfs_root *root = BTRFS_I(inode)->root;
> >  	int ret;
> >  
> >  	inode_inc_iversion(inode);
> > -	inode->i_mtime = inode->i_ctime = CURRENT_TIME;
> > +	if (no_mtime)
> > +		inode->i_ctime = CURRENT_TIME;
> > +	else
> > +		inode->i_mtime = inode->i_ctime = CURRENT_TIME;
> >  	/*
> >  	 * We round up to the block size at eof when determining which
> >  	 * extents to clone above, but shouldn't round up the file size.
> > @@ -3316,7 +3330,7 @@ static void clone_update_extent_map(struct inode *inode,
> >   */
> >  static int btrfs_clone(struct inode *src, struct inode *inode,
> >  		       const u64 off, const u64 olen, const u64 olen_aligned,
> > -		       const u64 destoff)
> > +		       const u64 destoff, int no_mtime)
> >  {
> >  	struct btrfs_root *root = BTRFS_I(inode)->root;
> >  	struct btrfs_path *path = NULL;
> > @@ -3640,7 +3654,7 @@ process_slot:
> >  					      root->sectorsize);
> >  			ret = clone_finish_inode_update(trans, inode,
> >  							last_dest_end,
> > -							destoff, olen);
> > +							destoff, olen, no_mtime);
> >  			if (ret)
> >  				goto out;
> >  			if (new_key.offset + datal >= destoff + len)
> > @@ -3678,7 +3692,7 @@ process_slot:
> >  		clone_update_extent_map(inode, trans, NULL, last_dest_end,
> >  					destoff + len - last_dest_end);
> >  		ret = clone_finish_inode_update(trans, inode, destoff + len,
> > -						destoff, olen);
> > +						destoff, olen, no_mtime);
> >  	}
> >  
> >  out:
> > @@ -3808,7 +3822,7 @@ static noinline long btrfs_ioctl_clone(struct file *file, unsigned long srcfd,
> >  		btrfs_double_extent_lock(src, off, inode, destoff, len);
> >  	}
> >  
> > -	ret = btrfs_clone(src, inode, off, olen, len, destoff);
> > +	ret = btrfs_clone(src, inode, off, olen, len, destoff, 0);
> >  
> >  	if (same_inode) {
> >  		u64 lock_start = min_t(u64, off, destoff);
> > diff --git a/include/uapi/linux/btrfs.h b/include/uapi/linux/btrfs.h
> > index b6dec05..beeb51c 100644
> > --- a/include/uapi/linux/btrfs.h
> > +++ b/include/uapi/linux/btrfs.h
> 
> > +#define	BTRFS_SAME_NO_MTIME	0x1
> > +#define	BTRFS_SAME_FLAGS	(BTRFS_SAME_NO_MTIME)
> 
> The naming scheme used eg. for the send flags:
> 
> BTRFS_SEND_FLAG_MASK
> BTRFS_SEND_FLAG_NO_FILE_DATA
> 
> So I suggest to follow it:
> 
> BTRFS_SAME_FLAG_MASK
> BTRFS_SAME_FLAG_NO_MTIME
> 
> Though I'd rather see it named it with BTRFS_EXTENT_SAME_ prefix so it
> (almost ...) matches the ioctl name (and is greppable).

Is there any sane use case where we would _want_ EXTENT_SAME to change
the mtime?  We do a lot of work to make sure that none of the files
involved have any sort of content change.  Why do we need the flag at all?

> This is going to be in a public interface so the naming is important.
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