Re: [PATCH 04/12] xfs: initialize ioma->flags in xfs_bmbt_to_iomap

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Mon, Jun 24, 2019 at 07:52:45AM +0200, Christoph Hellwig wrote:
> Currently we don't overwrite the flags field in the iomap in
> xfs_bmbt_to_iomap.  This works fine with 0-initialized iomaps on stack,
> but is harmful once we want to be able to reuse an iomap in the
> writeback code.

Is that going to affect all the other iomap users, or is xfs the only
one that assumes zero-initialized iomaps being passed into
->iomap_begin?

--D

> Replace the shared paramter with a set of initial
> flags an thus ensures the flags field is always reinitialized.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  fs/xfs/xfs_iomap.c | 28 +++++++++++++++++-----------
>  fs/xfs/xfs_iomap.h |  2 +-
>  fs/xfs/xfs_pnfs.c  |  2 +-
>  3 files changed, 19 insertions(+), 13 deletions(-)
> 
> diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
> index 63d323916bba..6b29452bfba0 100644
> --- a/fs/xfs/xfs_iomap.c
> +++ b/fs/xfs/xfs_iomap.c
> @@ -57,7 +57,7 @@ xfs_bmbt_to_iomap(
>  	struct xfs_inode	*ip,
>  	struct iomap		*iomap,
>  	struct xfs_bmbt_irec	*imap,
> -	bool			shared)
> +	u16			flags)
>  {
>  	struct xfs_mount	*mp = ip->i_mount;
>  
> @@ -82,12 +82,11 @@ xfs_bmbt_to_iomap(
>  	iomap->length = XFS_FSB_TO_B(mp, imap->br_blockcount);
>  	iomap->bdev = xfs_find_bdev_for_inode(VFS_I(ip));
>  	iomap->dax_dev = xfs_find_daxdev_for_inode(VFS_I(ip));
> +	iomap->flags = flags;
>  
>  	if (xfs_ipincount(ip) &&
>  	    (ip->i_itemp->ili_fsync_fields & ~XFS_ILOG_TIMESTAMP))
>  		iomap->flags |= IOMAP_F_DIRTY;
> -	if (shared)
> -		iomap->flags |= IOMAP_F_SHARED;
>  	return 0;
>  }
>  
> @@ -543,6 +542,7 @@ xfs_file_iomap_begin_delay(
>  	struct xfs_iext_cursor	icur, ccur;
>  	xfs_fsblock_t		prealloc_blocks = 0;
>  	bool			eof = false, cow_eof = false, shared = false;
> +	u16			iomap_flags = 0;
>  	int			whichfork = XFS_DATA_FORK;
>  	int			error = 0;
>  
> @@ -710,7 +710,7 @@ xfs_file_iomap_begin_delay(
>  	 * Flag newly allocated delalloc blocks with IOMAP_F_NEW so we punch
>  	 * them out if the write happens to fail.
>  	 */
> -	iomap->flags |= IOMAP_F_NEW;
> +	iomap_flags |= IOMAP_F_NEW;
>  	trace_xfs_iomap_alloc(ip, offset, count, whichfork,
>  			whichfork == XFS_DATA_FORK ? &imap : &cmap);
>  done:
> @@ -718,14 +718,17 @@ xfs_file_iomap_begin_delay(
>  		if (imap.br_startoff > offset_fsb) {
>  			xfs_trim_extent(&cmap, offset_fsb,
>  					imap.br_startoff - offset_fsb);
> -			error = xfs_bmbt_to_iomap(ip, iomap, &cmap, true);
> +			error = xfs_bmbt_to_iomap(ip, iomap, &cmap,
> +					IOMAP_F_SHARED);
>  			goto out_unlock;
>  		}
>  		/* ensure we only report blocks we have a reservation for */
>  		xfs_trim_extent(&imap, cmap.br_startoff, cmap.br_blockcount);
>  		shared = true;
>  	}
> -	error = xfs_bmbt_to_iomap(ip, iomap, &imap, shared);
> +	if (shared)
> +		iomap_flags |= IOMAP_F_SHARED;
> +	error = xfs_bmbt_to_iomap(ip, iomap, &imap, iomap_flags);
>  out_unlock:
>  	xfs_iunlock(ip, XFS_ILOCK_EXCL);
>  	return error;
> @@ -933,6 +936,7 @@ xfs_file_iomap_begin(
>  	xfs_fileoff_t		offset_fsb, end_fsb;
>  	int			nimaps = 1, error = 0;
>  	bool			shared = false;
> +	u16			iomap_flags = 0;
>  	unsigned		lockmode;
>  
>  	if (XFS_FORCED_SHUTDOWN(mp))
> @@ -1048,11 +1052,13 @@ xfs_file_iomap_begin(
>  	if (error)
>  		return error;
>  
> -	iomap->flags |= IOMAP_F_NEW;
> +	iomap_flags |= IOMAP_F_NEW;
>  	trace_xfs_iomap_alloc(ip, offset, length, XFS_DATA_FORK, &imap);
>  
>  out_finish:
> -	return xfs_bmbt_to_iomap(ip, iomap, &imap, shared);
> +	if (shared)
> +		iomap_flags |= IOMAP_F_SHARED;
> +	return xfs_bmbt_to_iomap(ip, iomap, &imap, iomap_flags);
>  
>  out_found:
>  	ASSERT(nimaps);
> @@ -1196,7 +1202,7 @@ xfs_seek_iomap_begin(
>  		if (data_fsb < cow_fsb + cmap.br_blockcount)
>  			end_fsb = min(end_fsb, data_fsb);
>  		xfs_trim_extent(&cmap, offset_fsb, end_fsb);
> -		error = xfs_bmbt_to_iomap(ip, iomap, &cmap, true);
> +		error = xfs_bmbt_to_iomap(ip, iomap, &cmap, IOMAP_F_SHARED);
>  		/*
>  		 * This is a COW extent, so we must probe the page cache
>  		 * because there could be dirty page cache being backed
> @@ -1218,7 +1224,7 @@ xfs_seek_iomap_begin(
>  	imap.br_state = XFS_EXT_NORM;
>  done:
>  	xfs_trim_extent(&imap, offset_fsb, end_fsb);
> -	error = xfs_bmbt_to_iomap(ip, iomap, &imap, false);
> +	error = xfs_bmbt_to_iomap(ip, iomap, &imap, 0);
>  out_unlock:
>  	xfs_iunlock(ip, lockmode);
>  	return error;
> @@ -1264,7 +1270,7 @@ xfs_xattr_iomap_begin(
>  	if (error)
>  		return error;
>  	ASSERT(nimaps);
> -	return xfs_bmbt_to_iomap(ip, iomap, &imap, false);
> +	return xfs_bmbt_to_iomap(ip, iomap, &imap, 0);
>  }
>  
>  const struct iomap_ops xfs_xattr_iomap_ops = {
> diff --git a/fs/xfs/xfs_iomap.h b/fs/xfs/xfs_iomap.h
> index 5c2f6aa6d78f..71d0ae460c44 100644
> --- a/fs/xfs/xfs_iomap.h
> +++ b/fs/xfs/xfs_iomap.h
> @@ -16,7 +16,7 @@ int xfs_iomap_write_direct(struct xfs_inode *, xfs_off_t, size_t,
>  int xfs_iomap_write_unwritten(struct xfs_inode *, xfs_off_t, xfs_off_t, bool);
>  
>  int xfs_bmbt_to_iomap(struct xfs_inode *, struct iomap *,
> -		struct xfs_bmbt_irec *, bool shared);
> +		struct xfs_bmbt_irec *, u16);
>  xfs_extlen_t xfs_eof_alignment(struct xfs_inode *ip, xfs_extlen_t extsize);
>  
>  static inline xfs_filblks_t
> diff --git a/fs/xfs/xfs_pnfs.c b/fs/xfs/xfs_pnfs.c
> index bde2c9f56a46..12f664785248 100644
> --- a/fs/xfs/xfs_pnfs.c
> +++ b/fs/xfs/xfs_pnfs.c
> @@ -185,7 +185,7 @@ xfs_fs_map_blocks(
>  	}
>  	xfs_iunlock(ip, XFS_IOLOCK_EXCL);
>  
> -	error = xfs_bmbt_to_iomap(ip, iomap, &imap, false);
> +	error = xfs_bmbt_to_iomap(ip, iomap, &imap, 0);
>  	*device_generation = mp->m_generation;
>  	return error;
>  out_unlock:
> -- 
> 2.20.1
>