Re: [PATCH 05/10] xfs: split XFS_BMAPI_DELALLOC handling from xfs_bmapi_write

[Brian Foster <bfoster@redhat.com>]

On Mon, Feb 11, 2019 at 01:54:22PM +0100, Christoph Hellwig wrote:
> Delalloc conversion has traditionally been part of our function to
> allocate blocks on disk (first xfs_bmapi, then xfs_bmapi_write), but
> delalloc conversion is a little special as we really do not want
> to allocate blocks over holes, for which we don't have reservations.
> 
> Split the delalloc conversions into a separate helper to keep the
> code simple and structured.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---

Reviewed-by: Brian Foster <bfoster@redhat.com>

>  fs/xfs/libxfs/xfs_bmap.c | 104 +++++++++++++++++++++------------------
>  fs/xfs/libxfs/xfs_bmap.h |   4 --
>  2 files changed, 56 insertions(+), 52 deletions(-)
> 
> diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c
> index a9c9bd39d822..be2cb5800e02 100644
> --- a/fs/xfs/libxfs/xfs_bmap.c
> +++ b/fs/xfs/libxfs/xfs_bmap.c
> @@ -4327,22 +4327,6 @@ xfs_bmapi_write(
>  	bma.datatype = 0;
>  	bma.minleft = xfs_bmapi_minleft(tp, ip, whichfork);
>  
> -	/*
> -	 * The delalloc flag means the caller wants to allocate the entire
> -	 * delalloc extent backing bno where bno may not necessarily match the
> -	 * startoff. Now that we've looked up the extent, reset the range to
> -	 * map based on the extent in the file. If we're in a hole, this may be
> -	 * an error so don't adjust anything.
> -	 */
> -	if ((flags & XFS_BMAPI_DELALLOC) &&
> -	    !eof && bno >= bma.got.br_startoff) {
> -		bno = bma.got.br_startoff;
> -		len = bma.got.br_blockcount;
> -#ifdef DEBUG
> -		orig_bno = bno;
> -		orig_len = len;
> -#endif
> -	}
>  	n = 0;
>  	end = bno + len;
>  	obno = bno;
> @@ -4359,26 +4343,7 @@ xfs_bmapi_write(
>  			ASSERT(!((flags & XFS_BMAPI_CONVERT) &&
>  			         (flags & XFS_BMAPI_COWFORK)));
>  
> -			if (flags & XFS_BMAPI_DELALLOC) {
> -				/*
> -				 * For the COW fork we can reasonably get a
> -				 * request for converting an extent that races
> -				 * with other threads already having converted
> -				 * part of it, as there converting COW to
> -				 * regular blocks is not protected using the
> -				 * IOLOCK.
> -				 */
> -				ASSERT(flags & XFS_BMAPI_COWFORK);
> -				if (!(flags & XFS_BMAPI_COWFORK)) {
> -					error = -EIO;
> -					goto error0;
> -				}
> -
> -				if (eof || bno >= end)
> -					break;
> -			} else {
> -				need_alloc = true;
> -			}
> +			need_alloc = true;
>  		} else if (isnullstartblock(bma.got.br_startblock)) {
>  			wasdelay = true;
>  		}
> @@ -4487,23 +4452,66 @@ xfs_bmapi_convert_delalloc(
>  	int			whichfork,
>  	struct xfs_bmbt_irec	*imap)
>  {
> -	int			flags = XFS_BMAPI_DELALLOC;
> -	int			nimaps = 1;
> +	struct xfs_ifork	*ifp = XFS_IFORK_PTR(ip, whichfork);
> +	struct xfs_bmalloca	bma = { NULL };
>  	int			error;
> -	int			total = XFS_EXTENTADD_SPACE_RES(ip->i_mount,
> -								XFS_DATA_FORK);
>  
> -	if (whichfork == XFS_COW_FORK)
> -		flags |= XFS_BMAPI_COWFORK | XFS_BMAPI_PREALLOC;
> +	if (!xfs_iext_lookup_extent(ip, ifp, offset_fsb, &bma.icur, &bma.got) ||
> +	    bma.got.br_startoff > offset_fsb) {
> +		/*
> +		 * No extent found in the range we are trying to convert.  This
> +		 * should only happen for the COW fork, where another thread
> +		 * might have moved the extent to the data fork in the meantime.
> +		 */
> +		WARN_ON_ONCE(whichfork != XFS_COW_FORK);
> +		return -EAGAIN;
> +	}
>  
>  	/*
> -	 * The delalloc flag means to allocate the entire extent; pass a dummy
> -	 * length of 1.
> +	 * If we find a real extent here we raced with another thread converting
> +	 * the extent.  Just return the real extent at this offset.
>  	 */
> -	error = xfs_bmapi_write(tp, ip, offset_fsb, 1, flags, total, imap,
> -				&nimaps);
> -	if (!error && !nimaps)
> -		error = -EFSCORRUPTED;
> +	if (!isnullstartblock(bma.got.br_startblock)) {
> +		*imap = bma.got;
> +		return 0;
> +	}
> +
> +	bma.tp = tp;
> +	bma.ip = ip;
> +	bma.wasdel = true;
> +	bma.offset = bma.got.br_startoff;
> +	bma.length = max_t(xfs_filblks_t, bma.got.br_blockcount, MAXEXTLEN);
> +	bma.total = XFS_EXTENTADD_SPACE_RES(ip->i_mount, XFS_DATA_FORK);
> +	bma.minleft = xfs_bmapi_minleft(tp, ip, whichfork);
> +	if (whichfork == XFS_COW_FORK)
> +		bma.flags = XFS_BMAPI_COWFORK | XFS_BMAPI_PREALLOC;
> +
> +	if (!xfs_iext_peek_prev_extent(ifp, &bma.icur, &bma.prev))
> +		bma.prev.br_startoff = NULLFILEOFF;
> +
> +	error = xfs_bmapi_allocate(&bma);
> +	if (error)
> +		goto out_finish;
> +	if (WARN_ON_ONCE(bma.blkno == NULLFSBLOCK)) {
> +		error = -ENOSPC;
> +		goto out_finish;
> +	}
> +
> +	ASSERT(!isnullstartblock(bma.got.br_startblock));
> +	ASSERT(bma.got.br_startblock || XFS_IS_REALTIME_INODE(ip));
> +	*imap = bma.got;
> +
> +	if (whichfork == XFS_COW_FORK) {
> +		error = xfs_refcount_alloc_cow_extent(tp, bma.blkno,
> +				bma.length);
> +		if (error)
> +			goto out_finish;
> +	}
> +
> +	error = xfs_bmap_btree_to_extents(tp, ip, bma.cur, &bma.logflags,
> +			whichfork);
> +out_finish:
> +	xfs_bmapi_finish(&bma, whichfork, error);
>  	return error;
>  }
>  
> diff --git a/fs/xfs/libxfs/xfs_bmap.h b/fs/xfs/libxfs/xfs_bmap.h
> index 4dc7d1a02b35..b5eca7a26949 100644
> --- a/fs/xfs/libxfs/xfs_bmap.h
> +++ b/fs/xfs/libxfs/xfs_bmap.h
> @@ -95,9 +95,6 @@ struct xfs_extent_free_item
>  /* Map something in the CoW fork. */
>  #define XFS_BMAPI_COWFORK	0x200
>  
> -/* Only convert delalloc space, don't allocate entirely new extents */
> -#define XFS_BMAPI_DELALLOC	0x400
> -
>  /* Only convert unwritten extents, don't allocate new blocks */
>  #define XFS_BMAPI_CONVERT_ONLY	0x800
>  
> @@ -117,7 +114,6 @@ struct xfs_extent_free_item
>  	{ XFS_BMAPI_ZERO,	"ZERO" }, \
>  	{ XFS_BMAPI_REMAP,	"REMAP" }, \
>  	{ XFS_BMAPI_COWFORK,	"COWFORK" }, \
> -	{ XFS_BMAPI_DELALLOC,	"DELALLOC" }, \
>  	{ XFS_BMAPI_CONVERT_ONLY, "CONVERT_ONLY" }, \
>  	{ XFS_BMAPI_NODISCARD,	"NODISCARD" }, \
>  	{ XFS_BMAPI_NORMAP,	"NORMAP" }
> -- 
> 2.20.1
>