Commit d0641780 authored by Dave Chinner's avatar Dave Chinner Committed by Darrick J. Wong
Browse files

xfs: simplify xfs_file_iomap_begin() logic 



The current logic that determines whether allocation should be done
has grown somewhat spaghetti like with the addition of IOMAP_NOWAIT
functionality. Separate out each of the different cases into single,
obvious checks to get rid most of the nested IOMAP_NOWAIT checks
in the allocation logic.

Signed-Off-By: default avatarDave Chinner <dchinner@redhat.com>
Reviewed-by: default avatarCarlos Maiolino <cmaiolino@redhat.com>
Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
Reviewed-by: default avatarDarrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: default avatarDarrick J. Wong <darrick.wong@oracle.com>
parent 3460cac1

fs/xfs/xfs_iomap.c

+46 −36
Original line number Diff line number Diff line
@@ -1040,6 +1040,10 @@ xfs_file_iomap_begin( 
			goto out_unlock;

	}



	/* Non-modifying mapping requested, so we are done */

	if (!(flags & (IOMAP_WRITE | IOMAP_ZERO)))

		goto out_found;



	if (xfs_is_reflink_inode(ip) &&

	    ((flags & IOMAP_WRITE) ||

	     ((flags & IOMAP_ZERO) && needs_cow_for_zeroing(&imap, nimaps)))) {
@@ -1068,29 +1072,33 @@ xfs_file_iomap_begin( 
		length = XFS_FSB_TO_B(mp, end_fsb) - offset;

	}



	if ((flags & IOMAP_WRITE) && imap_needs_alloc(inode, &imap, nimaps)) {

		/*

		 * If nowait is set bail since we are going to make

		 * allocations.

		 */

	/* Don't need to allocate over holes when doing zeroing operations. */

	if (flags & IOMAP_ZERO)

		goto out_found;



	if (!imap_needs_alloc(inode, &imap, nimaps))

		goto out_found;



	/* If nowait is set bail since we are going to make allocations. */

	if (flags & IOMAP_NOWAIT) {

		error = -EAGAIN;

		goto out_unlock;

	}



	/*

		 * We cap the maximum length we map here to MAX_WRITEBACK_PAGES

		 * pages to keep the chunks of work done where somewhat symmetric

		 * with the work writeback does. This is a completely arbitrary

		 * number pulled out of thin air as a best guess for initial

		 * testing.

	 * We cap the maximum length we map to a sane size  to keep the chunks

	 * of work done where somewhat symmetric with the work writeback does.

	 * This is a completely arbitrary number pulled out of thin air as a

	 * best guess for initial testing.

	 *

		 * Note that the values needs to be less than 32-bits wide until

		 * the lower level functions are updated.

	 * Note that the values needs to be less than 32-bits wide until the

	 * lower level functions are updated.

	 */

	length = min_t(loff_t, length, 1024 * PAGE_SIZE);



	/*

		 * xfs_iomap_write_direct() expects the shared lock. It

		 * is unlocked on return.

	 * xfs_iomap_write_direct() expects the shared lock. It is unlocked on

	 * return.

	 */

	if (lockmode == XFS_ILOCK_EXCL)

		xfs_ilock_demote(ip, lockmode);
@@ -1101,13 +1109,8 @@ xfs_file_iomap_begin( 


	iomap->flags = IOMAP_F_NEW;

	trace_xfs_iomap_alloc(ip, offset, length, 0, &imap);

	} else {

		ASSERT(nimaps);



		xfs_iunlock(ip, lockmode);

		trace_xfs_iomap_found(ip, offset, length, 0, &imap);

	}



out_finish:

	if (xfs_ipincount(ip) && (ip->i_itemp->ili_fsync_fields

				& ~XFS_ILOG_TIMESTAMP))

		iomap->flags |= IOMAP_F_DIRTY;
@@ -1117,6 +1120,13 @@ xfs_file_iomap_begin( 
	if (shared)

		iomap->flags |= IOMAP_F_SHARED;

	return 0;



out_found:

	ASSERT(nimaps);

	xfs_iunlock(ip, lockmode);

	trace_xfs_iomap_found(ip, offset, length, 0, &imap);

	goto out_finish;



out_unlock:

	xfs_iunlock(ip, lockmode);

	return error;

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