xfs: decide if inode needs inactivation

Add a predicate function to decide if an inode needs (deferred)
inactivation.  Any file that has been unlinked or has speculative
preallocations either for post-EOF writes or for CoW qualifies.
This function will also be used by the upcoming deferred inactivation
patch.

Signed-off-by: Darrick J. Wong <[email protected]>
(cherry picked from commit 	f20a128f44b5eff13afa9f87d76e6310d3607d92)
cherry-pick-repo=kernel/git/djwong/xfs-linux.git

Orabug: 30944736

Signed-off-by: Junxiao Bi <[email protected]>
Reviewed-by: Darrick J. Wong <[email protected]>
Signed-off-by: Brian Maly <[email protected]>

Author: biger410

fs/xfs/xfs_inode.c

@@ -1789,6 +1789,60 @@ xfs_inactive_ifree(
 	return 0;
 }
 
+/*
+ * Returns true if we need to update the on-disk metadata before we can free
+ * the memory used by this inode.  Updates include freeing post-eof
+ * preallocations; and marking the inode free in the inobt if it is
+ * on the unlinked list.
+ */
+bool
+xfs_inode_needs_inactivation(
+	struct xfs_inode	*ip)
+{
+	struct xfs_mount	*mp = ip->i_mount;
+
+	/*
+	 * If the inode is already free, then there can be nothing
+	 * to clean up here.
+	 */
+	if (VFS_I(ip)->i_mode == 0)
+		return false;
+
+	/* If this is a read-only mount, don't do this (would generate I/O) */
+	if (mp->m_flags & XFS_MOUNT_RDONLY)
+		return false;
+
+	if (VFS_I(ip)->i_nlink != 0) {
+		int	error;
+		bool	has;
+
+		/*
+		 * force is true because we are evicting an inode from the
+		 * cache. Post-eof blocks must be freed, lest we end up with
+		 * broken free space accounting.
+		 *
+		 * Note: don't bother with iolock here since lockdep complains
+		 * about acquiring it in reclaim context. We have the only
+		 * reference to the inode at this point anyways.
+		 *
+		 * If the predicate errors out, send the inode through
+		 * inactivation anyway, because that's what we did before.
+		 * The inactivation worker will ignore an inode that doesn't
+		 * actually need it.
+		 */
+		if (!xfs_can_free_eofblocks(ip, true))
+			return false;
+		error = xfs_has_eofblocks(ip, &has);
+		return error != 0 || has;
+	}
+
+	/*
+	 * Link count dropped to zero, which means we have to mark the inode
+	 * free on disk and remove it from the AGI unlinked list.
+	 */
+	return true;
+}
+
 /*
  * xfs_inactive
  *

fs/xfs/xfs_inode.h

@@ -405,6 +405,7 @@ int	xfs_zero_eof(struct xfs_inode *ip, xfs_off_t offset,
 		     xfs_fsize_t isize, bool *did_zeroing);
 int	xfs_iozero(struct xfs_inode *ip, loff_t pos, size_t count);
 int xfs_has_eofblocks(struct xfs_inode *ip, bool *has);
+bool xfs_inode_needs_inactivation(struct xfs_inode *ip);
 
 
 /* from xfs_iops.c */