Check suspendability on the mountpoint returned by VOP_GETWRITEMOUNT.

This obviates the need for a MNTK_SUSPENDABLE flag, since passthrough
filesystems like nullfs and unionfs no longer need to inherit this
information from their lower layer(s). This change also restores the
pre-r273336 behaviour of using the presence of a susp_clean VFS method to
request suspension support.

Reviewed by:	kib, mjg
Differential Revision:	https://reviews.freebsd.org/D2937

sys/fs/nullfs/null_vfsops.c

@@ -199,7 +199,7 @@ nullfs_mount(struct mount *mp)
 	}
 	mp->mnt_kern_flag |= MNTK_LOOKUP_EXCL_DOTDOT;
 	mp->mnt_kern_flag |= lowerrootvp->v_mount->mnt_kern_flag &
-	    (MNTK_SUSPENDABLE | MNTK_USES_BCACHE);
+	    MNTK_USES_BCACHE;
 	MNT_IUNLOCK(mp);
 	mp->mnt_data = xmp;
 	vfs_getnewfsid(mp);

sys/fs/tmpfs/tmpfs_vfsops.c

@@ -75,6 +75,7 @@ static int	tmpfs_root(struct mount *, int flags, struct vnode **);
 static int	tmpfs_fhtovp(struct mount *, struct fid *, int,
 		    struct vnode **);
 static int	tmpfs_statfs(struct mount *, struct statfs *);
+static void	tmpfs_susp_clean(struct mount *);
 
 static const char *tmpfs_opts[] = {
 	"from", "size", "maxfilesize", "inodes", "uid", "gid", "mode", "export",
@@ -256,7 +257,7 @@ tmpfs_mount(struct mount *mp)
 
 	MNT_ILOCK(mp);
 	mp->mnt_flag |= MNT_LOCAL;
-	mp->mnt_kern_flag |= MNTK_LOOKUP_SHARED | MNTK_SUSPENDABLE;
+	mp->mnt_kern_flag |= MNTK_LOOKUP_SHARED;
 	MNT_IUNLOCK(mp);
 
 	mp->mnt_data = tmp;
@@ -462,6 +463,14 @@ tmpfs_sync(struct mount *mp, int waitfor)
 	return (0);
 }
 
+/*
+ * The presence of a susp_clean method tells the VFS to track writes.
+ */
+static void
+tmpfs_susp_clean(struct mount *mp __unused)
+{
+}
+
 /*
  * tmpfs vfs operations.
  */
@@ -473,5 +482,6 @@ struct vfsops tmpfs_vfsops = {
 	.vfs_statfs =			tmpfs_statfs,
 	.vfs_fhtovp =			tmpfs_fhtovp,
 	.vfs_sync =			tmpfs_sync,
+	.vfs_susp_clean =		tmpfs_susp_clean,
 };
 VFS_SET(tmpfs_vfsops, tmpfs, VFCF_JAIL);

sys/fs/unionfs/union_vfsops.c

@@ -294,9 +294,6 @@ unionfs_domount(struct mount *mp)
 	if ((ump->um_lowervp->v_mount->mnt_flag & MNT_LOCAL) &&
 	    (ump->um_uppervp->v_mount->mnt_flag & MNT_LOCAL))
 		mp->mnt_flag |= MNT_LOCAL;
-
-	if ((ump->um_uppervp->v_mount->mnt_kern_flag & MNTK_SUSPENDABLE) != 0)
-		mp->mnt_kern_flag |= MNTK_SUSPENDABLE;
 	MNT_IUNLOCK(mp);
 
 	/*

sys/kern/vfs_vnops.c

@@ -1589,22 +1589,10 @@ vn_closefile(fp, td)
 }
 
 static bool
-vn_suspendable_mp(struct mount *mp)
+vn_suspendable(struct mount *mp)
 {
 
-	return ((mp->mnt_kern_flag & MNTK_SUSPENDABLE) != 0);
+	return (mp->mnt_op->vfs_susp_clean != NULL);
-}
-
-static bool
-vn_suspendable(struct vnode *vp, struct mount **mpp)
-{
-
-	if (vp != NULL)
-		*mpp = vp->v_mount;
-	if (*mpp == NULL)
-		return (false);
-
-	return (vn_suspendable_mp(*mpp));
 }
 
 /*
@@ -1657,11 +1645,6 @@ vn_start_write(struct vnode *vp, struct mount **mpp, int flags)
 
 	KASSERT((flags & V_MNTREF) == 0 || (*mpp != NULL && vp == NULL),
 	    ("V_MNTREF requires mp"));
-	if (!vn_suspendable(vp, mpp)) {
-		if ((flags & V_MNTREF) != 0)
-			vfs_rel(*mpp);
-		return (0);
-	}
 
 	error = 0;
 	/*
@@ -1679,6 +1662,12 @@ vn_start_write(struct vnode *vp, struct mount **mpp, int flags)
 	if ((mp = *mpp) == NULL)
 		return (0);
 
+	if (!vn_suspendable(mp)) {
+		if (vp != NULL || (flags & V_MNTREF) != 0)
+			vfs_rel(mp);
+		return (0);
+	}
+
 	/*
 	 * VOP_GETWRITEMOUNT() returns with the mp refcount held through
 	 * a vfs_ref().
@@ -1708,11 +1697,6 @@ vn_start_secondary_write(struct vnode *vp, struct mount **mpp, int flags)
 
 	KASSERT((flags & V_MNTREF) == 0 || (*mpp != NULL && vp == NULL),
 	    ("V_MNTREF requires mp"));
-	if (!vn_suspendable(vp, mpp)) {
-		if ((flags & V_MNTREF) != 0)
-			vfs_rel(*mpp);
-		return (0);
-	}
 
  retry:
 	if (vp != NULL) {
@@ -1730,6 +1714,12 @@ vn_start_secondary_write(struct vnode *vp, struct mount **mpp, int flags)
 	if ((mp = *mpp) == NULL)
 		return (0);
 
+	if (!vn_suspendable(mp)) {
+		if (vp != NULL || (flags & V_MNTREF) != 0)
+			vfs_rel(mp);
+		return (0);
+	}
+
 	/*
 	 * VOP_GETWRITEMOUNT() returns with the mp refcount held through
 	 * a vfs_ref().
@@ -1772,7 +1762,7 @@ void
 vn_finished_write(mp)
 	struct mount *mp;
 {
-	if (mp == NULL || !vn_suspendable_mp(mp))
+	if (mp == NULL || !vn_suspendable(mp))
 		return;
 	MNT_ILOCK(mp);
 	MNT_REL(mp);
@@ -1795,7 +1785,7 @@ void
 vn_finished_secondary_write(mp)
 	struct mount *mp;
 {
-	if (mp == NULL || !vn_suspendable_mp(mp))
+	if (mp == NULL || !vn_suspendable(mp))
 		return;
 	MNT_ILOCK(mp);
 	MNT_REL(mp);
@@ -1818,7 +1808,7 @@ vfs_write_suspend(struct mount *mp, int flags)
 {
 	int error;
 
-	MPASS(vn_suspendable_mp(mp));
+	MPASS(vn_suspendable(mp));
 
 	MNT_ILOCK(mp);
 	if (mp->mnt_susp_owner == curthread) {
@@ -1861,7 +1851,7 @@ void
 vfs_write_resume(struct mount *mp, int flags)
 {
 
-	MPASS(vn_suspendable_mp(mp));
+	MPASS(vn_suspendable(mp));
 
 	MNT_ILOCK(mp);
 	if ((mp->mnt_kern_flag & MNTK_SUSPEND) != 0) {
@@ -1896,7 +1886,7 @@ vfs_write_suspend_umnt(struct mount *mp)
 {
 	int error;
 
-	MPASS(vn_suspendable_mp(mp));
+	MPASS(vn_suspendable(mp));
 	KASSERT((curthread->td_pflags & TDP_IGNSUSP) == 0,
 	    ("vfs_write_suspend_umnt: recursed"));
 

sys/sys/mount.h

@@ -362,7 +362,7 @@ void          __mnt_vnode_markerfree_active(struct vnode **mvp, struct mount *);
 #define	MNTK_SUSPEND	0x08000000	/* request write suspension */
 #define	MNTK_SUSPEND2	0x04000000	/* block secondary writes */
 #define	MNTK_SUSPENDED	0x10000000	/* write operations are suspended */
-#define	MNTK_SUSPENDABLE	0x20000000 /* writes can be suspended */
+#define	MNTK_UNUSED1	0x20000000
 #define MNTK_LOOKUP_SHARED	0x40000000 /* FS supports shared lock lookups */
 #define	MNTK_NOKNOTE	0x80000000	/* Don't send KNOTEs from VOP hooks */
 

sys/ufs/ffs/ffs_vfsops.c

@@ -1055,8 +1055,7 @@ ffs_mountfs(devvp, mp, td)
 	 */
 	MNT_ILOCK(mp);
 	mp->mnt_kern_flag |= MNTK_LOOKUP_SHARED | MNTK_EXTENDED_SHARED |
-	    MNTK_NO_IOPF | MNTK_UNMAPPED_BUFS | MNTK_SUSPENDABLE |
+	    MNTK_NO_IOPF | MNTK_UNMAPPED_BUFS | MNTK_USES_BCACHE;
-	    MNTK_USES_BCACHE;
 	MNT_IUNLOCK(mp);
 #ifdef UFS_EXTATTR
 #ifdef UFS_EXTATTR_AUTOSTART