Provide vfs suspension support only for filesystems which need it.

Need is expressed by providing vfs_susp_clean function in vfsops.

Differential Revision:	D952
Reviewed by:	kib (previous version)
MFC after:	2 weeks

3 files changed, 45 insertions, 7 deletions

diff --git a/sys/fs/tmpfs/tmpfs_vfsops.c b/sys/fs/tmpfs/tmpfs_vfsops.c
index cb4a32b..f0bb96b 100644
--- a/sys/fs/tmpfs/tmpfs_vfsops.c
+++ b/sys/fs/tmpfs/tmpfs_vfsops.c
@@ -427,6 +427,14 @@ tmpfs_sync(struct mount *mp, int waitfor)
 }
 
 /*
+ * A stub created so that vfs does vn_start_write for this filesystem
+ */
+static void
+tmpfs_susp_clean(struct mount *mp)
+{
+}
+
+/*
  * tmpfs vfs operations.
  */
 
@@ -437,5 +445,6 @@ 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);
diff --git a/sys/kern/vfs_vnops.c b/sys/kern/vfs_vnops.c
index b86ffa7..7a72137 100644
--- a/sys/kern/vfs_vnops.c
+++ b/sys/kern/vfs_vnops.c
@@ -1572,6 +1572,25 @@ vn_closefile(fp, td)
 	return (error);
 }
 
+static bool
+vn_suspendable_mp(struct mount *mp)
+{
+
+	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));
+}
+
 /*
  * Preparing to start a filesystem write operation. If the operation is
  * permitted, then we bump the count of operations in progress and
@@ -1621,6 +1640,9 @@ vn_start_write(vp, mpp, flags)
 	struct mount *mp;
 	int error;
 
+	if (!vn_suspendable(vp, mpp))
+		return (0);
+
 	error = 0;
 	/*
 	 * If a vnode is provided, get and return the mount point that
@@ -1667,6 +1689,9 @@ vn_start_secondary_write(vp, mpp, flags)
 	struct mount *mp;
 	int error;
 
+	if (!vn_suspendable(vp, mpp))
+		return (0);
+
  retry:
 	if (vp != NULL) {
 		if ((error = VOP_GETWRITEMOUNT(vp, mpp)) != 0) {
@@ -1724,7 +1749,7 @@ void
 vn_finished_write(mp)
 	struct mount *mp;
 {
-	if (mp == NULL)
+	if (mp == NULL || !vn_suspendable_mp(mp))
 		return;
 	MNT_ILOCK(mp);
 	MNT_REL(mp);
@@ -1747,7 +1772,7 @@ void
 vn_finished_secondary_write(mp)
 	struct mount *mp;
 {
-	if (mp == NULL)
+	if (mp == NULL || !vn_suspendable_mp(mp))
 		return;
 	MNT_ILOCK(mp);
 	MNT_REL(mp);
@@ -1770,6 +1795,8 @@ vfs_write_suspend(struct mount *mp, int flags)
 {
 	int error;
 
+	MPASS(vn_suspendable_mp(mp));
+
 	MNT_ILOCK(mp);
 	if (mp->mnt_susp_owner == curthread) {
 		MNT_IUNLOCK(mp);
@@ -1811,6 +1838,8 @@ void
 vfs_write_resume(struct mount *mp, int flags)
 {
 
+	MPASS(vn_suspendable_mp(mp));
+
 	MNT_ILOCK(mp);
 	if ((mp->mnt_kern_flag & MNTK_SUSPEND) != 0) {
 		KASSERT(mp->mnt_susp_owner == curthread, ("mnt_susp_owner"));
@@ -1844,6 +1873,7 @@ vfs_write_suspend_umnt(struct mount *mp)
 {
 	int error;
 
+	MPASS(vn_suspendable_mp(mp));
 	KASSERT((curthread->td_pflags & TDP_IGNSUSP) == 0,
 	    ("vfs_write_suspend_umnt: recursed"));
 
diff --git a/sys/sys/mount.h b/sys/sys/mount.h
index d186599..633c6db 100644
--- a/sys/sys/mount.h
+++ b/sys/sys/mount.h
@@ -754,11 +754,10 @@ vfs_statfs_t	__vfs_statfs;
 	_rc; })
 
 #define	VFS_SUSP_CLEAN(MP) do {						\
-	if (*(MP)->mnt_op->vfs_susp_clean != NULL) {			\
-		VFS_PROLOGUE(MP);					\
-		(*(MP)->mnt_op->vfs_susp_clean)(MP);			\
-		VFS_EPILOGUE(MP);					\
-	}								\
+	MPASS(*(MP)->mnt_op->vfs_susp_clean != NULL); 			\
+	VFS_PROLOGUE(MP);						\
+	(*(MP)->mnt_op->vfs_susp_clean)(MP);				\
+	VFS_EPILOGUE(MP);						\
 } while (0)
 
 #define	VFS_RECLAIM_LOWERVP(MP, VP) do {				\