Make ftruncate a 'struct file' operation rather than a vnode operation.

This makes it possible to support ftruncate() on non-vnode file types in
the future.
- 'struct fileops' grows a 'fo_truncate' method to handle an ftruncate() on
  a given file descriptor.
- ftruncate() moves to kern/sys_generic.c and now just fetches a file
  object and invokes fo_truncate().
- The vnode-specific portions of ftruncate() move to vn_truncate() in
  vfs_vnops.c which implements fo_truncate() for vnode file types.
- Non-vnode file types return EINVAL in their fo_truncate() method.

Submitted by:	rwatson

1 files changed, 8 insertions, 0 deletions

diff --git a/sys/kern/kern_descrip.c b/sys/kern/kern_descrip.c
index d68854e..24438dd 100644
--- a/sys/kern/kern_descrip.c
+++ b/sys/kern/kern_descrip.c
@@ -2760,6 +2760,13 @@ badfo_readwrite(struct file *fp, struct uio *uio, struct ucred *active_cred, int
 }
 
 static int
+badfo_truncate(struct file *fp, off_t length, struct ucred *active_cred, struct thread *td)
+{
+
+	return (EINVAL);
+}
+
+static int
 badfo_ioctl(struct file *fp, u_long com, void *data, struct ucred *active_cred, struct thread *td)
 {
 
@@ -2797,6 +2804,7 @@ badfo_close(struct file *fp, struct thread *td)
 struct fileops badfileops = {
 	.fo_read = badfo_readwrite,
 	.fo_write = badfo_readwrite,
+	.fo_truncate = badfo_truncate,
 	.fo_ioctl = badfo_ioctl,
 	.fo_poll = badfo_poll,
 	.fo_kqfilter = badfo_kqfilter,