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, 9 insertions, 0 deletions

diff --git a/sys/kern/sys_socket.c b/sys/kern/sys_socket.c
index 7e4547c..8e6b5f2 100644
--- a/sys/kern/sys_socket.c
+++ b/sys/kern/sys_socket.c
@@ -59,6 +59,7 @@ __FBSDID("$FreeBSD$");
 struct fileops	socketops = {
 	.fo_read = soo_read,
 	.fo_write = soo_write,
+	.fo_truncate = soo_truncate,
 	.fo_ioctl = soo_ioctl,
 	.fo_poll = soo_poll,
 	.fo_kqfilter = soo_kqfilter,
@@ -110,6 +111,14 @@ soo_write(struct file *fp, struct uio *uio, struct ucred *active_cred,
 }
 
 int
+soo_truncate(struct file *fp, off_t length, struct ucred *active_cred,
+    struct thread *td)
+{
+
+	return (EINVAL);
+}
+
+int
 soo_ioctl(struct file *fp, u_long cmd, void *data, struct ucred *active_cred,
     struct thread *td)
 {