Migrate the sendfile_sync structure into a public(ish) API in preparation

for extending and reusing it.

The sendfile_sync wrapper is mostly just a "mbuf transaction" wrapper,
used to indicate that the backing store for a group of mbufs has completed.
It's only being used by sendfile for now and it's only implementing a
sleep/wakeup rendezvous.  However, there are other potential signaling
paths (kqueue) and other potential uses (socket zero-copy write) where the
same mechanism would also be useful.

So, with that in mind:

* extract the sendfile_sync code out into sf_sync_*() methods
* teach the sf_sync_alloc method about the current config flag -
  it will eventually know about kqueue.
* move the sendfile_sync code out of do_sendfile() - the only thing
  it now knows about is the sfs pointer.  The guts of the sync
  rendezvous (setup, rendezvous/wait, free) is now done in the
  syscall wrapper.
* .. and teach the 32-bit compat sendfile call the same.

This should be a no-op.  It's primarily preparation work for teaching
the sendfile_sync about kqueue notification.

Tested:

* Peter Holm's sendfile stress / regression scripts

Sponsored by:	Netflix, Inc.

1 files changed, 7 insertions, 3 deletions

diff --git a/sys/sys/file.h b/sys/sys/file.h
index 7b373f0d7091..b7d358b7643c 100644
--- a/sys/sys/file.h
+++ b/sys/sys/file.h
@@ -88,6 +88,9 @@ foffset_get(struct file *fp)
 	return (foffset_lock(fp, FOF_NOLOCK));
 }
 
+/* XXX pollution? */
+struct sendfile_sync;
+
 typedef int fo_rdwr_t(struct file *fp, struct uio *uio,
 		    struct ucred *active_cred, int flags,
 		    struct thread *td);
@@ -107,7 +110,8 @@ typedef	int fo_chown_t(struct file *fp, uid_t uid, gid_t gid,
 		    struct ucred *active_cred, struct thread *td);
 typedef int fo_sendfile_t(struct file *fp, int sockfd, struct uio *hdr_uio,
 		    struct uio *trl_uio, off_t offset, size_t nbytes,
-		    off_t *sent, int flags, int kflags, struct thread *td);
+		    off_t *sent, int flags, int kflags,
+		    struct sendfile_sync *sfs, struct thread *td);
 typedef int fo_seek_t(struct file *fp, off_t offset, int whence,
 		    struct thread *td);
 typedef	int fo_flags_t;
@@ -368,11 +372,11 @@ fo_chown(struct file *fp, uid_t uid, gid_t gid, struct ucred *active_cred,
 static __inline int
 fo_sendfile(struct file *fp, int sockfd, struct uio *hdr_uio,
     struct uio *trl_uio, off_t offset, size_t nbytes, off_t *sent, int flags,
-    int kflags, struct thread *td)
+    int kflags, struct sendfile_sync *sfs, struct thread *td)
 {
 
 	return ((*fp->f_ops->fo_sendfile)(fp, sockfd, hdr_uio, trl_uio, offset,
-	    nbytes, sent, flags, kflags, td));
+	    nbytes, sent, flags, kflags, sfs, td));
 }
 
 static __inline int